Hi,
I tried to post this in hybrids but not much luck besides a helpful member who tried to see if I did the basic steps of trouble shooting. Here goes my problem:

I have a 1999 4.8 with a 4L60E RWD and the computer coming from the 4.8.
These all are installed into a GM D-body. I also have an electric fan.
The car runs, for the past three weeks I have been using it every day the weather is nice.
The problem is I cannot communicate with the PCM when I try to plug an OBDII scanner. I have tried it with two scanners. I have the OBDII plug out of a 1999 truck so the pins are at the same locations. I checked that I have two grounds on pins 4 and 5, battery + on pin 16 and data signal on pin 2. I get an error when I plug the scanner.

How can I know I get a signal on pin 2 from the PCM?
What is the voltage I should get on pin 2?
How can I make sure the PCM works properly?
Can the car run fine but the circuit for the OBDII communication be damaged?
I read that one sign the PCM gets damaged is when the fan starts with the key on. I remember once the fan kicking in when I just started the engine and I found that weird. But it only did it once and everything seems to run fine.
Any tips?

Thanks

 

I had a similar problem on an LT1 swap. One of those ground pins on the OBD2 connector must be connected directly to a specific ground coming from the PCM harness.

I hope you are probing the signal wire with a high impedance volt meter for electronics. The car will run fine without providing communications to a scanner.

 

Thanks for the reply,
I will check again for the ground but I don't remember seeing that information. I only read until now that it has to be a good ground but that's it.

I am not sure what kind of voltmeter I have. I will verify that also.

But is there any way to know if the problem is from the computer being fried or is it just a programming glitch?

If I probe the signal wire and if the computer is fine what shoud I read on my voltmeter?

 

If your volt meter has a needle on it, do NOT use it. Nor a cheap digital with less than ten mega-ohms impedance.

 

Thanks,
I will check the impedance on it. It does not have a needle.

I'll also try the trickle charger tip tonight. Haven't heard of that one yet, I just read about it.

 

I tried the charger thing....doesn't work

This is also the meter I am using:

http://www.mtpinc.com/Products.htm?NL=1&CD=78&ID=217

Any ideas what else I should try or should I go for anoter PCM?

Thanks

 

Have you tried your scanner on another vehicle? Do you know anybody with a '99 through '02 4.8, 5.3, or 6.0L truck, or '99 through ' 02 LS1 car? If it communicates with their vehicle, try plugging your PCM into their vehicle to see if it communicates. Don't need to start it to test that.

 

I tried the scanner on my wifes's Vibe and it worked. I also tried another scanner on my car and it did not work. Unfortunately I don't know anyone with a truck or car, I was thinking of trying something like that.

 

I was finally able to try another PCM. The scanner connects to that one.
So it is really a problem with my PCM. I find it weird though that otherwise the car seems to run fine.