i'm doing the brakes on a friends Cavalier the other day, and notice his SES light is on when i'm finishing up.

so i grab my scan tool to check it, but it won't link to the ECM.

there is power in the port (when hooked up, my scan tool turns on automatically when the ignition key is turned on), but for some reason, it just won't link. and yes the tool is working fine, i checked it on my truck, just to be sure.

i've checked every fuse in the car & under the hood (just so no one could say, "did you check this one........?"

the only thing i can think of, is he has an aftermarket deck in the car (not sure how long, but it's definately NOT new), maybe he buggered a wire for the port somehow? (hey, don't ask me, i never installed the radio)

anyone know of what wire to check, or does someone have a wiring diagram for this car (no options at all, 2.2L/manual trans)?

 

The CIG fuse powers the DLC. Pin 16 should be the power wire so you can test it with a multimeter or test light. It would also be worth while to check for good grounds at the DLC as well.

Here is the schematic for the DLC:

 

It wont help you, but Ive encountered this on a 91 sunbird - where the scan tool wouldnt connect. I was curious so I swapped in a used computer and ran the car till the codes came back, and I was able to connect the tool to it properly. That car turned out to have a bad computer cause I went back and forth again to test it out and the used one worked everytime...

 

@ Kyle: thanks for the schematic on the DLC. i had checked the CIG fuse first thing, then all of the fuses (just to cover my butt). which is why i wanted the schematic, to make sure nothing under the dash has been hacked, or spliced, or Lord knows what.

@ ohso: it had a bad ECM, but still was able run?