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I put this together to try and provide factual information. If anyone finds an issue I will be glad to correct.
How alternators work.
The alternator has a Rotor in the center with wire windings that spins on two bearings. Surrounding that is the stationary Stator with its own windings that you can see through the air cooling openings. If adequate DC voltage and current is applied to the Rotor while it spins it creates a rotating magnetic field and that induces an AC voltage and current in the Stator. This is called “flashing” the field in the Stator. The alternator has a regulator that converts this AC output into DC for charging.
Here is how the alternator works in the C5. Also refer to the schematic below.
Big picture, the large Red wire on the far left in the schematic below is the DC voltage output from the alternator to charge the battery, via the starter. The smaller Red wire (terminal D) to the right of it is used to monitor that voltage there and provide “feedback” to the alternator regulator in order for it to provide (regulate) the correct charging voltage.
The 2 wires (Gray and Red) on the right are interfaces with the PCM (Powertrain Control Module).
The Red wire (terminal B) from the PCM is called the “Turn On” signal and is also called the L terminal. The PCM provides this when you turn the ignition to ON. It is just DC voltage and current that is fed to the alternator Rotor which is the part that spins. As it spins it creates a rotating magnetic field that produces an AC voltage and current in the Stator which is stationary. The regulator senses that the Stator is producing voltage and now takes over control. It also converts the AC to DC. Some of this DC is now used to power the Rotor while most of it is used to provide the charging voltage. The regulator also can turn OFF and ON the alternator output to regulate the charging voltage. It does this by turning OFF and ON the power it provides to the Rotor. This aspect is discussed next.
The Gray wire (terminal C) just sends a signal to the PCM as to how the alternator is performing. It is also referred to as the F terminal. This is called a Duty Cycle signal which is a Pulse Width Modulated (PWM) signal. The Regulator controls the output voltage by turning the alternator OFF and ON to control the voltage. This Duty Cycle signal can be from 0 to 100% with 100% being the regulator has the alternator fully “ON” providing voltage and 50% would mean it is “OFF” half the time.. The PCM only monitors this and will throw a DIC Charging Fault message and code P1638 (99-04) if it detects performance outside of preset parameters. I can’t find where 97 and 98s show this code in their FSM (Factory Service Manual).
The only thing controlling the current output of the alternator are the loads throughout the car. Based on the loads the alternator will provide as much current as it was designed to do. The regulator just works to try and maintain the correct charging voltage over the range of current loads it experiences. Ohm’s law is at work. Voltage=Current X Resistance.
One thing of interest is that when at idle if the PCM detects a high Duty Cycle (alternator working hard to maintain charging voltage) then the PCM will command an increase in idle speed. This is discussed in the FSM.
Some common issues people have when replacing C5 alternators.
1. Many GM regulators look like the C5 ones but are not correct.
People get a replacement that does not have the feedback design to the PCM for monitoring the Duty Cycle. This causes a PCM Charging System Fault DIC message but the alternator can still charge the battery.
2. People get an alternator but it does not immediately create “Turn On” voltage or current for the Rotor to activate/flash voltage and current in the Stator. In some cases one has to rev the engine to 1500-2000 rpms before the alternator starts charging on its own.
3. People turn in their core before they get a functioning replacement. That prevents their ability to have theirs rebuilt. This happens quite often as seen here on this Forum.
NOTES:
1. From 97-00 all Automatics had a solid alternator pulley.
2. From 97-04 all Manual cars had a solid alternator pulley.
3. From 01 to 04 the Automatic cars had a Decoupler pulley to help "synchronize" the belt drive system for improved engine efficiency, reduced Noise/Vibration/Harshness (NVH) and increased component life. It helps eliminate the influence of the alternator on the serpentine belt drive. It is kind of like a suspension for your alternator. I have heard GM used them on the automatics to improve idling characteristics.
The alternator decoupler pulley will have a spring and a clutch inside. The internal spring absorbs vibration from the engine belt. The clutch inside the pulley allows the alternator rotor to coast to a stop after the engine has been shut off. The clutch also allows the alternator to spin faster than the engine during hard shifting thus eliminating annoying belt chirping. I can’t say why the manuals didn’t get the design.
