GM 3.8 p1640 code QDM error


Hero Member
May 30, 2008
I am working on a 94 Buick park avenue ultra, 3. 8 superchrged.
the car has a hesatation at about 3300 rpm and above
runs perfectly under 3000rpm
to make things even worse, the vibration dampener was broken causing all kinds of noise
I replaced that and all is quiet
This is where we are now. . . . .
I am using an otc genisys which is giving me the (p1640 code, QDM error), with possible causes being
evap circuit-
cooling fan circuit-
boost control solenoid-
pcm wiring. . . . .
Now those are from the fast fixes and common overlooked items. .
Has any of you all had QDM error and what did you find?

I am all over the board with this, just need a solid answer. . .
thank you


Jun 24, 2011
95 Buick Riviera Supercharged 3800 V6 engine.

I got this error fixed finally after two years, a half dozen garages, and a couple of thousand wasted on trying to get all the "knowlegable" mechanics standing around scratching their heads to fix it!!!

The P1640 error is the Quad Driver. . . However it only runs THREE devices.

1) Boost Control Solenoid
2) Torque Converter Clutch
3) Evaporator Purge Solenoid

Of course everyone wanted to replace my transmission or charge me a bundle to replace the TCC. . . Even after I explained I had no actual symptoms. . . Great shifts, gas mileage, runs GREAT! The ONLY problem was my "Service Engine Ligh" when ever I let off the accelerator. . .

When the owner told me to "come see me when the bolts are falling out of your transmission" I started researching the internet. . . Well this is actually a COMMON error. . . Replaced the PCM (the computer) THREE times. . . The 4th computer is in my Rivy now. . .

Of course it was the boost control solenoid which luck may have it is NO LONGER IN PRODUCTION. . . the part number is GM #12353309. AND it is called the "Supercharger Bypass Valve Kit". . . a small three inch device with three tubes, only two are connected to hoses and an electrical connection.

EASY fix once you know the problem! ONE nut and pop off the hoses and reconnect.

NOW. . . finding the part. . . did an internet search and found a place in Canada for $27. 00 but the dealerships are getting wise if they have the part they tried to charge me $75. 00!

GOOD LUCK! I wish I could scream this from the mountain tops after all the frustration, time, and MONEY wasted on this simple fix!

Michael Barcher


Dec 8, 2006
Well, normally, a replacement PCM, does fix the problem......but each leg of the circuits it controls, should be check out first.......check to see if the circuit actually works AND if the circuit is shutting down due to a high current draw.....the quad drivers have built in current detection......