Joe34

Have a 1999 Jeep Grand Cherokee 4.0.
Check engine light will not go off.
It came on when the cooling fan relay went out, I replaced the relay and the complete cooling fan assembly. Removed battery cables to clear light, 5min, then 10 min.then 30 min. no luck still stayed on. Thought may be it could be a defective relay, but that was not the case. It still stays on.
Traced the wire from the relay from the wiring harness to the fire wall,
to the dash gauge assembly, to the circuit board for the light bulb, for the check engine light, and with key in on position it has a hot wire to the bulb circuit.
I have a scanner and on I/M Readiness it shows MIL Off, and on Drive Cycle it shows MIL Off? The scanner shows no codes, or no stored codes?
The stupid light still stays on?
Any help. Thanks.

Bustedback

Did check the fuses?

Joe34

Have check all fuses, and relays, under dash and in engine compartment.
All good.

Bustedback

You may have a computer issue.

Joe34

Any way for Me to check the computer, or would I have to go to the Jeep Dealer?

Bustedback

There is a long troubleshooting tree to follow before condemning the PCM. A dealer or a Jeep specialist would be the best bet for proper diagnosis.

JJCIII

Only disconnecting the battery cables will most likely not shut the light off. Try disconnecting the positive cable, jump it to the negative then turn the key on then turn your headlights on for a sec then all off. Reapply the positive terminal and see if the lights off. This process discharges the capacitors in the pcm, clearing all codes and mil light as long as there is no issue. This is known as the chrysler pcm reflash, although technically its just a hard reset

Joe34

Hi, JJCIII
Do you disconnect the negative cable from the battery, before
connecting the positive cable, to the negative cable?

JJCIII

No, its not going to cause an issue since there is no longer contact with the positive terminal on the battery. You could do it if you want but thats just an extra unnecessary step.

dave1123

That should work, however you'll have to reset your radio memory, clock, and the PCM will have to relearn your driving habits. Small price to pay.

Joe34

I did take it to the Jeep dealer, and they said it was the PCM, that the new
cooling fan relay,under the right headlamp assembly was not commuicateing
with the PMC circuit, and to replace the PCM, it was defective.

JJCIII

But did you check for specific communication to the pcm or just the relay to the guage?

Joe34

Now have a problem not starting.
Engine turns over, but will not start.
Turn key to on position, and the check gauges light stays on,
fuel light stays on, and security key light stays on.
Tried the on off , on off and on off, to make sure the security systems
cleared, checked all fuses and relays under hood and dash, again,
has full tank of gas.
Could the PCM finely died?