Decouplers can to used/added to manuals
4. From 97-02 all C5s were 110 amp. In 03-04 they were 145 amp. Some of the 2002 cars might have been 145 but I can’t confirm.
5. Valeo, a French company, was the supplier to GM for the C5. I think some were made by them in Mexico.
6. 145 amp ones can be used in all years and will charge. HOWEVER, in the 97-00 years they will probably throw a Charge Fault. From 01-04 the PCM Duty Cycle monitoring is the same and not like the earlier years. I plan to use one of my NOS 145 amp Valeo ones to test that theory in my 01 in the near future.
See the following FSM info on PCM Duty Cycle monitoring.
Part Number Information:
I have tried to identify the original GM part numbers for each year alternators. If you find an error please let me know.
From 97-2000 they used a 110amp one with P/N 10246634
From 2001-2002 on Manual cars they used the 110amp 10246634 also.
From 2001-2002 on Automatics they used a 110 amp 10316182 since they used a decoupler. It should have been identical to 10246634 except it had a decoupler.
For 2003-2004 they used a 145 amp alternator. 10305776 for manuals and 10353440 for Autos with decoupler.
Some information says some 2002s came with 145 amp units.
110 amp units use a Valeo Regulator M530
145 amp units use a Valeo Regulator M520
PCM Duty Cycle Monitoring: This was done to try and address Note 5 above.
I know a knowledgeable person who tried to put a new Valeo 145 amp unit in his 99 and it threw a Charge Fault.
I had a chance to go thru every year C5 in my GM database to provide the following information. I make no conclusions from what I found. I am still trying to absorb what I found and did not find.
As far as I could find there are only two things that can create the Charge Fault message which are:
Low voltage or high voltage as detected by the PCM
P1638 related to the Duty Cycle monitored by the PCM
97 and 98:
I could not find any information that P1638 is even a code there. Not listed in the DTCs or diagnostics. I even have access to Prodemand.com database (like Alldata) and found nothing.
99 and 00:
P1638
Circuit Description
The generator has an input to the PCM called the F Terminal to indicate the percentage of total capacity that the generator is producing. This signal is detected by the PCM as a duty cycle from the generator and displayed on the scan tool as a percentage. The PCM can monitor the generators output under all conditions to determine if it is functioning normally.
When there is low demand from the electrical system on the generator, a low duty cycle
percentage will be displayed. As more accessory load is placed on the generator, the duty cycle output detected by the PCM will approach 100%. A normally functioning generating system will never reach 100% as indicated on the scan tool.
Conditions for Running the DTC
The ignition switch in the ON position or the engine is operating.
Conditions for Setting the DTC
• The F Terminal indicates a duty cycle not between 10 and 40% with the ignition ON and the
engine OFF or the duty cycle is less than 5% with the engine running.
• All conditions met for 6 seconds.
01 thru 04:
P1638
Circuit Description
The PCM uses the generator field duty cycle signal circuit to monitor the duty cycle of the
generator. The generator field duty cycle signal circuit connects to the high side of the field winding in the generator. A pulse width modulated (PWM) high side driver in the voltage regulator turns the field winding ON and OFF. The PCM uses the PWM signal input to determine the generator load on the engine. This allows the PCM to adjust the idle speed to compensate for high electrical loads.
The PCM monitors the state of the generator field duty cycle signal circuit. When the key is in the RUN position and the engine is OFF, the PCM should detect a duty cycle near 0 percent. However, when the engine is running, the duty cycle should be between 5 percent and 100 percent. The PCM monitors the PWM signal using a key ON test and a RUN test. During the tests, if the PCM detects an out of range PWM signal, DTC P1638 will set. When the DTC sets, the PCM will send a class 2 serial data message to the IPC to illuminate the Charge System Fault message
Conditions for Running the DTC
Key ON Test
No generator, CKP sensors, or CMP sensor DTCs are set.
• The key is in the RUN position.
• The engine is not running.
