I'm trying to diagnose a problem with my 97 Olds Aurora, it's throwing code P1376 (PCM Ground Circuit fault). Problem I have is that it requires a Scantool 2 to chase things down, and I don't have access to one of those.

What I'm hoping to find is info on which wire leaving the computer is supposed to be the PCM ground, so I can follow it from that point with a multimeter to verify conductivity.

I've already looked at some online resources (Mitchells on Demand) and I can't make heads nor tail of the wiring diagrams.

Previously posted here
http://www.chevelles.com/forums/showthread.php?t=104379&highlight=gm%2Fcaddy%2Folds , local dealer is no help, just wants me to bring it in for them to troubleshoot for large $$$ per hour.



Thanks guys!

Sid

i don't know if this will help or not but i have a 95 buick on all data and it shows the pcm ground at terminal PA2 at the pcm(black/white wire), it goes to the data link connector pin A and also to ground. Also pin PA1 (tan/white wire) at pcm goes to ground. If the wire colors match up at those terminals maybe this will help some. The pcm also provides sensor grounds at terminals
PB2,& PB1

DTC P1376 Ignition Ground Circuit



G101
Lower RH rear of Engine, below Power Steering Reservoir
hope this helps.

Circuit Description
The PCM applies 2.5 volts on the Ref Lo voltage (CKT 453) circuit to the Ignition Control Module. Ref Lo voltage to the PCM represents the voltage difference between Ref Lo and the PCM power ground. This is needed to ensure that the PCM and IC module signals all have the same ground reference. If the Ref Lo input voltage goes too high or low, DTC P1376 will set.

Conditions for Setting the DTC
Test Condition
DTC P0560 is not set.

Failure Conditions
Ignition Control Module Ref Lo input is + 1.4 volts or greater for 1 second. OR
Ignition Control Module Ref Lo input is - 1.01 volts or less for 1 second.
Action Taken When the DTC Sets

The Malfunction Indicator Lamp (MIL) will not illuminate.
No message will be displayed.
Conditions for Clearing the DTC

A History DTC will clear after forty consecutive warm-up cycles with no failures of any non-emission related diagnostic test.
A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.
Use a scan tool to clear DTCs.
Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Clearing Diagnostic Trouble Codes in PCM Description and Operation.
Diagnostic Aids
This DTC may set due to an improperly installed PCM. This may cause the PCM to not be electrically isolated from the body ground.

Using the scan tool the normal average Ref Lo voltage displayed is 0.00 volts + or - 0.20 volts.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.

If the snapshot ignition ground voltage is 1.1 volt or less, this means that the PCM ground voltage is floating high causing P1376 to set.

Voltage measured at ignition control module connector C4 terminal F should be less than 0.1 volt. If the voltage is higher, then the module must have a bad ground causing the module to try to ground through the Ref Lo input to the PCM.

DTC P1376 Ignition Ground Circuit



G101
Lower RH rear of Engine, below Power Steering Reservoir
hope this helps.



I show G117 same location.. Sid there are several splices... I'd try wiggling around on harness and see if you can get the light to set or watch your meter. Also look for broken wires where pins terminate. If you really need diagrams I can send them in word format. PM me if you want em.

Thanks=you guys ROCK! I really appreciate the help!