So my van went into limp mode a couple months ago. I can only use 2nd and 3rd gear and have to manually shift between them. Service Light immediately came on. Trying to find someone to read the codes was impossible since it has the "OBD 1.5" system. Finally paid a garage to diagnose it. They found Code P1640 Quad Driver Module 1 error. They dug a little deeper and determined that the ground circuit was on all the time on the Purge Solenoid and on the TCC and said that the PCM was shot. Well I just got back from pick and pull and put a used one in there: SAME PROBLEM!! ... reacts just like when I pull the battery to reset it: Starts fine without service light then service light pops up about 5 seconds in, every time. I am out of options and patience. I know the QDM1 controls the TCC, Purge, and the Boost solenoids. Can someone please help?

if you can get a diagram of those controls, they are likely hooked together inside the pcm and one of the control circuits is likely shorted to ground somewhere

Thanks for the reply.... I tested the purge sel. and it looks good. Also getting good voltage from the PCM. I am testing to pins on the transmission control plug to see if anything is shorted out. I will let you know.