Run Test
• No generator, CKP sensors, or CMP sensor DTCs are set.
• The engine is less than 3000 RPM.
Conditions for Setting the DTC
• During the key ON test, the PCM detects a PWM signal greater than 65 percent for at least
5 seconds.
OR
• During the RUN test, the PCM detects a PWM signal less than 5 percent for at least
15 seconds.
Related DTCs:
P0562, P0563, and P1637 can be related to the alternator and charging circuit but I have not included them as I was focusing on Charge System Fault DIC message issues.
"One thing of interest is that when at idle if the PCM detects a high Duty Cycle (alternator working hard to maintain charging voltage) then the PCM will command an increase in idle speed. This is discussed in the FSM."
I recently noticed when coasting up to a light (6sp) with the AC blazing away - the idle stays higher for a moment or two and then settles back down again. I wonder if this "idle increase mechanism" is at work?
"One thing of interest is that when at idle if the PCM detects a high Duty Cycle (alternator working hard to maintain charging voltage) then the PCM will command an increase in idle speed. This is discussed in the FSM."
I recently noticed when coasting up to a light (6sp) with the AC blazing away - the idle stays higher for a moment or two and then settles back down again. I wonder if this "idle increase mechanism" is at work?
I have a rattling noise coming from the engine, and it sounds like it's coming from the alternator. After removing the serpentine belt, I noticed that the bearings feel smooth, but the pulley rocks a little relative to the shaft. Is this normal/ok? could this relative motion really be causing the rattling sound? Am I wasting $200 to replace the alternator?
Thanks for your time, and knowledge. I really don't want to give the Chevy dealer $300-400 just to tell me what the noise is.
Originally Posted by dadaroo
I put this together to try and provide factual information. If anyone finds an issue I will be glad to correct.
How alternators work.
The alternator has a Rotor in the center with wire windings that spins on two bearings. Surrounding that is the stationary Stator with its own windings that you can see through the air cooling openings. If adequate DC voltage and current is applied to the Rotor while it spins it creates a rotating magnetic field and that induces an AC voltage and current in the Stator. This is called “flashing” the field in the Stator. The alternator has a regulator that converts this AC output into DC for charging.
Here is how the alternator works in the C5. Also refer to the schematic below.
Big picture, the large Red wire on the far left in the schematic below is the DC voltage output from the alternator to charge the battery, via the starter. The smaller Red wire (terminal D) to the right of it is used to monitor that voltage there and provide “feedback” to the alternator regulator in order for it to provide (regulate) the correct charging voltage.
The 2 wires (Gray and Red) on the right are interfaces with the PCM (Powertrain Control Module).
The Red wire (terminal B) from the PCM is called the “Turn On” signal and is also called the L terminal. The PCM provides this when you turn the ignition to ON. It is just DC voltage and current that is fed to the alternator Rotor which is the part that spins. As it spins it creates a rotating magnetic field that produces an AC voltage and current in the Stator which is stationary. The regulator senses that the Stator is producing voltage and now takes over control. It also converts the AC to DC. Some of this DC is now used to power the Rotor while most of it is used to provide the charging voltage. The regulator also can turn OFF and ON the alternator output to regulate the charging voltage. It does this by turning OFF and ON the power it provides to the Rotor. This aspect is discussed next.
The Gray wire (terminal C) just sends a signal to the PCM as to how the alternator is performing. It is also referred to as the F terminal. This is called a Duty Cycle signal which is a Pulse Width Modulated (PWM) signal. The Regulator controls the output voltage by turning the alternator OFF and ON to control the voltage. This Duty Cycle signal can be from 0 to 100% with 100% being the regulator has the alternator fully “ON” providing voltage and 50% would mean it is “OFF” half the time.. The PCM only monitors this and will throw a DIC Charging Fault message and code P1638 (99-04) if it detects performance outside of preset parameters. I can’t find where 97 and 98s show this code in their FSM (Factory Service Manual).
