LeSabre 1993 - Code 56 Quad Driver Module B Fault

This all started with the car not starting up at random times with NO error codes or service engine light. The engine would turn over, but not start. I replaced the fuel filter and spark plugs, with no success.

Then after a month I finally got the service engine light and an error code.

I erased the code, started it up and immediately got it back again with the service engine light ON. It's code 056 Quad Driver Module B Fault on my Actron CP9185.

The only electrical schematics I have are from the "Haynes Repair Manual Buick, Oldsmobile & Pontiac Full-size models 1985 thru 2000 Front Wheel Drive".

Any help is greatly appreciated!

George

The code is related to your cooling fan, egr and tranny controls. But you mos likely have a bad crankshaft sensor. Your post was closed for posting copyrighted alldata material! Read our guidelines concerning posting of copyrighted material.
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Now back to the original question! The Quad drivers are simply mini grounding relays built into the PCM/ECM. Each driver controls up to four devices. The DTC is set when the PCM/ECM detects an improper voltage level on a circuit connected to the QDM. DTC 56, or on most GM cars DTC (26) points to Quad driver “B” and that is used for the shift solenoid A & B, TCC PWM (apply) solenoid, EGR 1 & 2 solenoids, (if you have one). One of these solenoids is showing a improper voltage and may be stuck or grounded, drawing constant current, or the PCM/ECM is bad. :uhoh:

Thank you HotZ28, :smile:

It was the "shift solenoid A" which was giving an incorrect low voltage to the computer and causing the quad drive module B fault!

It has been replaced and all is well!

Thank you again very much for your help!

George