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Old 07-16-2013, 04:29 PM   #1
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Default Check engine light

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.
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Old 07-16-2013, 06:14 PM   #2
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Did check the fuses?
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Old 07-16-2013, 10:53 PM   #3
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Default check engine light

Have check all fuses, and relays, under dash and in engine compartment.
All good.
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Old 07-16-2013, 10:59 PM   #4
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You may have a computer issue.
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Old 07-17-2013, 10:18 AM   #5
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Default Check engine light

Any way for Me to check the computer, or would I have to go to the Jeep Dealer?
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Old 07-17-2013, 11:13 AM   #6
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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.
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Old 07-23-2013, 08:20 PM   #7
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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
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Old 07-24-2013, 10:45 AM   #8
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Hi, JJCIII
Do you disconnect the negative cable from the battery, before
connecting the positive cable, to the negative cable?
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Old 07-24-2013, 10:50 AM   #9
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Quote:
Originally Posted by Joe34 View Post
Hi, JJCIII
Do you disconnect the negative cable from the battery, before
connecting the positive cable, to the negative cable?
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.
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Old 07-24-2013, 10:46 PM   #10
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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.
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Old 07-25-2013, 11:09 AM   #11
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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.
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Old 07-25-2013, 01:09 PM   #12
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Quote:
Originally Posted by Joe34 View Post
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.
But did you check for specific communication to the pcm or just the relay to the guage?
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Old 08-01-2013, 04:58 PM   #13
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Default Check engine light, now will not start

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?
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