The only thing controlling the current output of the alternator are the loads throughout the car. Based on the loads the alternator will provide as much current as it was designed to do. The regulator just works to try and maintain the correct charging voltage over the range of current loads it experiences. Ohm’s law is at work. Voltage=Current X Resistance.
One thing of interest is that when at idle if the PCM detects a high Duty Cycle (alternator working hard to maintain charging voltage) then the PCM will command an increase in idle speed. This is discussed in the FSM.
Some common issues people have when replacing C5 alternators.
1. Many GM regulators look like the C5 ones but are not correct.
People get a replacement that does not have the feedback design to the PCM for monitoring the Duty Cycle. This causes a PCM Charging System Fault DIC message but the alternator can still charge the battery.
2. People get an alternator but it does not immediately create “Turn On” voltage or current for the Rotor to activate/flash voltage and current in the Stator. In some cases one has to rev the engine to 1500-2000 rpms before the alternator starts charging on its own.
3. People turn in their core before they get a functioning replacement. That prevents their ability to have theirs rebuilt. This happens quite often as seen here on this Forum.
NOTES:
1. From 97-00 all Automatics had a solid alternator pulley.
2. From 97-04 all Manual cars had a solid alternator pulley.
3. From 01 to 04 the Automatic cars had a Decoupler pulley to help "synchronize" the belt drive system for improved engine efficiency, reduced Noise/Vibration/Harshness (NVH) and increased component life. It helps eliminate the influence of the alternator on the serpentine belt drive. It is kind of like a suspension for your alternator. I have heard GM used them on the automatics to improve idling characteristics.
The alternator decoupler pulley will have a spring and a clutch inside. The internal spring absorbs vibration from the engine belt. The clutch inside the pulley allows the alternator rotor to coast to a stop after the engine has been shut off. The clutch also allows the alternator to spin faster than the engine during hard shifting thus eliminating annoying belt chirping. I can’t say why the manuals didn’t get the design.
Decouplers can to used/added to manuals
4. From 97-02 all C5s were 110 amp. In 03-04 they were 145 amp. Some of the 2002 cars might have been 145 but I can’t confirm.
5. Valeo, a French company, was the supplier to GM for the C5. I think some were made by them in Mexico.
6. 145 amp ones can be used in all years and will charge. HOWEVER, in the 97-00 years they will probably throw a Charge Fault. From 01-04 the PCM Duty Cycle monitoring is the same and not like the earlier years. I plan to use one of my NOS 145 amp Valeo ones to test that theory in my 01 in the near future.
See the following FSM info on PCM Duty Cycle monitoring.
Part Number Information:
I have tried to identify the original GM part numbers for each year alternators. If you find an error please let me know.
From 97-2000 they used a 110amp one with P/N 10246634
From 2001-2002 on Manual cars they used the 110amp 10246634 also.
From 2001-2002 on Automatics they used a 110 amp 10316182 since they used a decoupler. It should have been identical to 10246634 except it had a decoupler.
For 2003-2004 they used a 145 amp alternator. 10305776 for manuals and 10353440 for Autos with decoupler.
Some information says some 2002s came with 145 amp units.
110 amp units use a Valeo Regulator M530
145 amp units use a Valeo Regulator M520
PCM Duty Cycle Monitoring: This was done to try and address Note 5 above.
I know a knowledgeable person who tried to put a new Valeo 145 amp unit in his 99 and it threw a Charge Fault.
I had a chance to go thru every year C5 in my GM database to provide the following information. I make no conclusions from what I found. I am still trying to absorb what I found and did not find.
As far as I could find there are only two things that can create the Charge Fault message which are:
Low voltage or high voltage as detected by the PCM
P1638 related to the Duty Cycle monitored by the PCM
97 and 98:
I could not find any information that P1638 is even a code there. Not listed in the DTCs or diagnostics. I even have access to Prodemand.com database (like Alldata) and found nothing.
99 and 00:
P1638
Circuit Description
The generator has an input to the PCM called the F Terminal to indicate the percentage of total capacity that the generator is producing. This signal is detected by the PCM as a duty cycle from the generator and displayed on the scan tool as a percentage. The PCM can monitor the generators output under all conditions to determine if it is functioning normally.
