So I just finished replacing the rear O2, because I had been getting a constant CEL (pulled p0037). Well replacing took all of 20 minutes, BUT I buttoned everything back up and I'm still getting a CEL! I tried doing an NVRAM reset, but nothing. I just went to the garage and unhooked the battery to try that way.

Shouldn't the ECM immediately pickup the new sensor and shutoff the CEL? Or am I wrong?

 

P0037 is actually for a fault on the rear O² sensor heater circuit.

Since this only works at start-up, it may just take a couple of cold starts to reset.

If it stays, it is unlikely that it is a power problem, since most of the sensors share the same fuse and supply - I would look for damage to the rear sensor's harness.

 

Are the front and rear O2 sensors different or the same? How can you tell which one needs replacing? I've seen prices for an O2 sensor ranging from $25 up to $500 how come, any answers please?

 

The sensors are different because they perform different functions.
Verify that your harness is not damaged.

 

UPDATE: So after hooking the battery back up, light was of course off. Drove for about 42 miles and no CEL. Figured if it was going to detect a problem, it would have done it within the first 20-25 miles after reset. Hopefully were good to go now!

And yes the downstream sensors are significantly cheaper than the upstream sensors. Downstream usually run $80-130, whereas upstream usually run $260-380.

 

Thanks to Charles Hill for his answer, could you now explain what those different duties are that each sensor performs please? Also to 04MicaSpd thanks for explaining the price differences. I had a new clutch fitted to my Rex last weekend and that is when the engine management light came on the following day, so could they have disconnected the sensor or damaged one of the leads, as you say to check the harness to each sensor. If the harnesses look OK, how can it be determined which sensor is at fault, will the diagnostic meter indicate which one by a different code and if so, what are these codes, anyone know? Thanks to all Club members for your help and advice.

 

Examine the front oxygen sensor harness as it is common for it to get pinched and damaged during transmission installation.

The front sensor reports the A/F ratios to the PCM, while the rear only monitors the catalyst performance.

 

The front O2 sensor is a major PITA to swap as well.

 

I've been told that the rear o2 sensor can be unplugged, and while a CEL will still occur, the car will continue to operate 'normally'. can anyone verify this?

 

^..................yes.
Some people don't even get a CEL when doing this, but most of the time it will generate one.
Sometimes it doesn't show up for awhile and then it eventually does.
Only way to really mask this CEL is with an Accessport.

 

cool! thank you!

 

I have replaced the front o2 sensor and had the EM light reset but on starting the next day the light was back on again, any ideas why?

 

Sure you replaced the right thing ?

 

the catalyst o2 sensor is the downstream sensor?
looked at ebay the only one listed is a Walker # 250-24131, has anyone used this brand?
the price is 95.

please LMEO
thanks
Jose P

 

Well once again, why is this being posted in General Discussion rather than The Tech Garage forum?


These areas are divided into specific subject groups for a reason. The most knowledgable and experienced members are not likely looking in here to provide technical experience, which not only creates numerous Search function nightmares, also likely means shooting yourself in the foot rather than receiving the best possible help in resolving your problem.