Last weekend, I replaced the vacuum harness on my LN2 because the lines that went to the EGR vacuum solenoid were broken. I last knew I had a CEL from THAT because there was no reading to the EGR vacuum solenoid or the EGR valve. So I've had a CEL going for several months. I replaced the vacuum harness, cleared out that code, then the IACV code came out (probably been throwing that code for a while too) so I replaced the IACV. And today it starts throwing yet ANOTHER code. I went to get my printout and it says "Quad Driver Module (QDM) B Fault". What the @!#$ is this quad driver module. I've never heard of anything like that before. The car runs just fine, it idles a little funny but it always has. Do any of you GM gurus know what the hell this thing is and why it's being faulty? Thanks




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Gm tech at work says could be a PCM, wiring to the PCM, or even an O2 sensor.

I just did some research beyond JBO and so far it looks like I have to replace the entire PCM itself. Any other outside opinions?




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Not unless you are an electronics whiz and know what your are looking at once you take it apart and know how to test every thing.

Better of just replacing it. Go to the junk yard and find a car with the same options, engine and tranny, take the pcm and use it. Hopefully it won't need to be programed.

All the 95 and 96 PCM's are the same if I remember right. I'll just swap the EPROM out of my PCM and stick it in the new PCM.




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Update... I called a local junkyard and picked up a "new" PCM today. I'll probably pull the EPROM out of mine and plug it into the new one considering I don't know what the PCM came out of, all I know is that it was a 95 Cavalier.




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it probably was the driver module INSIDE your PCM, if you look at your PCM, youl see a small cover held on with 2 torx bolts, there is a small "chip" or module in there, i belive that is your QDM

A quad driver is a small chip that regulates power to devices / sensors on the motor. Like the O2, TPS..etc. "Quad" as is 4 outputs to devices. When you get a quad driver fault, one or all 4 outputs are "out of range". A lot of electronics on these cars operate
on 1-5v dc, the particular output may be 0v, thus the "quad driver fault". It may be the chip, may be a wire shorted to ground, may be a sensor open and not returning a signal as there's several reasons this may occur. Hope that helps.
Don

Thanks Don. We'll see what happens when I replace the PCM




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Replaced the PCM today. I put my original EPROM in the new PCM I got from a junkyard. Took the car around the block, and BAM! Check engine light. Checked it, same damn thing. Anybody have any ideas?




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Sounds all too familiar. Had a "quad driver fault" on another GM car, early '90's i think. I replaced the computer, bam it was back within 10 minutes. I would up getting a wiring diagram from Helm, looked over the wires and the ECM connector and figured out that
the Quad "1" (that was the one bad on my truck) hooked into the temp sensor, the TPS sensor and a couple of others i can't remember right off hand. I traced the wires out and what do you know, one had a bare spot and was rubbing on the intake manifold thus "grounding" it. I fixed that and it went away. Wasted $149.99 on a new computer.
Hope that helps, my lesson was expensive as i replaced 3 computers before I figured it
out.
Don

Ouch that sucks. I'm really starting to get aggrevated with this because I want to get my car SOLD. Not to mention, I really don't feel like pulling everything back apart again...




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Ok so along the lines of this post, i have a question to ask?

Does anyone know what Device would cause a 26 QDM Fault B and 27 QDM Fault B? I have access to the factory manuals if needed, but I'd like to give the genusies here a go.