When there is low demand from the electrical system on the generator, a low duty cycle
percentage will be displayed. As more accessory load is placed on the generator, the duty cycle output detected by the PCM will approach 100%. A normally functioning generating system will never reach 100% as indicated on the scan tool.
Conditions for Running the DTC
The ignition switch in the ON position or the engine is operating.
Conditions for Setting the DTC
• The F Terminal indicates a duty cycle not between 10 and 40% with the ignition ON and the
engine OFF or the duty cycle is less than 5% with the engine running.
• All conditions met for 6 seconds.
01 thru 04:
P1638
Circuit Description
The PCM uses the generator field duty cycle signal circuit to monitor the duty cycle of the
generator. The generator field duty cycle signal circuit connects to the high side of the field winding in the generator. A pulse width modulated (PWM) high side driver in the voltage regulator turns the field winding ON and OFF. The PCM uses the PWM signal input to determine the generator load on the engine. This allows the PCM to adjust the idle speed to compensate for high electrical loads.
The PCM monitors the state of the generator field duty cycle signal circuit. When the key is in the RUN position and the engine is OFF, the PCM should detect a duty cycle near 0 percent. However, when the engine is running, the duty cycle should be between 5 percent and 100 percent. The PCM monitors the PWM signal using a key ON test and a RUN test. During the tests, if the PCM detects an out of range PWM signal, DTC P1638 will set. When the DTC sets, the PCM will send a class 2 serial data message to the IPC to illuminate the Charge System Fault message
Conditions for Running the DTC
Key ON Test
No generator, CKP sensors, or CMP sensor DTCs are set.
• The key is in the RUN position.
• The engine is not running.
Run Test
• No generator, CKP sensors, or CMP sensor DTCs are set.
• The engine is less than 3000 RPM.
Conditions for Setting the DTC
• During the key ON test, the PCM detects a PWM signal greater than 65 percent for at least
5 seconds.
OR
• During the RUN test, the PCM detects a PWM signal less than 5 percent for at least
15 seconds.
Related DTCs:
P0562, P0563, and P1637 can be related to the alternator and charging circuit but I have not included them as I was focusing on Charge System Fault DIC message issues.
I put this together to try and provide factual information. If anyone finds an issue I will be glad to correct.
How alternators work.
The alternator has a Rotor in the center with wire windings that spins on two bearings. Surrounding that is the stationary Stator with its own windings that you can see through the air cooling openings. If adequate DC voltage and current is applied to the Rotor while it spins it creates a rotating magnetic field and that induces an AC voltage and current in the Stator. This is called “flashing” the field in the Stator. The alternator has a regulator that converts this AC output into DC for charging.
Here is how the alternator works in the C5. Also refer to the schematic below.
Big picture, the large Red wire on the far left in the schematic below is the DC voltage output from the alternator to charge the battery, via the starter. The smaller Red wire (terminal D) to the right of it is used to monitor that voltage there and provide “feedback” to the alternator regulator in order for it to provide (regulate) the correct charging voltage.
The 2 wires (Gray and Red) on the right are interfaces with the PCM (Powertrain Control Module).
The Red wire (terminal B) from the PCM is called the “Turn On” signal and is also called the L terminal. The PCM provides this when you turn the ignition to ON. It is just DC voltage and current that is fed to the alternator Rotor which is the part that spins. As it spins it creates a rotating magnetic field that produces an AC voltage and current in the Stator which is stationary. The regulator senses that the Stator is producing voltage and now takes over control. It also converts the AC to DC. Some of this DC is now used to power the Rotor while most of it is used to provide the charging voltage. The regulator also can turn OFF and ON the alternator output to regulate the charging voltage. It does this by turning OFF and ON the power it provides to the Rotor. This aspect is discussed next.
