1990 K1500 refusing to flash out codes

[sdryluth]

Hey folks, I've got a weird one.

My new to me 1990 K1500 has a check engine light on. Sometimes it turns off for a second or two while i'm driving, but it always comes back on.

The problem is, I can't seem to get the codes out. Shorting pins A and B on the diag connector together does nothing. The Check Engine Light stays on solid the whole time whether the pins are shorted or not. I checked and Pin B has 5 volts power with key on, and Pin A has 0 ohms to ground, which I think is normal?

Any idea why it would be doing this?

 

[movietvet]

So, to be sure, you are crossing the pins on the top two right of the connector? You can supply a different ground wire if you want.

 

[Schurkey]

You must be registered for see images attach

A and B are the correct pins to jumper. You've also got the proper electrical properties on "A" and "B" according to your description.

If you don't have the flashes at the MIL with key on, engine off, I'd suspect a failed ECM, or the instrument cluster has a perpetual ground keeping current flow through that bulb socket.

 

[Schurkey]

^^^ My previous post is awaiting Moderator approval.

 

[sdryluth]

Yeah I double checked and i'm shorting the correct pins. I also tried going to another ground and no difference. It runs and drives perfectly fine so I wonder if like you said the CEL being on is some kind of failure. It doesn't blink at all with key on engine off, and the only time the light goes off while the key is on is for a second or so every now and then while driving. Maybe I will pull the cluster out and see what sort of signal i'm getting to it for the CEL.