p1640 QDM 1 error....any ideas? ECM has been swapped already - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat

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Old 05-20-2008, 07:23 PM   #1
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Default p1640 QDM 1 error....any ideas? ECM has been swapped already

Well....cleared codes and went on a drive with the Ethos Snap-on Scanner. Neat little tool.

IAC counts never showed below 36.

Previous fault codes were p0341 and that never came back so we look good to go.

HOWEVER......the problem generally has been found...so I need to pick your brains to see whats up.

P1640--QDM-1 Failure. Quad driver module I presume in the ECM.

I already swapped the ECM. No way in hell could 2 be bad?

Also big thing.....I have a brand spankin' new battery in there. Volts show 13.6 or so....but when I turn the A/C on with the Lights on....voltage drops to 12.2!!

Could it be a faulty voltage regulator? Alternator?

How could the electrical cause the motor to not boost at all?

Timing looked excellent BTW....No more than 15 degree at WOT....ranged down to 27 or so. Car doesn't miss or anything. Just has no balls, no boost, crappy mileage, etc.

Thanks a ton!
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Old 05-20-2008, 08:14 PM   #2
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You need someone with a 94 FSM to tell you what four devices get power from QDM 1.

Since you're not getting boost we can take a stab in the dark & have you check the resistance of the boost control solenoid.

Have you pulled the rubber boots off the battery cables to check for corrosion on the cable ends? That'* the first place to look when the voltage is dropping.
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