Guys....I have this same issue and it is driving me nuts! I saw the volts on the DIC ranging back and forth...then one NIGHT, crossing the Nevada desert I watched the volts drop 13...12.7....12.3......12.1.....12....11 .8......11.5......11.2....11.....10.9... .10.8......and one by one the computer shut down the unneccessary electronics.....then when my fuel pressure went from 60 to 50 and then 40 the car shut down. I replaced the alternator thinking that the issue. BTW..has a new Yellow Top Optima. The GM dealer bought replacement ($425.00 by the way) worked for about a month then did same thing on same desert trip (what is going on in the Nevada desert at night???). I finally took both alternators to Pep Boys and they ran a check showing both functioning normally. Put one back in car. Battery at FULL charge. Turned on car and got same "CHARGE SYSTEM FAULT" and no useful codes other than telling me voltage low...duh. Checked battery with my tester and showed full charge. Checked ALTERNATOR with car running and NO OUTPUT measured. NOW..GO FIGURE. I am stumped. And my car is grounded. Now I am driving my 96 Discovery and it is hurtin' me bad..
I have a 2001 Vert with an A and A Vortech supercharger. I ask this....could belt slippage completely stop any voltage from alternator? As I recall, the voltage reg is integral to the C5 alternator? SOMEBODY help me because I don't buy the slipping belt, bad battery (used two new Yellow Tops). Worse is the computer has decided NOT to be helpful either. Damn gremlins!!!!!

Ron

 

Are you using this procedure to look at codes?

https://www.corvetteforum.com/techti...D=26&TopicID=1

How long does it take once you see the voltage start to dip to completely shut the car down?

 

You need to check the codes. You may have a PCM problem not a battery or alternator problem. Here is a description of how the system works.

Charging System Description and Operation
Generator
The Valeo generator is electrically similar to earlier models. The generator features the following major components:

The delta stator
The rectifier bridge
The rotor with slip rings and brushes
A conventional pulley
The regulator
The pulley and the fan cool the slip ring and the frame.

The generator features permanently lubricated bearings. Service should only include tightening of mount components. Otherwise, replace the generator as a complete unit.

Regulator
The voltage regulator controls the rotor field current in order to limit the system voltage. When the field current is on, the regulator switches the current on and off at a rate of 400 cycles per second in order to perform the following functions:

Radio noise control
Obtain the correct average current needed for proper system voltage control
At high speeds, the on-time may be 10 percent with the off-time at 90 percent. At low speeds, the on-time may be 90 percent and the off-time 10 percent.

Circuit Description
The generator provides voltage to operate the vehicle's electrical system and to charge its battery. A magnetic field is created when current flows through the rotor. This field rotates as the rotor is driven by the engine, creating an AC voltage in the stator windings. The AC voltage is converted to DC by the rectifier bridge and is supplied to the electrical system at the battery terminal.

When the engine is running, the generator turn-on signal is sent to the generator from the PCM, turning on the regulator. The generator's voltage regulator controls current to the rotor, thereby controlling the output voltage. The rotor current is proportional to the electrical pulse width supplied by the regulator. When the engine is started, the regulator senses generator rotation by detecting AC voltage at the stator through an internal wire. Once the engine is running, the regulator varies the field current by controlling the pulse width. This regulates the generator output voltage for proper battery charging and electrical system operation. The generator F terminal is connected internally to the voltage regulator and externally to the PCM. When the voltage regulator detects a charging system problem, it grounds this circuit to signal the PCM that a problem exists. The PCM monitors the generator field duty cycle signal circuit. The system voltage sense circuit receives B+ voltage that is Hot At All Times through a fuse link that is connedted to the starter.. This voltage is used by the regulator as the reference for system voltage control.

Charging System Indicator(s)
CHARGE SYSTEM FAULT
The IPC illuminates the CHARGE SYSTEM FAULT indicator in the message center when the following occurs:

The PCM detects that there is a problem with the electrical charging system. The IPC receives a class 2 message from the PCM.
If the tachometer is less than 500 RPM and the power mode state is in the crank mode then this message will not be displayed. Instead the CHECK GAGES indicator will illuminate.
HIGH VOLTAGE
The IPC illuminates the HIGH VOLTAGE indicator in the message center when the IPC detects that the ignition is in RUN and battery voltage is greater than 15.75 V for more than 5 seconds.

LOW VOLTAGE
The IPC illuminates the LOW VOLTAGE indicator in the message center when the IPC detects that the ignition is in RUN and battery voltage is less than 10 V for more than 5 seconds.

Bill

 

Had the same problem after my alternator bracket was powdercoated. You moght try grounding the alternator case DIRECTLY to the front driver's side ground post. This fixed it for me....worth a try before you spend more time and money troubleshooting ! I spent weeks....

 

I'm to lazy to read through Bills reply, but inspect the wire harness and connector going to the alt for damage.

