O2 sensor?

[JLamb85742]

I receintly had the transmission harness contact the exhaust pipe resulting in a shorted wire and blowing the E.E.C relay 30A fuse. This resulted in a non-starting vehicle. Once repaired the "check engine" light comes on. Dumping the codes shows an O2 sensor error (says the dealer). Vehicle runs OK but could be better. What to check? Where is the O2 sensor and how do you test it? Any thing else it could be? Something in the wiring?

 

[mitch]

welcome, and dont take this the wrong way but do a search first. this topic has been covered a lot. i dont know much about the wiring, but i can tell you that 93 and lower explorers have only one o2 sensor and it is in the one of the manifolds, i forget which one.

 

[JLamb85742]

Thanks

Thanks Mitch. I took a quick look thru the 1st few pages and didn't find anything so I posted. Later I found the search box and as you said several very good posts. I don't post much in general so this is all new and my ettiquete is lacking. Thanks again.

 

[Rhett]

I receintly had the transmission harness contact the exhaust pipe resulting in a shorted wire and blowing the E.E.C relay 30A fuse. This resulted in a non-starting vehicle. Once repaired the "check engine" light comes on. Dumping the codes shows an O2 sensor error (says the dealer). Vehicle runs OK but could be better. What to check? Where is the O2 sensor and how do you test it? Any thing else it could be? Something in the wiring?

First of all I would clear the codes by leaving the neg. terminal disconnected from the battery overnight.

The reason being, I would want to make extra sure that the code I was seeing was persistent, and not a fluke. If in fact you have an O2 sensor that is wearing out, the check engine light WILL come back on, rest assured.

If you're getting terrible mileage (below 10-11 mpg on our trucks), an O2 is a possible cause. If you have a rough idle when the engine is warmed up, an O2 is a possible cause. If you have the truck dying while driving or idling, an O2 is a possible cause.

You are lucky in that you only have 1 O2 sensor on your truck, so that means if you replace it, you'll only have to spend $40-$45 for the single sensor.

Yes the sensor can be tested after removal, and it can be done by heating the business-end of the sensor (often with a blowtorch) and monitoring the voltage it is returning with a voltmeter.

Most people just replace the sensor though. If an O2 sensor has been in there more than 100,000 miles or 8 years, it could go out at any time. It may just be a coincidence that it has gone bad on you just at the same time you had the other problem with the wire shorting out.

 

[JLamb85742]

I do have a rough idle - I attribute it to low compression in one cylinder, likely caused by an earlier head gasket failure. Gas milage is ok (~20 mpg) and it runs OK as well but it could be better. Its at about 160K miles and has never been replaced. Probably worth doing just as PM.

 

[Rhett]

I do have a rough idle - I attribute it to low compression in one cylinder, likely caused by an earlier head gasket failure. Gas milage is ok (~20 mpg) and it runs OK as well but it could be better. Its at about 160K miles and has never been replaced. Probably worth doing just as PM.

Well then I would just reset the computer, and see if the CEL comes back on in the days that follow. No point in spending $$$ if you don't have to; and O2s are a pain to replace in my opinion. If you can achieve about 20 mpg on the highway, you're doing pretty well, and your O2 is probably ok...or it has been ok. If you find mpg tailing off, and you get O2 CEL codes, then you know what to do.

I agree, with 160,000 that original O2 could go at any time. But I have seen them go longer than that.

 

[JLamb85742]

O2 sensor changed

Rhett: Thanks for the help. I reset the CEl but it came back. You are right about the O2 sensor being a PITA. Once I figured out that I needed to go thru the passenger wheel well to re-connect the harness the screaming and cursing stopped. All else went well. Driveability is improved overall. Idle roughness marginally improved. No CEL so far (~100 mi.). When I pulled the old sensor, the metal cover over the ceramic (?) sensor itself was completely gone. From the head gasket failure - i.e. excess water vapor n the exhaust? Odd. Anyway, thanks again - this really is a great site.