OBD 2 port

Discussions about GM and aftermarket Engine management systems

OBD 2 port

Postby chevyken » Sat May 06, 2017 12:33 pm

Its been a bit over 2 years now. finally put some miles on my truck. I, still have not been able to get my OBD 2 port to link to the scan tool. I have gone over my notes, and pulled the wire straight from the ECM and nothing. My reader will look for it but then tell me to "turn ignition off for 10 seconds"

2004 engine and harness,
PCM C1 (blue),
Pin 59, Dark green
Circuit 1049 Class 2 Serial Data.

I for the life of me can not figure out why it wont link up, or why my MIL light hasnt came on yet. I know for a fact there are some missfire codes in there.

Any advise? Thanks
85 c10 85 c20 #longbedbadness
chevyken
 
Posts: 123
Joined: Mon Mar 23, 2015 11:26 am
Location: Brownsburg, In

Re: OBD 2 port

Postby Cornchip » Sun May 07, 2017 7:57 am

Just the other week, my 2007 Trailblazer left me stranded in the driveway with a 'no start' condition. I tried the starter and then the relay, proving that they were fine. My thinking went to the ignition switch and from what I have read, it will code when it does (I always have a light on with this thing). This is when I found out that I couldn't connect to the PCM through the OBD port (no PND2L lights as well). I had it towed in at this point and properly diagnosed. First they told me the bad news and said it needed a new PCM and a trip to a GM dealer for programming. They later called back to say it was my lucky day. The problem...a bad (going bad) 12v supply wire. Inside that wire it had corroded enough to cause enough resistance to drop the voltage to the PCM causing the no start. You can't check it easily with a volt meter either. The wire will pass a continuity test and also read system voltage with no load as well. The shop said they checked the harness supply lines with an old halogen head light bulb (4 to 5 amp draw) to quickly find the culprit. I'd imagine the same wire condition is true for the grounds as well. Either way, you can run a bypass back to the battery posts and isolate the suspect circuit. Don't know if this would apply for your problem, but I can say from personal experience....the wiring harness in my TB is crap.

Good luck, Clint
Cornchip
 
Posts: 153
Joined: Thu Mar 28, 2013 3:52 pm

Re: OBD 2 port

Postby chevyken » Sun May 07, 2017 5:50 pm

Cornchip wrote:Just the other week, my 2007 Trailblazer left me stranded in the driveway with a 'no start' condition. I tried the starter and then the relay, proving that they were fine. My thinking went to the ignition switch and from what I have read, it will code when it does (I always have a light on with this thing). This is when I found out that I couldn't connect to the PCM through the OBD port (no PND2L lights as well). I had it towed in at this point and properly diagnosed. First they told me the bad news and said it needed a new PCM and a trip to a GM dealer for programming. They later called back to say it was my lucky day. The problem...a bad (going bad) 12v supply wire. Inside that wire it had corroded enough to cause enough resistance to drop the voltage to the PCM causing the no start. You can't check it easily with a volt meter either. The wire will pass a continuity test and also read system voltage with no load as well. The shop said they checked the harness supply lines with an old halogen head light bulb (4 to 5 amp draw) to quickly find the culprit. I'd imagine the same wire condition is true for the grounds as well. Either way, you can run a bypass back to the battery posts and isolate the suspect circuit. Don't know if this would apply for your problem, but I can say from personal experience....the wiring harness in my TB is crap.

Good luck, Clint


Right on. I will pull power directly from the battery and see if that helps.
85 c10 85 c20 #longbedbadness
chevyken
 
Posts: 123
Joined: Mon Mar 23, 2015 11:26 am
Location: Brownsburg, In


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