Scan9495 Observations?
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Joined: Jul 2010
Posts: 1,520
From: Born on the Florida West Coast, now where can I retire?
Re: Scan9495 Observations?
Another piece of the puzzle, possibly pointing to the PCM.
In several instances, the end of the defective data line shows DTC 86. I assumed this was just a bogus code, because it isn’t referenced in the factory manual. But I did a Google search on GM OBD1 Trouble Code 86, and found it is a code (at least in some other vehicles) for:
https://repairpal.com/gm-obd-code-86
KYWes: is the engine experiencing any noticeable “hiccups” that might correspond to these data faults.
In several instances, the end of the defective data line shows DTC 86. I assumed this was just a bogus code, because it isn’t referenced in the factory manual. But I did a Google search on GM OBD1 Trouble Code 86, and found it is a code (at least in some other vehicles) for:
https://repairpal.com/gm-obd-code-86
KYWes: is the engine experiencing any noticeable “hiccups” that might correspond to these data faults.
Prominent Member
Joined: Jul 2010
Posts: 1,520
From: Born on the Florida West Coast, now where can I retire?
Re: Scan9495 Observations?
If you can run another scan with the Comms screen enabled, save the Comms screen results to file, and post it, I may be able to see if the PCM is issuing a correct checksum for the bad data. That would really put the blame on the pcm's internal operation.
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Joined: Mar 2003
Posts: 449
From: Louisville, KY
Re: Scan9495 Observations?
Gary, here's the Comms data you asked for. I haven't reviewed it yet but when I was logging this run I didn't see the DTC flash red so I'm wondering if the car is being a kid going to see the doctor.;-)
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Joined: Jul 2010
Posts: 1,520
From: Born on the Florida West Coast, now where can I retire?
Re: Scan9495 Observations?
The problem does show up in this file. The data is being shifted one space to the right randomly early in the data string. I don't know what is causing that, but I doubt it is caused by the pcm. It could just be some electrical noise on the data line or the 12v power to the pcm, a bad cable, or a bug in the program. But I haven't seen that symptom too much before this. The program correctly fails the line with a bad checksum message and restarts the process. Apparently the program does not discard the bad data however. I will look into that.
Thread Starter
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Joined: Mar 2003
Posts: 449
From: Louisville, KY
Re: Scan9495 Observations?
Gary, wondering if you've had time to research this?
The problem does show up in this file. The data is being shifted one space to the right randomly early in the data string. I don't know what is causing that, but I doubt it is caused by the pcm. It could just be some electrical noise on the data line or the 12v power to the pcm, a bad cable, or a bug in the program. But I haven't seen that symptom too much before this. The program correctly fails the line with a bad checksum message and restarts the process. Apparently the program does not discard the bad data however. I will look into that.
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Oct 20, 2003 10:40 PM