V1 charging system woes - alternator issue

[Goblinfanclub1234]

2008 ss/tc donor

- new battery
- new alternator
- alternator cable to starter is good
- all fuses are good
- alternator has a good ground to the engine (I sanded all of the mating surfaces)
- engine to frame has a good ground

So I am measuring 12.80 volts at the battery when the car is off and around 12.24 volts when the car is running.

With the car running at idle I unplugged the alternator control wires and measured 11.04 volts across the two wires.

Does anyone know what the control voltage should be for the alternator to be putting out 14 volts? I read somewhere that the BCM looks at battery voltage as well as voltage in ignition circuit #1 for alternator control. I am running a push button start because the key ignition would not crank the engine, so perhaps I am having an issue with ignition circuit #1 voltage?? Anyone know if the theft module can disable the alternator?

I just ordered the service manual maybe it will have some info on the alternator control wire voltage range.

 

[Gtstorey]

If you get the oem service manual, it should walk you through the diagnostic steps.

 

[Rttoys]

Running and Charging should be between 13.8-14.2v.

Alternator case is ground. The big terminal is your output. That should read 13.8-14.2v when running and battery voltage when off.

The side connector has 2 wires; one is the 12v trigger controlled by the ecm and the other is a feedback wire to the ecm. The trigger wire should read 12v when running.

Make sure the big output wire goes to the starter. That wire continues to the fuse box on the Dr side and from there goes to the battery positive up front. All of those big wires may join at the starter, i for get, but they all join.

 

[Gtstorey]

I read through the oem description (2010 service manual, 08 is probably the same) of the charging system and it said that the controls wires were 5v pulse width modulated.

 

[Gtstorey]

There are also several DTC's related to the control circuit so you might want to check the trouble codes.

 

[Goblinfanclub1234]

There are also several DTC's related to the control circuit so you might want to check the trouble codes.

I checked with both tech2 and hptuners and I have no DTCs regarding the charging system.

I have a custom control panel I built for my intercooler fans and heated seats with a fuse panel and several relays, I am taking power from the post on top of the fuse box and ground from the rear driver side ground lug. I think this might be shorting somewhere...but not entirely sure.

 

[Gtstorey]

There is always the possibility of a bad "new" alternator, especially if it actually remanufactured. The return rate on remanufactured alternators is high.

 

[Robinjo]

There is always the possibility of a bad "new" alternator, especially if it actually remanufactured. The return rate on remanufactured alternators is high.

That's nice to know for the future..... buy only a new alternator.

 

[Gtstorey]

That's nice to know for the future..... buy only a new alternator.

At least be prepared for them to be bad. I'll still buy them because I'm cheap.

 

[escapepilot]

I almost want to buy a reman one at the local auto parts box store and ask them to test it before leaving just to see the look on their face.

 

[Goblinfanclub1234]

I had my alternator tested at the parts store and it was putting out 130 amps. I have ordered a replacement voltage regulator I am going to throw that on there and see what happens.

disconnected my added relay panel and the problem still persists, I knew I wired up my panel correctly.

ECU control wire sending 11.4 volts to the voltage regulator, I wonder if this should be 12 volts or if 11.4 is enough. I may replace the control wire connector next.

I REALLY REALLY HOPE THAT I DO NOT NEED A NEW BCM SINCE I ALREADY PAID TO HAVE THE ODOMETER RESET.

 

[ctuinstra]

From the service manual:

The engine control module (ECM) uses the generator turn on signal circuit, or L-terminal circuit, to control the
load of the generator on the engine. A high side driver in the ECM sends a voltage signal to the voltage
regulator. This signals the voltage regulator to turn the field circuit ON and OFF.

The ECM monitors the state of the generator turn ON signal circuit. The ECM should detect low voltage on generator turn on signal circuit
when the ignition is ON and the engine is OFF, or when the charging system malfunctions. With the engine
running, the ECM should detect high voltage on the generator turn on signal circuit.

The engine control module (ECM) uses the generator field duty cycle signal circuit, or F-terminal circuit, to
monitor the duty cycle of the generator. The generator field duty cycle signal circuit connects to high side of the
field windings in the generator. A pulse width modulated (PWM) high side driver in the voltage regulator turns
the field windings ON and OFF. The ECM uses the signal to determine the generator load on the engine. This
allows the ECM to adjust the idle speed to compensate for high electrical loads. The ECM monitors the status of
the generator field duty cycle signal circuit. When the ignition switch is in the RUN position and the engine is
OFF, the ECM should detect a duty cycle near 0 percent. However, when the engine is running, the duty cycle
should be between 5-99 percent.

 

[Gtstorey]

Yes I just re-read the manual and the above is correct.

 

[Rttoys]

There is always the possibility of a bad "new" alternator, especially if it actually remanufactured. The return rate on remanufactured alternators is high.

A “new“ part does not mean a “good” part. And those will kick your butt.

it may not be the case here, but it’s a saying you need to remember.

 

[Gtstorey]

System test procedure

 

[Goblinfanclub1234]

One eBay alternator and alternator cable later and I'm sitting at 14.3 volts. Time to go rip.