LeSabre 1993 - Code 56 Quad Driver Module B Fault

[LeSabre93]

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

[HotZ28]

Originally Posted by gm_classic

The code is related to your cooling fan, egr and tranny controls. But you mos likely have a bad crankshaft sensor.

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[HotZ28]

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.

[LeSabre93]

Thank you HotZ28,

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