PCM communication problem
PCM communication problem 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 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
Launching!
Joined: Jan 2012
Posts: 216
Likes: 1
From: Davisburg, MI
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.
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?
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?
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 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
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.
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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.
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Verdad Gallardo 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.
So it is really a problem with my PCM. I find it weird though that otherwise the car seems to run fine.
