I just got back from AutoZone where they pulled a code (P0138) indicating a bad rear O2 sensor. They do not carry the part. Is this a dealer part? Is it difficult to replace? Are any special tools required to do the job? The car is a 2000 GLE. Is there a code reference somewhere on the web?

 

This is a pretty common problem. A malfunction is detected when the maximum voltage from the sensor is not reached to the specified voltage- This can be caused by a number of factors- don't assume replacing the $170 part will fix the problem. They are as easy to unscrew as a spark plug; be it sometimes hard to reach...thanks Nissan...and the wire just clicks into a harness but on such a new car it may not be bad. (Afermarket 02 often do not fit the stock harness without splicing)

Possible Causes


Harness or connectors (The sensor circuit is open or shorted.)
~There is an entire troubleshooting protocol for this problem- the P code alone is not god, in other words it only suggests a problem but like a runny nose it could be an allergy, cold, flu etc...it is important to properly diagnose it before medicating it.

Heated oxygen sensor 2 (rear)

Fuel pressure or if you have recently used certain brands of "pour in tank" fuel injection cleaner, such as those containing Kerosene this can temp. trip a CEL- usually code P0135 (Sensor 1 Bank 1; FYI Bank 1 is the firewall side near #1 Cylinder) Sensor 1 is upstream or pre-cat.

Injectors

Intake air leaks

The heated oxygen sensor 2 (rear), is after three way catalyst (Manifold), monitors the oxygen level in the exhaust gas on each bank.

Even if switching characteristics of the heated oxygen sensor 1 (front) are shifted, the air fuel ratio is controlled to stoichiometric, by the signal from the heated oxygen sensor 2 (rear).

This sensor is made of ceramic zirconia. The zirconia generates voltage from approximately 1 V in richer conditions to 0 V in leaner conditions.

Under normal conditions the heated oxygen sensor 2 (rear) is not used for engine control operation.

***Note if you do replace it yourself, have Autozone reset the ECU for free (which must be done to clear the code- even if the light is off)...make sure, you clean the threads where it screws in- they make a tool for it, and use anti-seize on the threads.

Hope this helped. Many people share this annoying problem...

 

I re-seated the connector and reset the ECU to clear the code. So far, so good. I drove around for a couple of hours yesterday doing errands and the error has not reoccured. Thank you for your input.

 

Anytime- but rest assured, it will come back to life after about 10 key cycles. The SES light is just a pain in the butt with these cars- if it's under warranty have the dealer REFLASH it- there is a TSB out there on it...they will actually download all new info. into the ECU. Only the stealership has this updated software- it's about the only thing I would let the stealership do for me- that and the trans flush and fuel system cleaning., never trust the high school kids at the jiffy places. I'm interested to see how you make out- you can always email me if you have any specific questions...dave21@optonline.net...good luck- hopefully it stays off, but......... (;