The Gray wire (terminal C) just sends a signal to the PCM as to how the alternator is performing. It is also referred to as the F terminal. This is called a Duty Cycle signal which is a Pulse Width Modulated (PWM) signal. The Regulator controls the output voltage by turning the alternator OFF and ON to control the voltage. This Duty Cycle signal can be from 0 to 100% with 100% being the regulator has the alternator fully “ON” providing voltage and 50% would mean it is “OFF” half the time.. The PCM only monitors this and will throw a DIC Charging Fault message and code P1638 (99-04) if it detects performance outside of preset parameters. I can’t find where 97 and 98s show this code in their FSM (Factory Service Manual).
The only thing controlling the current output of the alternator are the loads throughout the car. Based on the loads the alternator will provide as much current as it was designed to do. The regulator just works to try and maintain the correct charging voltage over the range of current loads it experiences. Ohm’s law is at work. Voltage=Current X Resistance.
One thing of interest is that when at idle if the PCM detects a high Duty Cycle (alternator working hard to maintain charging voltage) then the PCM will command an increase in idle speed. This is discussed in the FSM.
Some common issues people have when replacing C5 alternators.
1. Many GM regulators look like the C5 ones but are not correct.
People get a replacement that does not have the feedback design to the PCM for monitoring the Duty Cycle. This causes a PCM Charging System Fault DIC message but the alternator can still charge the battery.
2. People get an alternator but it does not immediately create “Turn On” voltage or current for the Rotor to activate/flash voltage and current in the Stator. In some cases one has to rev the engine to 1500-2000 rpms before the alternator starts charging on its own.
3. People turn in their core before they get a functioning replacement. That prevents their ability to have theirs rebuilt. This happens quite often as seen here on this Forum.
NOTES:
1. From 97-00 all Automatics had a solid alternator pulley.
2. From 97-04 all Manual cars had a solid alternator pulley.
3. From 01 to 04 the Automatic cars had a Decoupler pulley to help "synchronize" the belt drive system for improved engine efficiency, reduced Noise/Vibration/Harshness (NVH) and increased component life. It helps eliminate the influence of the alternator on the serpentine belt drive. It is kind of like a suspension for your alternator. I have heard GM used them on the automatics to improve idling characteristics.
The alternator decoupler pulley will have a spring and a clutch inside. The internal spring absorbs vibration from the engine belt. The clutch inside the pulley allows the alternator rotor to coast to a stop after the engine has been shut off. The clutch also allows the alternator to spin faster than the engine during hard shifting thus eliminating annoying belt chirping. I can’t say why the manuals didn’t get the design.
Decouplers can to used/added to manuals
4. From 97-02 all C5s were 110 amp. In 03-04 they were 145 amp. Some of the 2002 cars might have been 145 but I can’t confirm.
5. Valeo, a French company, was the supplier to GM for the C5. I think some were made by them in Mexico.
6. 145 amp ones can be used in all years and will charge. HOWEVER, in the 97-00 years they will probably throw a Charge Fault. From 01-04 the PCM Duty Cycle monitoring is the same and not like the earlier years. I plan to use one of my NOS 145 amp Valeo ones to test that theory in my 01 in the near future.
See the following FSM info on PCM Duty Cycle monitoring.
Part Number Information:
I have tried to identify the original GM part numbers for each year alternators. If you find an error please let me know.
From 97-2000 they used a 110amp one with P/N 10246634
From 2001-2002 on Manual cars they used the 110amp 10246634 also.
From 2001-2002 on Automatics they used a 110 amp 10316182 since they used a decoupler. It should have been identical to 10246634 except it had a decoupler.
For 2003-2004 they used a 145 amp alternator. 10305776 for manuals and 10353440 for Autos with decoupler.
Some information says some 2002s came with 145 amp units.
110 amp units use a Valeo Regulator M530
145 amp units use a Valeo Regulator M520
PCM Duty Cycle Monitoring: This was done to try and address Note 5 above.
I know a knowledgeable person who tried to put a new Valeo 145 amp unit in his 99 and it threw a Charge Fault.
I had a chance to go thru every year C5 in my GM database to provide the following information. I make no conclusions from what I found. I am still trying to absorb what I found and did not find.
