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Old 03-08-2015, 07:17 PM   #51
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Yes, that is how code 56 would be presented.
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Old 03-08-2015, 07:22 PM   #52
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New ECM should be an easy swap, as long as the PROM is transferred over, given that you have that code for a Quad Driver B Module failure, you are going to need a factory Service manual, and you need to find out what devices are controlled by that QDM B, it could be any one of up to four devices, there may be a short, or an open circuit in one of them, if so then you may not need to replace the PCM, just find/fix the short, or open circuit.
Factory Service manuals can be costly, but are good to have, their may be some for sale on E-Bay, give it a day or so to see if anybody here has access to one first though.
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Old 03-09-2015, 12:20 AM   #53
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That sounds like a true pain in the a%%
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Old 03-09-2015, 03:05 AM   #54
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If it was swapping the ECM and PROM that is easy, as for chasing the short, or open circuit, that is not as hard as it sounds if you can get the FSM, without an electrical diagram of the ECM/Quad Driver Modules it will be pretty much impossible.
You may get lucky and fix it with a new, or used ECM, but there is a chance the problem will still be there unless all modules running off of that QDM are checked out.
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Old 03-09-2015, 06:00 AM   #55
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Check the trans fuse in the fuse panel.

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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
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Old 03-09-2015, 08:10 PM   #56
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How about this as possibility? I researched for hours last night and found out one of the devices this controls is the EGR valve.
Now, this whole problem started when my Catalytic clogged. So I am now wondering if the backup of exhaust into the motor may have damaged-clogged the EGR?
I just inspected the EGR and it appears to be stuck in the somewhat up position. I am sort of assuming it should close completely when power cuts off?
Given that the car always flips out when I gas it into passing gear, it seems to make sense that the EGR opens to max when you do this and maybe its sticking? I mean this is the orig with 172K on it. Thoughts???
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Old 03-09-2015, 08:28 PM   #57
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Possible, but you'd get a code for EGR.
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Old 03-09-2015, 09:05 PM   #58
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I was just looking through the OBD1 codes list, and I can find codes regarding Open/Short conditions of the EGR, but nothing regarding the EGR not responding as there is with OBD2. EGR is really emission controls, but if it is open when it shouldn't be, it'* essentially a vacuum leak, where the engine is ingesting its own exhaust.

My guess would be to get the EGR closed, and take a drive with it unplugged to see how the car drives.
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Old 03-10-2015, 12:40 AM   #59
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If that EGR Pintle is stuck clean it till it is no longer stuck, then see how it runs, just be sure to replace the EGR Gasket.
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