dholbrook

Hello all it's my first post as I am a newish owner of an 89 pickup 2wd a/t. Truck has ran great but check engine light flashed and it was the code 52. I ran a new coax line from knock sensor to ECU, as I read how to do on the web. Now I have no CEL whatsoever even in "ON" key position. Truck starts and revs fine, everything works, but no CEL. I pulled the dash apart and bulb is good. I checked for voltage at the violet "W" wire from the ecu and there is no power in "ON" or "START". What to do/check? As far as I can tell every fuse in engine bay and driver kick panel is good. Battery, Seat belt, gear light all come on dash, just no CEL. Truck PO did a real mickey mouse job on wiring, I even think my ECU is from a '90 pickup.

I of course want my CEL to work, but I need to pass CA smog ASAP. Please help, I've been taking one step forward, three steps back for three days now.

abecedarian

CEL won't light up except when turning the key on, and it won't flash unless there is an issue. Even then it won't flash codes unless jumper is in the diag connector.
The CEL should come on when you turn the key on, but will go out. Changing the KS cable won't cause the light to not come on.

So, what are you not telling us?

dholbrook

If it matters, when I was grounding the shielded cable I accidently shorted it out because the bat was still hooked up, I got worried, but figured the ecu was fine because all other functions work. I have continuity of violet W wire from ecu to dash, and the only wire I spliced was the KNK wire. SO why wouldn't my ECU light the CEL at start up?

scope103

Ow! Checking the W wire is a few steps farther than most would get, and since you've also checked continuity it seems pretty clear that you're getting no CEL signal from the ECM. Which will flunk you for smog for sure.

My guess is that you cooked the ECM. I've never done it, but others don't seem to have too much trouble finding used replacements to swap in.

Good luck!