As far as I could find there are only two things that can create the Charge Fault message which are:
Low voltage or high voltage as detected by the PCM
P1638 related to the Duty Cycle monitored by the PCM
97 and 98:
I could not find any information that P1638 is even a code there. Not listed in the DTCs or diagnostics. I even have access to Prodemand.com database (like Alldata) and found nothing.
99 and 00:
P1638
Circuit Description
The generator has an input to the PCM called the F Terminal to indicate the percentage of total capacity that the generator is producing. This signal is detected by the PCM as a duty cycle from the generator and displayed on the scan tool as a percentage. The PCM can monitor the generators output under all conditions to determine if it is functioning normally.
When there is low demand from the electrical system on the generator, a low duty cycle
percentage will be displayed. As more accessory load is placed on the generator, the duty cycle output detected by the PCM will approach 100%. A normally functioning generating system will never reach 100% as indicated on the scan tool.
Conditions for Running the DTC
The ignition switch in the ON position or the engine is operating.
Conditions for Setting the DTC
• The F Terminal indicates a duty cycle not between 10 and 40% with the ignition ON and the
engine OFF or the duty cycle is less than 5% with the engine running.
• All conditions met for 6 seconds.
01 thru 04:
P1638
Circuit Description
The PCM uses the generator field duty cycle signal circuit to monitor the duty cycle of the
generator. The generator field duty cycle signal circuit connects to the high side of the field winding in the generator. A pulse width modulated (PWM) high side driver in the voltage regulator turns the field winding ON and OFF. The PCM uses the PWM signal input to determine the generator load on the engine. This allows the PCM to adjust the idle speed to compensate for high electrical loads.
The PCM monitors the state of the generator field duty cycle signal circuit. When the key is in the RUN position and the engine is OFF, the PCM should detect a duty cycle near 0 percent. However, when the engine is running, the duty cycle should be between 5 percent and 100 percent. The PCM monitors the PWM signal using a key ON test and a RUN test. During the tests, if the PCM detects an out of range PWM signal, DTC P1638 will set. When the DTC sets, the PCM will send a class 2 serial data message to the IPC to illuminate the Charge System Fault message
Conditions for Running the DTC
Key ON Test
No generator, CKP sensors, or CMP sensor DTCs are set.
• The key is in the RUN position.
• The engine is not running.
Run Test
• No generator, CKP sensors, or CMP sensor DTCs are set.
• The engine is less than 3000 RPM.
Conditions for Setting the DTC
• During the key ON test, the PCM detects a PWM signal greater than 65 percent for at least
5 seconds.
OR
• During the RUN test, the PCM detects a PWM signal less than 5 percent for at least
15 seconds.
Related DTCs:
P0562, P0563, and P1637 can be related to the alternator and charging circuit but I have not included them as I was focusing on Charge System Fault DIC message issues.
Mr. Sam
Thanks for your time explaining the alternator in the C5. I have changed hundreds of alternators in my years as a mechanic but didn't know exactly why my 03 had a clutch on it. In fact I purchased my new to me C5 with a new rebuilt Ac Delco alternator installed. After only 400 miles it cooked itself! I checked everything in the charging system and the alternator was definitely fried. Of course it wasn't covered by the warranty because of the changes in ownership. I purchased a new not rebuilt one from Amazon with a two year warranty! And I got it from there open box warehouse deals for less than $70.00!!! If fit perfectly and is putting out 13.7-14 volts at idle. I was lucky finding one that I wanted that was all new construction with a good warranty and a smoken deal on top of it. If anyone is interested in the brand it's Premier Gear. I'm usually a AC Delco man but I didn't want to pay almost $400 for one from them. Also there warranty wasn't as good as Premier Gear. I don't think you'll be able to get the same deal as I got but the usual price is less than $180 which is still a bargain compared to most. Thanks again for your interesting indepth info it was very interesting and I learned a few things. I guess you can teach a old dog new tricks!
Last edited by My1stONE; Jul 8, 2018 at 11:37 AM.
