C5 Vette Dissassembly?

[lionelhutz]

Is there a C5 dis-assembly around anywhere? The C5 PCM is very picky about the alternator interface and I was hoping to see what the alternator tests are and possibly figure out why it throws a charging fault even when the connected alternator functions perfectly fine.

[LRT]

What DTC is being set ?

[lionelhutz]

It seems that P1637 or P1638 are the DTC codes for the charging circuit. There is also a error message that appears in the driver information system. I have found that the DTC's can be set to no error reported and the charging system error can still appear in the DIC.

People typically have issues with these cars popping up the error message on startup with a replacement alternator even though the alternator functions perfectly fine and after resetting the initial warning message it doesn't come back until the car is started again.

I was hoping to get some insight into why the PCM is so damn picky.

[LRT]

Not sure what year / OS you are working with. Not all platforms were wired the same with respect to the alternator. Some used only the alternator "L" terminal - often wired to a simple "idiot light". Others used both the alternator "L" and "F" terminals (Corvettes used both I believe).

If this is in an actual Corvette, make certain the alternator is wired as a Corvette would have been, and confirm the alternator you are trying to use has all of these terminals.

If this is not in a Corvette, you can turn off the P1638 DTC (Field Duty Cycle), and wire a bulb into the "L" terminal circuit.

[LRT]

I don't own a Corvette, but this seems to be a very common problem - based a quick Google search.

Here is one of many discussions that seemed relevant ....

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=3&cad=rja&uact=8&ved=0CDEQFjAC&url=http%3A%2F%2Fwww.corvetteactioncenter.com%2Ffo rums%2Fc5-technical-performance%2F35666-charging-system-fault.html&ei=X57GU8vDFcGWyATmw4GIBQ&usg=AFQjCNGDA7iw2rHeBfpyij7NNvwVwy0tLQ&bvm=bv.71126742,d.aWw

[lionelhutz]

Yes, all C5's used both L and F terminals. Ideas for troubleshooting a car aren't what I'm looking for. I'm looking for the specific testing the PCM does when it decides to make the charging system fault appear on the DIC to gain some insight into why certain replacement alternators cause an issue on startup.

[Fast355]

Yes, all C5's used both L and F terminals. Ideas for troubleshooting a car aren't what I'm looking for. I'm looking for the specific testing the PCM does when it decides to make the charging system fault appear on the DIC to gain some insight into why certain replacement alternators cause an issue on startup.

My guess would be aftermarket JUNK chinese regulator on the junk Autozone/Oreilly's/Krager/whatever . I bet if you had a NAPA Premium or better yet GM Delco/Delphi alternator it would not have an issue.

[LRT]

My guess would be aftermarket JUNK chinese regulator on the junk Autozone/Oreilly's/Krager/whatever . I bet if you had a NAPA Premium or better yet GM Delco/Delphi alternator it would not have an issue.

I think you have probably hit on the issue.

I don't own a Corvette, and don't know the answer. I did take a look at the service manual and it seems to point toward the regulator, as well as conductivity (i.e. quality grounds and connections) as contributory to this issue.

Overview attached below ...

[lionelhutz]

OK, the PCM monitors the F and L signals. I want to know exactly what the PCM is doing.

The service manual does not contain the information I'm looking for because it doesn't describe the PCM fault detection logic (you know, the exact tests, levels, timing etc in use - or a flow diagram for the piece of code that detects faults).

I can troubleshoot connection issues and failed alternators just fine. I can't troubleshoot this fault message that appears only on engine-start without knowing what the PCM is doing.

[LRT]

You may want to read the PDF that I posted.

The regulator can trigger the PCM setting both DTC P1637 and P1638 - as the regulator has its own internal diagnostics. The PCM can also trigger DTC P1638 on its own - based on the alternator duty cycle, which is controlled by the regulator.

So as proposed by Fast355 - a low quality regulator could well be at the heart of the issue.

[lionelhutz]

People have put $500 high output alternators made by a high end US manufacturer and still had the problem.

I want to know exactly what the PCM is testing for. Generalized descriptions of the system do not give enough details on how the PCM decides there is a fault.

[mecanicman]

In system options there are f/l terminal flags. Chage the 1 to 0 for the one causing you grief, disable the code, and dash light should shut off.

[lionelhutz]

As I already posted, you can turn the codes off to no MIL and no error reporting and the DIC will still show a charging fault message.

[mecanicman]

Yes, as I already posted, you have change the flag in system options to shut off the dic charging fault message in addition to the codes.

[lionelhutz]

That would disable the terminal? I wanted to know what causes the warnings to appear, not just disable the PCM monitoring terminals. It could be OK if the F-term circuit is disabled and just the L-term circuit is left as long as the L-term circuit doesn't cause any messages. Ideally, the L terminal needs to be left working so it can still be used to energize the alternator when the engine is started.

[mecanicman]

I dont think it disables the terminal, just the pcm looking for something from it(I dont know for sure). I have used this method when swapping engines/pcms between platforms and the alternator still charges, just no warning light.

[highlander]

You mean disable the 1637 or 1638 codes?