95 cavalier, QDM Circuit problems.

[kyanox]

Hi and greetings, i'm new to this forum so i will keep my question brief.

I have done a lot of searching the last 3 days on the net, and to no avail. Heres the symptoms of my problem.

I start the car, and give it about 20 - 60 seconds to warm up, then the CEL comes on. So i pull the codes with an AutoXray Code Reader, and it pulls code 27 QDM 1 fault - Fault B - and 28 QDM 2 fault - Fault C -. And yet it doesnt tell me what the QDM circuits drive, only that they are failed.

This wouldnt be so bad, if my Cooling fan didnt kick on, stay on, my alternator voltage didnt drop to 12.5, my turn signals stay on etc..... Basically when the CEL kicks on, the car goes into limp mode.

My question is, can someone give me a general direction to test the circuit that the QDM's failed on. I have a general idea how a QDM works, that it controls 4 12v sources from a 5v source on the PCM. I also know that if the ECU detects improper output voltage on one of the circuits, that it returns the error code.

What i need to know to complete this repair, is what circuits to test. I'm assuming the Fault B refers to a fault list, and item B is what failed on QDM 1.

If this helps, my relays pulled between 75ohm - 81 ohm, and all fuses check out as working. All terminals are corrosion free.

With the engine stopped, but ign turned all the way to run mode i did get a wierd reading, 11.5v at the PCM fuse, 12.5 at the battery??? Any reason for a 1v voltage drop in between the fuse box and the battery?

Can someone lead me in the right direction, other than the service department at the local chevy dealer. Ours has a habit of breaking more things than they fix, and then refusing to repair them.

Chris R. Smyth

[unbe]

Do you have a diagram for your car I think there are more than just relays that you should be ohming out i.e. solnoids etc

[kyanox]

Originally Posted by unbe

Do you have a diagram for your car I think there are more than just relays that you should be ohming out i.e. solnoids etc

I went to the dealer, and talked a friend into letting me look at the SECRET MANUAL. It has a procedure to use a Tech 1 unit to test 6 different systems. Prob is, i dont have a tech 1, but i do have access to a different tool which can do the same thing.

The magic book said, either EGR, AC, Cruse control, or EVAP. So that narrow's it down.

Chris

[89Sunbird]

If you go to Autozone, they have a code book for those things that have a list of what could be causing the problem...