alternator overcharging
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1st Gear
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alternator overcharging
Dealer has replace the alternator 3 times, under warranty. It is putting out 15-15.8 volts. Displays system charge fault, the abs and traction control light up and don't work. Took it back again same problem, now they are saying that it is the pcm. Has anyone had this problem?
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Your alternator uses a VOLTAGE reference wire to control the alternator output voltage.
Examine the schematic below:
The RED wire that connects on the starter solenoid and runs up to the alternator connector pin "D" must be at battery voltage potential. You will also see that it has a fusable link in that wire. With the engine OFF, disconnect that connector on top of the alternator and measure pin D to chassis ground. You should see full battery voltage on that pin.
The BATT terminal on the back of the alternator should also have full battery voltage on it.
That red wire is what the alternator uses to control output. If it is LESS than battery voltage, the alternator regulator will continue to increase battery voltage until it either reaches the normal output or goes to maximium output.
Here is where it connects to the starter solenoid and where the fusable link is:
Examine the schematic below:
The RED wire that connects on the starter solenoid and runs up to the alternator connector pin "D" must be at battery voltage potential. You will also see that it has a fusable link in that wire. With the engine OFF, disconnect that connector on top of the alternator and measure pin D to chassis ground. You should see full battery voltage on that pin.
The BATT terminal on the back of the alternator should also have full battery voltage on it.
That red wire is what the alternator uses to control output. If it is LESS than battery voltage, the alternator regulator will continue to increase battery voltage until it either reaches the normal output or goes to maximium output.
Here is where it connects to the starter solenoid and where the fusable link is:
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From: South Western Ontario
FYI, the PCM provides that turn-on signal and the alternator provides that PWM signal back to the PCM. The PCM just turns the alternator on and off. It does not control the voltage.
The dealer is likely saying PCM because the tech sees the wires going to the PCM. When there is something wrong that appears electrical the tech just starts replacing every part that has a connection. So, alternator swapped without luck means the PCM must be bad. They might suggest the starter next (even though the solenoid post is just used as a connection block). A lot of techs have no clue how to actually troubleshoot. Test for bad wiring? Good luck having that happen.
It's possible you have multiple issues, but at least get the alternator producing the correct voltage before worrying about other things which might be wrong.
The dealer is likely saying PCM because the tech sees the wires going to the PCM. When there is something wrong that appears electrical the tech just starts replacing every part that has a connection. So, alternator swapped without luck means the PCM must be bad. They might suggest the starter next (even though the solenoid post is just used as a connection block). A lot of techs have no clue how to actually troubleshoot. Test for bad wiring? Good luck having that happen.
It's possible you have multiple issues, but at least get the alternator producing the correct voltage before worrying about other things which might be wrong.
Last edited by lionelhutz; Dec 5, 2012 at 12:54 PM.
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From: Somers, CT and Clermont, FL
St. Jude Donor '09-'10-'11-'12-'13-'14-'15-'16
The PCM provides the Field Duty Cycle Signal, which is used to control the output voltage of the alternator.
The Field Duty Cycle Signal is a precise Pulse Width Modulated control of the alternator field turn-on. The PCM determines the duty cycle, based on the voltage reference signal it receives.
The bottom line here is yes, the PCM controls the alternator output voltage on C5 Corvettes.
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From: South Western Ontario
Tech Contributor
Joined: May 2008
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From: Somers, CT and Clermont, FL
St. Jude Donor '09-'10-'11-'12-'13-'14-'15-'16
I was incorrect stating that the PCM sends the field duty cycle signal. The PCM only monitors the signal for charging system faults. The actual field duty cycle signal originates from the internal voltage regulator in the alternator.
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From: South Western Ontario
Yes, I already knew the schematic was correct. I've read about how the PCM can control the charging on some of the GM products (actually most new GM products now I believe), but not on this car.
Here is some good info on the charging system.
http://forums.corvetteforum.com/1558326606-post9.html
Here is some good info on the charging system.
http://forums.corvetteforum.com/1558326606-post9.html
