Quote:
Originally Posted by Blue Bowtie
With the older GM ECMs the error codes are stored in memory for the last 50 engine start/run cycles. Once a fault has been repaired, the codes will erase after that occurs.
As for the quad driver outputs in the ECM, they are monitored for open circuits, shorted circuits, and voltages outside the allowable range. Those outputs operate things like the EVAP vent and purge solenoids, TCC lockup solenoid or other transmission shift solenoids, EGR vacuum solenoid, cooling fan relay, A/C clutch relay, and any other options. Shorted or open wiring, disconnected solenoids or relays, or solenoid/relay faults are common problems causing these codes.
Your factory wiring diagrams should indicate which loads are connected to QDM A (code 26) and QDM B (code 56).
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Excellent summary. Thank you for that Blue Bowtie.
After I replaced the cam sensor and undid the neg battery terminal overnight, all the codes were erased when I did the first scan but 26 and 56 returned on subsequent scans.
I have already checked for continuity on all of the wires from the junction on the inner fender to the PCM. I will have to read back to see what other tests I completed back then. I am preparing myself to go through the whole list of component and circuit tests the best I can with test light and multimeter.
Yes, the GM Service Manual does have nice diagrams and text indicating the components controlled by each QDM. I will study that. This could be a nig pie to eat. I need to settle down and go one bite at a time.
Thanks again.