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Unread 07-05-2013, 04:42 PM   #1
Beaniam
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Has anyone ever resolved "check engine light on, no codes" issues?

Have a 99 Cherokee 4.0 auto here that the check engine light keeps popping on at random. I tried plugs, wires, cap, rotor, and the tps but it still does it. Seems like every other day. There are no starting, running, or idling issues. No surging, no missing. I have scanned it with 2 different code scanners, tried the key on, push odometer button method and continues to read no codes. Also no pending or stored codes. I went as far as unplugging a spark plug wire to simulate a misfire just to see if there was something wrong with the obd2 connector but when the light popped on there was indeed a misfire code. So I just keep clearing the light each time it comes on. This is an issue now though as inspection is due this month. If the damn light is on it's not going to pass. One thing I have noticed though with either code scanner I am unable to establish a link with the engine running to pull live data... Every single thread I find through google leads to dead forum threads that were never resolved aside from one guy saying it was his evaporative purge solenoid. I'll try this also I guess... I don't know what to do next, find a new computer? I would think O2 sensors or coolant sensor would throw a related code.

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Unread 07-07-2013, 07:55 PM   #2
laybackman
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Quote:
Originally Posted by Beaniam View Post
Have a 99 Cherokee 4.0 auto here that the check engine light keeps popping on at random. I tried plugs, wires, cap, rotor, and the tps but it still does it. Seems like every other day. There are no starting, running, or idling issues. No surging, no missing. I have scanned it with 2 different code scanners, tried the key on, push odometer button method and continues to read no codes. Also no pending or stored codes. I went as far as unplugging a spark plug wire to simulate a misfire just to see if there was something wrong with the obd2 connector but when the light popped on there was indeed a misfire code. So I just keep clearing the light each time it comes on. This is an issue now though as inspection is due this month. If the damn light is on it's not going to pass. One thing I have noticed though with either code scanner I am unable to establish a link with the engine running to pull live data... Every single thread I find through google leads to dead forum threads that were never resolved aside from one guy saying it was his evaporative purge solenoid. I'll try this also I guess... I don't know what to do next, find a new computer? I would think O2 sensors or coolant sensor would throw a related code.
If the CEL lights up there is a DTC being set. Generic code readers sometimes fails to read these TDC's. Did you try Autozone? They will pull the codes for free.
Ine the meantime. One of the problems that are hard to diagnose is a small leak in the closed fuel system caused by a bad gas cap. Replace it with a cap that does not have the plastic center mounted lanyard.
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Unread 07-09-2013, 11:49 AM   #3
Beaniam
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I'll try the gas cap. One of the code readers I've tried is literally the same actron scanner they use. It never seems to come on when I'm driving it. Only when my gf is. She does mention she smells gas when the light comes on. I never smell it when driving and the light is off.
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Unread 07-09-2013, 12:13 PM   #4
laybackman
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Quote:
Originally Posted by Beaniam View Post
I'll try the gas cap. One of the code readers I've tried is literally the same actron scanner they use. It never seems to come on when I'm driving it. Only when my gf is. She does mention she smells gas when the light comes on. I never smell it when driving and the light is off.
Even though the fuel system is a 'closed' system that cap is actually vented The inside valve set up inside the plastic fuel cap has some metal parts.

I sprayed the crap out of mine with WD-40 and the problem went away for several weeks...only to come back. New cap no more CEL for a small leak detected in the fuel system. IIRC it is DTC P0442.
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Unread 07-09-2013, 04:40 PM   #5
Beaniam
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Finally tried a scanner that pulled something. p0455 evap leak. Just put a new gas cap on and have a purge solenoid on order.
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