Check Engine Light Keeps coming on.....

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Ed Wojciechowski - 29 Jun 2004 13:20 GMT

About two weeks ago my check engine light came on. I have a '96 GC Laredo
with a 4.0 engine. I went and had Autozone check the code and it was PO138.
Got the Haynes book out and it said it was the o2 sensor before the cat. I
replaced it and drove for a few days and the light came back on, went to
Autozone and it was the same code. It's happened three times since I
replaced it. Any suggestion as to why it keeps coming back?

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John Davies - 29 Jun 2004 14:04 GMT

>About two weeks ago my check engine light came on. I have a '96 GC Laredo
>with a 4.0 engine. I went and had Autozone check the code and it was PO138.
>Got the Haynes book out and it said it was the o2 sensor before the cat. I
>replaced it and drove for a few days and the light came back on, went to
>Autozone and it was the same code. It's happened three times since I
>replaced it. Any suggestion as to why it keeps coming back?

An engine code tells you that there is a problem in that particular
circuit. It doesn't pinpoint the component itself as the cause. Since
you have pretty much eliminated the O2 sensor itself, then there is
probably a problem in the wiring or a connector. Unless you got a
sensor that is bad out of the box - unlikely but possible, I guess.

You need to inspect the wire harness under the Jeep to see if it is
damaged (burned or crushed), and maybe get out the VOM and do some
continuity tests between the ECU and the O2 sensor connector.
This might be a good one for a certified tech at the dealer.

Good luck on this one. :(

John Davies
http://home.comcast.net/~johnedavies/
'96 Lexus LX450
'00 Audi A4 1.8T quattro
Spokane WA USA

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HarryS - 29 Jun 2004 23:12 GMT

> About two weeks ago my check engine light came on. I have a '96 GC Laredo
> with a 4.0 engine. I went and had Autozone check the code and it was PO138.
> Got the Haynes book out and it said it was the o2 sensor before the cat. I
> replaced it and drove for a few days and the light came back on, went to
> Autozone and it was the same code. It's happened three times since I
> replaced it. Any suggestion as to why it keeps coming back?

Codes don't mean diddly they just provide a starting point. You need to
trouble shoot using the go-no-go part of the shop manual which could be
quite lengthy. Codes are symptomatic so all you are doing is treating the
symptoms not the problem. The only true way is to hook up the vehicle to a
computer (OBI/II) and read the data stream that is the only true way to
diagnose what your issue is.

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HarryS
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Jersey - 30 Jun 2004 00:03 GMT

> About two weeks ago my check engine light came on. I have a '96 GC Laredo
> with a 4.0 engine. I went and had Autozone check the code and it was PO138.
> Got the Haynes book out and it said it was the o2 sensor before the cat. I
> replaced it and drove for a few days and the light came back on, went to
> Autozone and it was the same code. It's happened three times since I
> replaced it. Any suggestion as to why it keeps coming back?

I've been told a gas cap going bad or loose could cause this kinda thing.

L8r - Jersey

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L.W.(=?iso-8859-1?Q?=DFill?=) Hughes III - 30 Jun 2004 00:37 GMT

That would be P0457 fault code:
http://www.wjjeeps.com/faultcodes.htm
God Bless America, ßill O|||||||O
mailto:LWHughes3rd@aol.com http://www.billhughes.com/

> I've been told a gas cap going bad or loose could cause this kinda thing.
>
> L8r - Jersey

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bllsht - 30 Jun 2004 06:22 GMT

Are you sure that's an O2 sensor code? I thought that was a muffler bearing
code. Have you replaced that yet?

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