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Old 08-09-2013, 03:56 PM
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CE light code says O2 sensor - dealer says coils?

Prelim info - 2008 Grand Cherokee Laredo no mods at all. Just shy of 80K on it.

CE light came on en route to (non-Jeep) dealer for an oil change (still using the coupons I got from when I purchased it). They read the code and said it was for O2 sensor, and said that is commonly due to bad coils. Now, I am by no means a mechanic but I thought the coils were part of the ignition system while the O2 sensors are part of the exhaust. I don't follow how the code for one could be caused by the other. After reading a few threads here it seems that coils going bad is not overly common. So, I am inquiring of the experts here to get your opinions.

I have an appointment set up for Monday first thing with my trusted mechanic (independent repair shop - no manufacturer affiliation/loyalty) but I will need to drive it until then. Do I run any major risk of damage given the information provided?

Much obliged for any advice/info provided!
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Old 08-09-2013, 08:26 PM
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Originally Posted by TheLoneWolf View Post
Prelim info - 2008 Grand Cherokee Laredo no mods at all. Just shy of 80K on it.

CE light came on en route to (non-Jeep) dealer for an oil change (still using the coupons I got from when I purchased it). They read the code and said it was for O2 sensor, and said that is commonly due to bad coils. Now, I am by no means a mechanic but I thought the coils were part of the ignition system while the O2 sensors are part of the exhaust. I don't follow how the code for one could be caused by the other. After reading a few threads here it seems that coils going bad is not overly common. So, I am inquiring of the experts here to get your opinions.

I have an appointment set up for Monday first thing with my trusted mechanic (independent repair shop - no manufacturer affiliation/loyalty) but I will need to drive it until then. Do I run any major risk of damage given the information provided?

Much obliged for any advice/info provided!
As long as the ce light is not flashing, you should be ok driving it there.

The coils certainly wouldn't be my first suspicion for an O2 code...the sensors themselves are a far more likely source.

I believe jeepgcoman has written up an excellent description of how the O2 sensors should work, and what they look like when they are on their way out. If you search the forums you'll find it.
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Old 08-10-2013, 01:47 AM
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Re: CE light code says O2 sensor - dealer says coils?

The thing is that, yes, they are 2 separate systems, but they both feed back to the same mothership. If there is a coil inducing a voltage spike that is making its way back to the pcm, NOTHING is impossible. Typically this causes a "dieout" concern. But I would not rule it out 100%

Having said that... I have personally not actually heard of this repair they speak of before... well coils failing I have, but not causing an O2 sensor code. Especially if it was just the express lane and they didnt actually "diagnose" it they just insta-diagnosed coils as the culprit, I wouldn't put much money on it actually fixing the problem. O2 sensors fail by themselves without coils' help.

There might be a starcase for the specific code you had and they just went off the starcase... its not one I have seen or heard of but honestly its the only logical thing that would explain the quick condemnation of coils for an O2 sensor fault.
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Old 08-11-2013, 04:15 PM
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Re: CE light code says O2 sensor - dealer says coils?

Thanks for the information. Oddly enough the CE light finally turned off today on my way to work. I am going to go to my trusted mechanic tomorrow for them to take a look see. This is my only ride so I cannot afford it to be down at all, let alone for a brief time to do repairs. This is the first I am bringing my WK to them but that is mainly because I haven't needed to. They have worked on my previously owned vehicles and have been very fair and reliable.

Hopefully I will know more tomorrow. There are a couple miscellaneous issues needing fixing so might as well check it all out at once.
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Old 08-12-2013, 05:04 AM
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Re: CE light code says O2 sensor - dealer says coils?

depends on the exact code. Have your mechanic see if there is a code stored, and if so get the exact P-code.

I imagine that a partially failed coil can cause incomplete combustion which can cause an O2 sensor to give screwy readings (and eventually foul the sensor, and eventually foul the cat) ..

The misfire detection may not be sensitive enough to detect a lousy fire, so you may not get the flashing MIL.

I've never seen it, but I could believe it might be true.
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