Jeep Grand Cherokee Check Engine Light Issue?

Question

I own a 96 Grand Cherokee with an In-Line 6 cylinder with auto trans. The check engine light comes on as soon as I turn on the head lights. Further, although the engine is not over heating, the engine over-heat warning bulb to the extreme right of the analog temp gauge lights with the check engine light. By disconnecting / reconnecting the battery, the check engine light  resets and remain off until I turn on the head lights. If I don't turn on the head lights,  check engine light remains off. My guess is that there is a short in the electrical harness or possibly a bad instrument cluster bulb. Also I did the self diagnostics via turning the ignition switch on/off for 2 cycles the back on so to display a code. Two codes come up: 12 and 21 indicating a bad O2 sensor and the other indicating that power was lost to the PCM. But due to the behavior of when the Check Engine light being triggered by turning on head lights, I'm thinking it's a wiring issue. Thanks in advance for your help

CJ · Accepted Answer

Check engine lights can be delt with at your local auto zone. Have them do a diagnostic:)

HD · Answer

has the vehicle been in an accident or had any aftermarket elect component added that you know of? i agree with you, o2 sensor probably not, wiring issue more than likely. i doubt
if it's the harness, more like a short somewhere that would effect the pcm thus setting the code. Now, just have to figure
out in addition to the headlight switch being turned on, the short( I assume it's a short) is setting the code by effecting another elect part, like maybe the alternator somehow. i believe that has an internal regular (in the alt.). i wish you luck
on this one my friend, elect problems can be a nightmare as
you know and is why shops charge $100.00 hr. sometimes to
diagnose elect problems.  ps: at least when you reset, the light stays off so it's not a hard code, but, that would be easier to diagnose but. probably more expensive to fix.

Anonymous · Answer

I have a 99 Cherokee Sport that does the same thing. My instruments also cut out from time to time. It's been doing that for a couple of years and nothings become of it. Try putting a piece of black electrical tape over the "check engine" light. You'll never see it again.

Rich · Answer

When the computer goes, weird stuff starts happening with cars.  PCM = Primary Control Module = computer

brenda st · Answer

sounds like you got it you could chase it down by sticking a pin in the line to hook your gage to and checking for the short but on a 96 i wouldnt bother

Jeep Grand Cherokee Check Engine Light Issue?

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