 

AUTO TAPPED the C5 and was able to retrieve only the codes as follows:
1638: Generator F terminal circuit
1637: Generator L terminal circuit

Recorded on AUTO TAP that the ALTERNATOR/GENERATOR output was indeed 0. Corresponding with every other piece of electrical equipment I utilized.

What next? Anyone?

 

My '04 Z06 displayed this a month ago. I guess I was lucky because I replaced the battery with an Optima Red Top, and I have not seen the error code since.

When this happened I researched the forums and came across this link:

http://forums.corvetteforum.com/show...post1557419423

Read Evil Twins response. I hope it helps. Good luck!

If our cars don't run right...then we don't run right.

 

Check the wire that goes from the alt to the starter. This wire can short out causing the problems you describe.

Ron

 

Here is the diagnostic info that goes with those two codes. If you read them you will see the PCM turns off the alternator if a problem is detected on the F terminal.

DTC 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.
Action Taken When the DTC Sets
The PCM will not illuminate the Malfunction Indicator Lamp (MIL)
The PCM will store the conditions present when the DTC set as Fail Records data only.
Conditions for Clearing the MIL/DTC
The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
The DTC can be cleared by using the scan tool Clear DTC Information function.
Step
Action
Yes
No

Schematic Reference: Starting and Charging Schematics

1
Did you perform the Engine Electrical Diagnostic System Check?
Go to Step 2
Go to Diagnostic System Check - Engine Electrical

2
Install a scan tool.
Start the engine.
With a scant tool, monitor the DTC information for DTC P1638 in Engine Controls.
Does the scan tool indicate that DTC P1638 has passed?
Go to Testing for Intermittent and Poor Connections in Wiring Systems
Go to Step 3

3
Turn ON the ignition, leaving the engine OFF.
Disconnect the generator harness connector.
Connect a test lamp to battery positive voltage and repeatedly probe the generator field duty cycle signal circuit in the harness connector while monitoring the GEN F-Terminal Signal on the scan tool.
Is the Generator PWM display affected?
Go to Step 5
Go to Step 4

4
Test the generator field duty cycle signal circuit for a short or open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 8
Go to Step 6

5
Inspect for poor connections at the harness connector of the generator. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 8
Go to Charging System Test

6
Inspect for poor connections at the harness connector of the PCM. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 8
Go to Step 7

7

Important
The replacement PCM must be programmed. Refer to Powertrain Control Module (PCM) Programming in Engine Controls 5.7L.


Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement in Engine Controls 5.7L.

Did you complete the repair?
Go to Step 8
--

8
Review and record the scan tool Fail Records data.
Clear any DTCs.
Operate the vehicle within the Fail Records conditions as noted.
Using a scan tool, monitor the Specific DTC info for this DTC.
Does the scan tool indicate that this DTC failed this ignition?
Go to Step 2
System OK

DTC P1637
Circuit Description
The powertrain control module (PCM) uses the generator turn on signal circuit to control the generator. A high side driver within the PCM allows the PCM to turn the generator ON and OFF. When Generator operation is desired, the PCM sends a 5 volt signal to the voltage regulator via the generator turn on signal circuit. This causes the voltage regulator to begin controlling the generator field circuit. Once the Generator is enabled by the PCM, the voltage regulator controls generator output independently of the PCM by monitoring the battery positive voltage sense circuit. Under certain operating conditions, the PCM can turn Off the generator by turning Off the 5 volt signal on the generator turn on signal circuit. The PCM has fault detection circuitry which monitors the state of the generator turn on signal circuit. If the fault detection circuit senses a voltage other than what is expected, this DTC will set. The voltage regulator also contains fault detection circuitry. If the regulator detects a problem, the regulator will ground the generator turn on signal circuit, pulling the voltage low. This also causes the PCM to set the DTC.

Conditions for Running the DTC
Key ON Test
The Key is in the ON position for 5 seconds.
The engine is OFF.
Engine Run Test
The engine is running.
The engine speed is less than 3000 RPM.
Conditions for Setting the DTC
Key ON Test
The ECM detects a high signal voltage on the generator turn on signal circuit for at least 5 seconds.
The engine must be started.
During the RUN test, the ECM detects a low signal voltage on the generator turn on signal circuit for at least 5 seconds.

