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Ron Z.
Ron Z., - Jeep Tech -
Category: Jeep
Satisfied Customers: 18784
Experience:  18+yrs experience. State Inspector & Jeep Diagnostics/Repair
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2004 Grand Cherokee diognostic codes P0455,P1489,and P1490.

Customer Question

2004 Grand Cherokee diognostic codes P0455,P1489,and P1490. How do I repair?
Submitted: 7 years ago.
Category: Jeep
Expert:  Ron Z. replied 7 years ago.

Ok. The p0455 is more than likely due to a faulty/loose/missing gas cap. The p1489 & 1490 are pointing to the low&High speed fan relays, however it is very uncommon that these 2 relays go at the same time, and is more likely a result of a faulty Pulse Width Modulated (PWM) cooling fan relay which controls both Low&High speed relays. This PWM Fan relay has always been a major defect in Jeeps. This relay is located below the right headlamp behind the bumper fascia.


Customer: replied 7 years ago.
I replaced my fuel cap about 2 days ago. Would the fan control module be the cause of the check engine light being on? I thought that by replacing the cap my check engine light would turn off being that the code specifies a evap-system leak. How would fan relays prompt a check engine light?
Expert:  Ron Z. replied 7 years ago.
The n control module IS this PWM relay. This relay has a well-known Jeep fault. The relay is monitored by the on-board computer and when it fails it will interrupt operation of both Low & High speed relays located in the relay box under hood. As for the gas cap, the code is a evap system leak. In the diagnostic flow-chart, the first, most common is the gas cap. Jeep recommends an OEM gas cap as a replacement, as the cheapies sold at AutoZone usually don't cut the mustard. As for the light going off by itself- not with ever repair. When a fault is tripped, the code stays in memory until manually cleared. You can clear the code either with a scan-tool (recommended) or by removing the "NEG" from the battery for 5min. If you use the "NEG" method, make sure your remote for your alarm is working and you have a radio anti-theft code (if either is equipped) as these systems usually reset at the same time.
Ron Z. and 5 other Jeep Specialists are ready to help you
Customer: replied 7 years ago.
Thank You. I was pleasantly surprised by your knowledge and the information you have provided me. Now, how do I change headers on a '98 Mustang. Just kidding! Thanks again.
Expert:  Ron Z. replied 7 years ago.

hahahahaha! Headers on a Mustang?! Why bother! Junk it and buy and old GM, they make much better HotRods. If I had a nickle for every Mustang i've beaten with that green Cutlass in the pic, i'd be rich!


Glad I could. Have a great day!