Code 56 on 93 regal

A quad driver is what turns the fuel injector on and off. They're part of the PCM and are not replaceable separately. You have to buy a rebuild PCM. BUT, do not do that until you find out WHY the quad drivers went bad. Usually it's caused by a short in the fuel injector coil windings or a short in the harness. If you don't fix it and just replace the PCM, you'll burn out the new PCM

A quad driver is a transistor in the engine control module ! GM OBD Trouble Code 26 GM OBD Trouble Code 28

Code 26 is for a problem with one of the quad drivers inside the engine computer, or the wiring harness, and code 42 is for a problem with the ignition module or the control.
You'll need a shop manual with the testing procedures for each code to proceed.

quad driver A fault
ECM module have input and ouput, quad driver are there to activate a solenoid or relay
quad driver A drive a few of those output
example quad driver A control canister purge solenoid and the solenoid is defect . the quad driver will kick off until you change the solenoid
there is two kind of driver 1984 to .......one will reset if trouble is repair
the other one is the ecm module itself have to be change after is repair .....(quad driver act has a driver or big fuse)

code 26 is .... Quad Driver Module (QDM A) error

I will start by pinout check current + to ECM and - ground there is many .
A Quad driver work like a big fuse d?pends some are resettable and other not reset(ECM defect) if it is so then you have to check all solenoid not short to ground before replacing ECM it will burn without checking the solenoid
hope it help

Try the ignition control module... QDM stands for quad driver module which is apart of ignition control module. This module is located on top of the engine under the coil cover. Where the wires plug-in, this is the module.

Try the ignition control module... QDM stands for quad driver module which is apart of ignition control module. This module is located on top of the engine under the coil cover. Where the wires plug-in, this is the module.

The quad drive is in the PCM (Power Control Module) NOT the Electronic Control Module (ECM)

The quad driver is in the computer it drives the fuel injecters. you could have an injector problem if one injector shorts it will cause the code to show up you can ohm the injectors and find the problem e-mail me and let me know what you find Phil