High Output Alternator??
Pro
Joined: Dec 2013
Posts: 627
Likes: 181
From: west coast of Canada
Some old posts on alternators HTH 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
Last edited by dadaroo; 05-23-2016 at 07:27 AM.
Originally Posted by GCG
This is good info:
1) 97-01 Valeo Regulator 2542521B (M530) $32.99
2) 02-04 Valeo Regulator 2542499 (M520) $32.00
Safer than replacing the whole alternator and finding incompatibilities later on, and definitely cheaper!
Has anybody tried just to replace the worn out brushes in the old regulators?
FYI....We ordered the 2nd one listed because he has an '02. Come to find out, it was the wrong one. We needed the first one listed
I seldom perform preventive maintenance, but with 140K on the clock, and some long trips coming up, I did not want to risk a worn brush issue with the alternator while I was out of town.
I watched an excellent youtube video on replacing the brushes titled:
"Valeo alternator repair,common problem brush change"
The brushes are 4.5 x 6.5 x 15 mm and are available on the auction site: 10 brushes for $10 shipped to your house from China...and 6 weeks shipping time.
I have an early 02 and have the 110 Amp alternator which uses the M530 regulator assembly. I had one issue removing the regulator assembly, there were two obvious nuts, and two screws hidden under RTV. If you take a look at the pic of the M530 on the ebay site above, the two large mounting holes are visible, and at the top of the picture and to the right of the brushes, are two ring terminals. The screws securing the ring terminals are under the RTV. After removal, the regulator lifts right out.
I cleaned up the ring terminal with crocus cloth, soldered in the new brushes, and all was good. Total of one hour and $10. And a lifetime supply of brushes!
I had maybe 25% life left in the original brushes. Bearings seemed to be in excellent shape
Originally Posted by fmvette9
I seldom perform preventive maintenance, but with 140K on the clock, and some long trips coming up, I did not want to risk a worn brush issue with the alternator while I was out of town.
I watched an excellent youtube video on replacing the brushes titled:
"Valeo alternator repair,common problem brush change"
The brushes are 4.5 x 6.5 x 15 mm and are available on the auction site: 10 brushes for $10 shipped to your house from China...and 6 weeks shipping time.
I have an early 02 and have the 110 Amp alternator which uses the M530 regulator assembly. I had one issue removing the regulator assembly, there were two obvious nuts, and two screws hidden under RTV. If you take a look at the pic of the M530 on the ebay site above, the two large mounting holes are visible, and at the top of the picture and to the right of the brushes, are two ring terminals. The screws securing the ring terminals are under the RTV. After removal, the regulator lifts right out.
I cleaned up the ring terminal with crocus cloth, soldered in the new brushes, and all was good. Total of one hour and $10. And a lifetime supply of brushes!
I had maybe 25% life left in the original brushes. Bearings seemed to be in excellent shape.
Thanks to everyone with the replies! My friend actually took it to an alternator rebuild shop in Raleigh, NC, and they did great!! It ended up being bad bearings. It was actually cheaper than a replacement, and it works awesome. So glad I have this forum
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
Last edited by dadaroo; 05-23-2016 at 07:27 AM.
Originally Posted by GCG
This is good info:
1) 97-01 Valeo Regulator 2542521B (M530) $32.99
2) 02-04 Valeo Regulator 2542499 (M520) $32.00
Safer than replacing the whole alternator and finding incompatibilities later on, and definitely cheaper!
Has anybody tried just to replace the worn out brushes in the old regulators?
FYI....We ordered the 2nd one listed because he has an '02. Come to find out, it was the wrong one. We needed the first one listed
I seldom perform preventive maintenance, but with 140K on the clock, and some long trips coming up, I did not want to risk a worn brush issue with the alternator while I was out of town.
I watched an excellent youtube video on replacing the brushes titled:
"Valeo alternator repair,common problem brush change"
The brushes are 4.5 x 6.5 x 15 mm and are available on the auction site: 10 brushes for $10 shipped to your house from China...and 6 weeks shipping time.
I have an early 02 and have the 110 Amp alternator which uses the M530 regulator assembly. I had one issue removing the regulator assembly, there were two obvious nuts, and two screws hidden under RTV. If you take a look at the pic of the M530 on the ebay site above, the two large mounting holes are visible, and at the top of the picture and to the right of the brushes, are two ring terminals. The screws securing the ring terminals are under the RTV. After removal, the regulator lifts right out.
I cleaned up the ring terminal with crocus cloth, soldered in the new brushes, and all was good. Total of one hour and $10. And a lifetime supply of brushes!
