Engine light on AGAIN!!!

Hi everyone and happy holidays!

I recently had an engine light go on in earlier this month, and had the problem diagnosed as 4 faulty O2 sensors on the exhaust. I had them replaced and now 450 miles later it is on again. I spent some serious coin trying to find the problem the first time and now after it passed NYS inspection the light is on again. The vehicle is running perfectly fine. This morning when I started it up I smelled something strange, not the rotten egg smell normally associated with bad cats but a little different. Almost like a smoky, burning odor of some sort, all I know is that it wasn't normal, and the light went on soon after and the smell went away. I drove it around town and on a 40 minute highway round trip and the vehicle is actually running great. Mileage just turned 130k. I've heard this might be related to bad fuel, but I doubt that since I am having no drivability issues. Any and all input would be appreciated.

Chuck

just a simple thing to check for: a loose gas cap or one that isn't sealing will trip the check engine light on in some vehicles. It did it with the 97 Grand Cherokee I had. That also means if you have any leaks in the fuel system that might trigger the light as well. There must be a pressure sensor in the fuel system that looks for that so there is a possibility that it is bad in that case and there is no fuel leaks. Getting in to that all too far. Just check the gas cap.

In order for us to help we really need to know what code set of the CEL. If you don't have the means to pull the code then go to your nearest Auto Zone and they will pull them for free. Start there.

-river

Thanks for the input, I will get to auto zone to check that out. Not sure about the gas cap thing, although I have heard that happens sometimes, I went over 400 miles and one full tank. Funny though, the last time this happened it was right after a new tank of gas...hmmmm We'll see..Many thanx once again.

If the code comes up as O2 sensor again, have a look under and check if the front O2 sensor wiring was properly tied out of the way. It's possible it may be loose and melted on the exhaust.

One thing I should mention, the O2 sensors replaced were the four on the exhuast, before and after the cats. So I think this is related to that work, but if the vehicle passed NY emissions 10 days ago, I am baffled to think that this would be the same problem. I was told that if the cat efficiency is bad the light will go on.
I am afraid to take it back to the same place for fear they will tell me it is my cats that are bad.
I know I need to get the code somehow..I appreciate all the input I get here. Thanks again.

Chux01Cherokee said:

One thing I should mention, the O2 sensors replaced were the four on the exhuast, before and after the cats.

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Effectively, the entire lot for CARB-spec vehicles, which New York subscribes to along with four other states - California being one of them (the instigator, really).

So I think this is related to that work, but if the vehicle passed NY emissions 10 days ago, I am baffled to think that this would be the same problem. I was told that if the cat efficiency is bad the light will go on.

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Maybe. There is no cat-specific sensor in any XJ, though a bad sensor before or after a given cat could cause problems. While it's possible that a cat is blown, that doesn't necessarily mean that the problem's not sensor-related. What were the numbers on the emissions pass that you got?

I am afraid to take it back to the same place for fear they will tell me it is my cats that are bad.

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Let's see the pass numbers first; that might give some idea as to whether or not there's a cat problem. Definitely hit up Autozone and have the codes pulled. While I'm not a huge fan of diagnosis by OBD, in this case it seems like a good idea to at least know what it's complaining about.

Given that you're running OK and recently replaced the oxygen sensors, though, my gut feeling is that this may be a fuel evaporative (which could mean fuel cap) or return issue.

Hello again,

I went to AutoZone today and they gave me a (PO455) code which means that I have an large evaporative leak, I have it scheduled for a smoke test in the morning to find the leak...I'm really hoping it's the gas cap and not some other issue with the fuel system. I'll keep you guys posted.

one more thing

Casm,

LOVE the pic from Real Genius........I almost forgot to mention that I was told the light and the system will reset itself if the leak is sealed (say with a new tank of gas) Is that true? I religiously click the cap three times every time I get gas. This is the second factory cap that this vehicle has had. Are they susceptible to cracking? Is there any possiblity that the problem is in the filler neck or any fuel line?
Thanks!!!!

I have tracked down both the large leak and the small leak on my 2001 and on a Grand Cherokee. Neither of them involved the gas cap. It's those damn rubber hoses that DC used to connect the metal gas lines together. I did a write up on this from my 01 where I detailed all the sections of hose that were fawked. I wouldn't bother with the smoke test. It's just a matter of looking at all the rubber hoses very carefully. They dry rot. I replaced all of them on the 01. All told you're talking about 8 3 inch sections of rubber fuel line hose. If you need to know where to look for those bad sections lemme know...I bet I know right there at.

I do not know if anyone has had this problem before, but on my 90 it has a timer under the dash, and at 83,000 miles it will turn a light on the dash.This light is suppose to tell you to change the 02 sensors. The timer will not reset you have to replace it. I believe it is the emission light that comes on. Also the manual says you can unplug it, and the light will go out. Sounds like he has a different problem, I just thought that was some good info to put out. I read about it yesterday after finding someone had placed black tape over the light on mine.

Hey everyone,

Got the results back from the test, it needs a purge solenoid and a hose connector....lets hope its on the money. Its not the gas cap, oh well, looks like I gotta spend more $$$$. Any thoughts?

i agree with checking the hoses. the purge solenoid useally isn't a problem. we have replaced alot of rubber hoses, and it's not uncommon to see a cracked charcoal canister to cause the same code.

Re: one more thing

Chux01Cherokee said:

LOVE the pic from Real Genius........

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Thanks

I almost forgot to mention that I was told the light and the system will reset itself if the leak is sealed (say with a new tank of gas) Is that true?

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It can be, depending on the type of leak. If it's a gas cap leak, the gasket on the cap may be shot (or the cap itself cracked), meaning it never seals properly, thus throwing the code. However:

I religiously click the cap three times every time I get gas. This is the second factory cap that this vehicle has had. Are they susceptible to cracking?

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I've never had one crack - but, then again, on both of my XJs I've replaced the five-years-old-when-I-bought-it non-locking cap with a locking one, so at least in my case I probably haven't had them on there long enough for them to deteriorate.

Is there any possiblity that the problem is in the filler neck or any fuel line?

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Maybe, but if it were the filler neck you may have a noticeable smell of gasoline in the cabin. The filler cap was an easy check, but it sounds like you've been pointed in the right direction

I've actually had the filler neck, where it mates with the gas tank; fail from the beginning. The clue was the faint gas smell towards the back of the vehicle.

It was a bitch to track down, and the dealers fix was to throw new parts at the fuel system (under warranty). It wasn't until I mentioned the faint smell of gas, that the dealer decided to drop the tank, and the leak in the filler neck was discovered....

Hey everyone,

Got the purge solenoid replaced, along with the leak detection pump, and the lower front hose connector and all is well, good news considering I put about 200+ miles on it including some real tough hill climbs with 3 passengers and their hiking gear yesterday. Looks like the mpg has gone up a little too (always good news) Thanks for all the input.

Chuck