Question about OBD1 trouble codes
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Junior Member
Joined: Oct 2018
Posts: 80
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Year: 1992
Model: Cherokee (XJ)
Engine: 4.0
Question about OBD1 trouble codes
Hey all. I have a 92 Laredo. I have a question about how the trouble codes work. My check engine light is NOT on, but when I do the key trick to show stored codes, I get 12, 21, 15, 13, and 52. Are these just old codes, and if so how do I clear them? Just think it’s strange that I have stored codes but no check engine light on
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Joined: Nov 2018
Posts: 158
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From: Burleson, Texas
Year: 1993
Model: Cherokee (XJ)
Engine: 4.0L
More than likely old codes. To clear them the easiest way is to pull the negative battery cable for a bit. You will always have 12, that just says the battery was disconnected. And your last number should be 55 saying end of codes.
Thread Starter
Junior Member
Joined: Oct 2018
Posts: 80
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Year: 1992
Model: Cherokee (XJ)
Engine: 4.0
Cool, thanks. Yeah it had the 55 for end of codes too. I’m trying to track down bad gas mileage and the fact that rich mixture code and O2 sensor code were in there worried me. The O2 sensor was replaced not that long ago so that that might be why the code was in there, but still bad gas mileage
Thread Starter
Junior Member
Joined: Oct 2018
Posts: 80
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Year: 1992
Model: Cherokee (XJ)
Engine: 4.0
Okay, so I was able to clear the codes by removing the battery terminal. I just checked the codes again and all of them are gone except 12 and 21. So that makes me think that 21(check O2 sensor) came back after clearing it, even though the check engine light came on. The O2 sensor is pretty new, but maybe a bad part. I guess I’ll have to test it
CF Veteran
Joined: Oct 2018
Posts: 1,096
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From: Hunt County Texas
Year: 1995
Model: Cherokee (XJ)
Engine: 4.0L
What brand was the O2 sensor? 12 will eventually go away after a certain amount of key on off cycles. I forget what it is like 50 or something like that.
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Junior Member
Joined: Oct 2018
Posts: 80
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Year: 1992
Model: Cherokee (XJ)
Engine: 4.0
It’s a Bosch sensor, that’s why I’d be surprised if it was bad. Im thinking I have an exhaust manifold leak which is really causing the problem, engine bay smells of exhaust
Senior Member
Joined: Nov 2010
Posts: 682
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From: Good 'ol WI
Year: 1987
Model: Cherokee
Engine: 4.0
Can you hear a manifold leak? It would be a good idea to fix it anyway, if it IS leaking, mine was leaking on the fuel line, heating it up. Do the 92's have an adjustable throttle position sensor? You might put a vacuum gauge on it to see what you're getting and compare it to normal readings. A low vacuum also be a contributor. This could be caused by a hidden vacuum leak. Something to look into. Check for gummed up throttle plate and bore. It would be nice if you could get a reading off the O2. In case it was faulty from new, or gummed up by oil. Also good to check the temp sensors. Had one in my pickup that was faulty and it ran ok "most" of the time, but it would often run rich too. The ECU thought it was a different temp outside than it actually was making thefuel ratio wrong ..sometimes..
Are you running large tires?
Are you running large tires?
Last edited by Jeepwalker; Jan 13, 2019 at 10:28 AM.
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Thread Starter
Junior Member
Joined: Oct 2018
Posts: 80
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Year: 1992
Model: Cherokee (XJ)
Engine: 4.0
I haven't found any leaks yet, but I'm pretty certain there is one. strong odor of exhaust from the engine and it's loud up front. The 92's do not have an adjustable TPS, but I just recently replaced it. I think I'm going to pull the throttle body today and clean it and the IAC. I just replaced the coolant temp sensor and I removed the intake air temp sensor and cleaned it with carb cleaner. Tires are standard size
CF Veteran
Joined: Nov 2010
Posts: 5,841
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From: In the middle of Minnesota!
Year: 1999
Model: Cherokee
Engine: 4.0
2. Some HO 4.0 engines (91-01) have trouble with Bosch oxygen sensors. Not all to be sure, but there are a number of threads of engines that don't like em. I always recommend using NTK oxygen sensors for the 91-01. NTK is the OEM brand in 91-01 XJ 4.0 engines. They are inexpensive and widely available. So if you do end up replacing it, use NTK...not Bosch.
Thread Starter
Junior Member
Joined: Oct 2018
Posts: 80
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Year: 1992
Model: Cherokee (XJ)
Engine: 4.0
Well I found (at least one) exhaust leak here at the collector. I’ll order a new manifold soon. Looking at this ultra power one on rockauto https://www.rockauto.com/en/catalog/...+manifold,5860
I think I’ll pick up an NTK O2 sensor as well, just to be safe
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