I had maybe 25% life left in the original brushes. Bearings seemed to be in excellent shape
Originally Posted by fmvette9
I seldom perform preventive maintenance, but with 140K on the clock, and some long trips coming up, I did not want to risk a worn brush issue with the alternator while I was out of town.
I watched an excellent youtube video on replacing the brushes titled:
"Valeo alternator repair,common problem brush change"
The brushes are 4.5 x 6.5 x 15 mm and are available on the auction site: 10 brushes for $10 shipped to your house from China...and 6 weeks shipping time.
I have an early 02 and have the 110 Amp alternator which uses the M530 regulator assembly. I had one issue removing the regulator assembly, there were two obvious nuts, and two screws hidden under RTV. If you take a look at the pic of the M530 on the ebay site above, the two large mounting holes are visible, and at the top of the picture and to the right of the brushes, are two ring terminals. The screws securing the ring terminals are under the RTV. After removal, the regulator lifts right out.
I cleaned up the ring terminal with crocus cloth, soldered in the new brushes, and all was good. Total of one hour and $10. And a lifetime supply of brushes!
I had maybe 25% life left in the original brushes. Bearings seemed to be in excellent shape.
Thanks to everyone with the replies! My friend actually took it to an alternator rebuild shop in Raleigh, NC, and they did great!! It ended up being bad bearings. It was actually cheaper than a replacement, and it works awesome. So glad I have this forum
Drifting
Joined: Sep 2017
Posts: 1,962
Likes: 694
From: Avon Lake OH
Wow, lots of info above, thanks!! Just encase anyone needs to replace the voltage regulator in their older 110 Amp C5 #10246634 alternator, here is what I did;
https://www.corvetteforum.com/forums...post1605390230
https://www.maniacelectricmotors.com...yH46FTz61JXKQX
https://www.corvetteforum.com/forums...post1605390230
https://www.maniacelectricmotors.com...yH46FTz61JXKQX
Heel & Toe
Joined: Jul 2008
Posts: 21
Likes: 7
From: Bfe, ohio
Last edited by itsnick; Jun 18, 2025 at 11:03 PM.
Heel & Toe
Joined: Jul 2008
Posts: 21
Likes: 7
From: Bfe, ohio
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,595
Likes: 4,055
From: Cape Coral, Florida
Doing a voltage drop check you place one lead on battery positive and other lead on the B+ cable on the alternator and read the difference…on the negative side you check battery negative and the alternator case noting the difference again…the limit is .5 volts on either side but normally you see less than that…just think of a voltmeter as a “difference meter”…the alternator B+ cable and the battery positive cable are joined down at the starter solenoid so if there is a bad connection there the battery will not be charged…this test is usually done at 2500 RPM with loads on the electrical system…high beams, blower on high, rear defogger and AC on.
Heel & Toe
Joined: Jul 2008
Posts: 21
Likes: 7
From: Bfe, ohio
Doing a voltage drop check you place one lead on battery positive and other lead on the B+ cable on the alternator and read the difference…on the negative side you check battery negative and the alternator case noting the difference again…the limit is .5 volts on either side but normally you see less than that…just think of a voltmeter as a “difference meter”…the alternator B+ cable and the battery positive cable are joined down at the starter solenoid so if there is a bad connection there the battery will not be charged…this test is usually done at 2500 RPM with loads on the electrical system…high beams, blower on high, rear defogger and AC on.
https://youtu.be/fYjuP8FBUu8?si=BdiNBxvZ-sNgQQZ4
https://youtu.be/fYjuP8FBUu8?si=BdiNBxvZ-sNgQQZ4
Once I got out of the city and was driving 55-60 mph on back roads it worked it's way back up to 13.7 - 13.9 after about 8-10 mins
So I guess It's just borderline putting enough out when it's heat soaked in town.
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Team Owner
Joined: Oct 1999
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From: Guinness Its whats for B'fast JAWGA
CI 3-4-5-9 Veteran
Some good info in here. Ericdwong rebuit his alternator and Id like to add the links as some of this stuff can be hard to find when searching.
https://www.corvetteforum.com/forums...-bearings.html
https://www.corvetteforum.com/forums...intenance.html
https://www.corvetteforum.com/forums...-bearings.html
https://www.corvetteforum.com/forums...intenance.html
Heel & Toe
Joined: Jul 2008
Posts: 21
Likes: 7
From: Bfe, ohio
Some good info in here. Ericdwong rebuit his alternator and Id like to add the links as some of this stuff can be hard to find when searching.
https://www.corvetteforum.com/forums...-bearings.html
https://www.corvetteforum.com/forums...intenance.html
https://www.corvetteforum.com/forums...-bearings.html
https://www.corvetteforum.com/forums...intenance.html
Last edited by itsnick; Jun 27, 2025 at 11:15 PM.