Reason: Miss spelled word
Friday, is my drive Vette day, I headed to work in my blue flamed 03 supercharged corvette, when I cranked it up I got a reading that said, Charge System Fault, so I reset and headed off to work, with in a few minutes I looked at by battery voltage and it was around 10, so I returned home got my truck and went to work, on the way home from my internet searching I decided to pick up a new alternator, upon the switch I noticed the CSF display was still on so I took the alternator off, got my return and had my alternator checked to which it read a 14.3. Tinkered with it all Friday evening with no success, got up Saturday morning tried a voltage drop test with no success looked at some utube videos, I blocked the car up to start unplugging connections and blowing them with canned air and after each connection clean I was going to check the voltage meter on the dash to see as I go if I had fixing the issue, here we go. THE VERY FIRST CONNECTION BEHIND THE DUAL FAN I CLEANED AND WENT TO THE BATTERY VOLTS IN THE GAUGES AND IMMEDIATELY IT WAS AT 11.4 AND QUICKLY TO 14.2.
I posteed this thinking it might just help someone save a lot of money, I am not much on mechanic shops.
CaoticVettes
Last edited by CaoticVettes4me; Oct 20, 2018 at 06:12 PM.
Thank you for this information. I have also read the thread about the battery going dead after three days as I am having this problem.
Using the troubleshooting instructions in that thread I have found that I have a 5 amp draw on the Red wire (B) when connecting my meter in series with the post. suggesting a bad diode in the rectifier supplying power to the stator when parked.
How would you suggest I proceed. I now see that I cannot just go out and put any alternator on
Friday, is my drive Vette day, I headed to work in my blue flamed 03 supercharged corvette, when I cranked it up I got a reading that said, Charge System Fault, so I reset and headed off to work, with in a few minutes I looked at by battery voltage and it was around 10, so I returned home got my truck and went to work, on the way home from my internet searching I decided to pick up a new alternator, upon the switch I noticed the CSF display was still on so I took the alternator off, got my return and had my alternator checked to which it read a 14.3. Tinkered with it all Friday evening with no success, got up Saturday morning tried a voltage drop test with no success looked at some utube videos, I blocked the car up to start unplugging connections and blowing them with canned air and after each connection clean I was going to check the voltage meter on the dash to see as I go if I had fixing the issue, here we go. THE VERY FIRST CONNECTION BEHIND THE DUAL FAN I CLEANED AND WENT TO THE BATTERY VOLTS IN THE GAUGES AND IMMEDIATELY IT WAS AT 11.4 AND QUICKLY TO 14.2.
I posteed this thinking it might just help someone save a lot of money, I am not much on mechanic shops.
CaoticVettes
No Sir, IT WAS MY POSITIVE CONNECTION TO MY SOLENOID, the stud was broken, replaced it & no issues with voltage at all!
Last edited by CaoticVettes4me; Apr 23, 2019 at 09:09 PM.
I just thought it might be useful to add here some additional information and links I have compiled over the years, in an effort to have a centralized point of exchange on this subject, instead of scattered bits and pieces.
What makes this alternator so peculiar is that it is excited when its voltage regulator receives a turn on signal of 10v at limited current provided by the PCM through the L wire. Not all regulators accept the turn on signal provided by the C5 PCM.
Another distinctive attribute described by Lionelhutz in this post:
The stock alternator has a soft turn-on regulator. You can watch how slowly the voltage increases when the engine starts. So, I suspect the message is caused by some aftermarket units that do not have a soft-start and basically jump to a high duty cycle until the voltage rises and the duty cycle drops again. The PCM is seeing the duty cycle go too high which triggers the charge fault message in the DIC.
In general, if the alternator is fine, people should be careful with unnecessary replacements. This could open Pandora's Box: plenty of horror stories documented in the forum!... In any case, DON'T turn-in the old alternator as core.
If there is a concern with the car's mileage and the normal wear on the alternator, check the links at the bottom of this post for rebuilding information. Perhaps all that's needed are new brushes.
For a potential rebuilt route, take a look at this post. It has info on the right regulators for both, 97-01 and 02-04. The price is around $30. Just to clarify, in case someone is wondering: new regulators include new brushes.
Alternator Design and Issues
