I am trying to figure out what is wrong with a 1994 Bonneville naturally aspirated. It is my girlfriends car and she told me that on Friday after driving it fine to the store when she got back to the car and tried to leave it would not go into drive. She had to put it into 2nd and then after she got going she could put it back into drive. Been the same since. It wont go into 1st gear it seems. Took it to a shop and it coded P1670. The quad driver module #4 Circuit. The shop said it would take them days to diagnose the problem at their normal hourly rate and she should not drive it at all anymore or it is going to kill the transmission. She said the AC would come on and she used it that day for the first time in a few months. The mechanic said the cooling fans are functioning properly. If I drive it to my house from the mechanic shop roughly 10 miles would that hurt it? Anyone have any information on the components in the #4 circuit and how to test them etc?

Please do a search on P1670,. There is a lot of good info that is listed out. I remember back in 05 there was a lot of discussion.

Hey Bill, is that a 4t60 in that car? If so, I would check that vacuum line on the shift module.

Okay so after digging thru the forum this is what I found.
So first off am I going to ruin the transmission driving it? and how do I check the fan low and high speeds?

Cool, thanks for doing the legwork. Been a crazy day so far.

None of that appears to control the transmission. Which then makes us look for a little more info behind what the trans actually did. Did it seem to grab, not engage at all, slip, shudder, jerk.. what did it really do and does it do it when the selector is in Drive, 3, 2 and 1 as well as reverse?

It'* possible a forward band snapped, if so, the trans should try to move in 1 or 2. But then you mention is it going to hurt it by driving it..so then there'* confusion as to what'* actually wrong, if the fluid is up to the correct area on the dipstick and if the fluid looks reasonable.

Wouldn't go into drive...but then would.. meaning the shifter only? The band I describe above is a possibility as it'll get the car moving with the manual 1-2 band. Not going into 1 if the selector is in 2 is expected as I know for sure the 4T65 will start and stay in 2nd when it'* selected this way. I believe the 4T60 (your trans) is the same way.

Okay so here is exactly what it will do. Put it in drive and it will go into gear but will bog down so much the car will barely move. No shudders, no jerks it just wont really go like its trying to push something out of the way. Put it into 2nd the car will not bog down nearly as much and once you get going you can shift it up to drive and it goes fine. Reverse engages fine also. So will driving it like this cause damage? I am not thinking driving it all the time just to get it to the house to work on it.

I understand this is not directly associated with the transmission. But what I was told is that because it is the #4 circuit in the QDM thats what is causing the problems. I don't understand exactly how it all relates, but he said its the way GM built the QDM if this circuit is bad then it can effect the transmission. The transmission is from what everyone can tell completely fine its just the QDM causing issues.

I also found some information on testing for the p1670 DTC. Says to probe the PCM harness terminals WD12, WD10, WD11 and WD13 to try and isolate the problem. I have no idea what components those terminals point to.

Bill, what would the cause be if the transmission went into limp home mode? I remember something somewhere that if the trans loses the PCM, then it goes into limp mode, ie 3rd gear start out.

gms go into 3rd and stay when in limp home mode. unless something causes them not too. something broke with the 3rd gear part of the tranny.

From everything being described, I'm thinking the transmission has an interenal issue as well. QDM 4 and the code don't appear to have anything to do with the trans issue.

Most likely the mechanic didn't have an FSM handy and wasn't sure, but assumed it did.

Is it possible that the mechanic mis-read the code?
In my manual, I see a P1650-Quad Driver Error (Shift Solenoid Error).
Might this fit better?