Action Taken When the DTC Sets
The ECM sends a class 2 message to the IPC to illuminate the charge indicator and/or turn on a message.
The ECM will not illuminate the malfunction indicator lamp (MIL).
The ECM will store the conditions present when the DTC set as Fail Records data only.
Conditions for Clearing the MIL/DTC
The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
The DTC can be cleared by using the scan tool Clear DTC Information function.
Step
Action
Value
Yes
No

Schematic Reference: Starting and Charging Schematics

1
Did you perform the Engine Electrical Diagnostic System Check?
--
Go to Step 2
Go to Diagnostic System Check - Engine Electrical

2
Install a scan tool.
Turn ON the ignition, with the engine OFF.
Wait 5 seconds.
Start the engine.
With a scant tool, monitor the DTC information for DTC P1637 in Engine Controls.
Does the scan tool indicate that DTC P1637 has passed?
--
Go to Testing for Intermittent and Poor Connections in Wiring Systems
Go to Step 3

3
Turn Off the engine.
Disconnect the generator harness connector.
Start the engine.
Measure the voltage between the generator turn on signal circuit and ground.
Does the voltage measure near the specified value?
5.0 V
Go to Step 5
Go to Step 4

4
Test the generator turn on signal circuit for a short or open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 11
Go to Step 5

5
Test the generator battery positive voltage sense circuit for a high resistance or open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 11
Go to Step 6

6
Test the generator battery positive voltage output circuit for a high resistance or open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 11
Go to Step 7

7
Inspect for poor connections at the harness connector of the generator. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 11
Go to Step 9

8
Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 11
Go to Step 10

9
Replace the Generator. Refer to Generator Replacement .

Did you complete the replacement?
--
Go to Step 11
--

10

Important
The replacement PCM must be programmed. Refer to Powertrain Control Module (PCM) Programming in Engine Controls 5.7L.


Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement in Engine Controls 5.7L.

Did you complete the replacement?
--
Go to Step 11
--

11
Use the scan tool in order to clear the DTCs .
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC reset?
--
Go to Step 3
System OK

Bill

 

One thing to remember when you get fault codes. They do not tell you what is bad they only tell you where an out of tolerance condition exists. The reason for that out of tolerance condition may not be located at the place the fault code shows up. That is why the theories of operation and diagnostic procedures need to be understood. The diagnostic codes listed at various places on the web without the supporting data do little to provide that understanding and are incrementally better than useless.
Bill

 

Happy New Year to All!!

Thanks to everyone who has put in their 2 cents, and especially to Bill for his $2 (as opposed to 2 cents! ) Reading that it now makes sense to me how the alternator could be working for the Pep Boys but not when plugged into the system....the PCM has shut it down.
I will run through your suggestion tomorrow Bill. Thanks again....what a great place to hang out!
Oh yea....one more thing Bill. Where are you getting all of this? Is it available in the Vette shop manual?

Ron

 

Yes, all of this info is in the service manual

Some people complain that the $120 price is to high but once a problem like yours comes up that price seems cheap.

 

I picked up a DVD on the web that had the service manual and everything.....but soon after it became obsolete as I believe it linked into one of GM sites that became subscription(?). So I have asked Fred Beans for a copy......but they thus far were out of stock. Thanks.

 

Your DVD SEEMS like it links to the web, but it really links to an IP address which is different. You can enter the IP address given you when you installed the DVD in your address bar and it will access the service manual ON YOUR HARD DRIVE without even being on line. There are links on the manual to GM, but don't use them, they are for dealers. You can search the manual by year of car or enter the VIN number and it will call up your specifics. Once you've entered the VIN one time, if you just put in the first digit, the drop down box will come up and you can select your vin without re-entering all the digits. It's not the best way, but that's the way the DVD's were written, to access them by IP instead of by file name. You can also save the IP as a favorite and just click on it (named whatever you like)

 

there is a TSB covering wire chaffing on the fuel rail bracket(dr's side near the firewall)

this has a caused a few problems in the past

 

Thanks Steve and Jack. I appreciate all of the help. Especially now knowing that my DVD should still work. i thought that perhaps I had bought something that was on its way out....thus the low price. Happy New Year.

Ron

 

BadMedcn,
I purchased my DVD from a person on the forum. After a few set up problems with my computer and CD/DVD drive I was able to install it. It works as described above.

Bill

 

Gentlemen,

As described in Bill's post I followed the instructions and this is where I am: Using light hooked to battery POS,

First harness pin: Light "on", AUTO TAP F Terminal '0'
Second harness pin:Light "off" and F Terminal '0'
Third harness pin: Light "off", F Terminal '0'

Per instruction...this suggests a connector or wire issue.

A while later, same routine as above but here is what happened:

First pin: Light "off", F Terminal '0'
Second Pin: Light "off", F Terminal '1'
Third Pin: Light "off", F Terminal '0'

I suspect bad wiring but after unwrapping everything to the firewall the wiring looks healthy. Any ideas? What say you Bill?

Ron

 

just had the same problem, same codes even... It was the starter connections, it looked to be tight but it wasnt. Thats not it either the bolt from the starter was cracked off, you might wana check that.

 

I had the "Charge System Fault" this morning. At idle, heater fan wide open. I looked at the voltage and it looked fine. It went away after a few seconds.

BadMedcn, let me know what you find. I will be checking the starter wiring and grounding out.