I have a 2004 Sedan... CEL light is on and the auto shop told me that my oxygen sensors are bad (pre-cat). I got under the car and didn't have much luck locating the sensors. Am I looking in the wrong place? Where are the 2 pre-cat o2 sensors located? Thanks!

 

If my memory serves me right they are on the headers once it molds to the single tube. Right above the cats. I didn't think CEL lights were common for precat 02 sensors. How many miles do you have?

 

Just over 100k. I don't guess I'll be able to see them or access them if I remove the engine cover?

 

I would jack the car up and look from the bottom. You can probably see them from the top, but if you plan on replacing them from the engine bay you might run into some tight spots. Not 100% I would have to go look.

 

Did they tell you which sensor was bad? Or did they just tell yup all pf them?


Do you have or can access and obd2 scanner with live data capability? It will allow you to read the voltages of all the sensors and determine which is bad.

 

I'm really doubting it's precats.

 

if its pre cat it should be right on the exhaust manifold or pretty close to it

easier to see if you are under the car

sometimes the connector just gets dirty or the o2 sensor just needs cleaning

 

The auto shop I went to gave me a service bulletin for the codes (p1031, p1051, p1148, p1168) that they say applied to me. I'm going to pull the codes again today at lunch to see specifically which codes I have. I'll report back

I didn't realize that the sensors sometimes just need cleaning. I already bought 2... got a pretty good price on 2 oem bosch for $96 each.

 

Unless you really trust the garage I would be hesitant to replace the o2 sensor. Most times the cel light comes on it is because the gas cap was not tightened enough or needs to be replaced. Either way it is a much cheaper fix than an 02 sensor. Try tightening it, see what happens. If that doesn't fix it then buy a new gas cap and see what happens. I do not remember how many miles you have to drive continuously to reset the cel, but I believe it is 50 miles. An easier thing to do is go to an auto parts store and have them reset it using their scanner.

 

Just ran the codes and I got 1168 and 1051. Does anyone know what those codes mean or where I can look them up?

I didn't have a CEL until a couple weeks back after I had normal maintenance done for 100k service. New spark plugs, new fluids (radiator, brake, transmission, rear diff). When I went to pick the car up they noticed that my inspection was expired so they started to run the test but then noticed my CEL was on. Pulled the codes for me and told me that most likely my o2 sensors (pre-cat) were bad. They gave me a service bulletin (ITB04-027a dated August 28, 2006) which said if 1051/1068 show to
stepA
perform a/f sensor test to confirm proper air fuel operation... (if the a/f sensor fails test this bulletin does not apply).
compare current ECM part # to chart A in service bulletin and if it does not match one then the bulletin does not apply.
stepB
If this bulletin applies, reprogram the ECM.


Would it be fairly uncommon that I would need to reprogram the ECM? Obviously this isn't something that I'd be able to perform myself. Has anyone else come across this issue?

 

So you had work done to the car and the cel came on? Or was it on before?

I'd erase the codes, drive and see if it comes back first. Then start troubleshooting. I'd also clean the maf with some electronics spray cleaner as well


The gas cap usually triggers a p0455 code, so I don't think that is the cause. However, if you google search those codes together, you'll find others have had this issue and a dealer reprogram is a way to fix it. Unsure if changing the o2s would do it.

 

Yeah there was no code before I got a tuneup. I've erased the codes but they come back in less than a minute.

I was hoping to avoid the dealer Since I got the o2 sensors I'll try them. (should be a quick install) If that doesn't work then I'll put my tail between my legs and surrender to the dealer.

 

Good news... my o2 sensors aren't bad. After removing the air intake I found the o2 sensor unplugged. Hopefully just a mistake (and not another auto shop trying to pull a fast one) by the auto shop when they were installing new spark plugs. So I saved quite a bit of money... I'll return the o2 sensors for a refund.

Thanks for your help and suggestions.

 

There are 4 oxygen sensors, 2 per side before the cats and 2 per side after the cats. I would put 2 AFRs, connect to the ones before the cats. Cannot remember the colour codes for the wires, but follow the wiring and the connectors are pretty easy to get to.