Well, over the course of the last few months I have systematically replaced everything that is usually listed as the common culprits for this code combination.

New 02 Sensors x2
New Catalytic Converter
New Idle Air Controller Valve (IAC)
Upgraded neon injectors

Yet I am still getting an intermittent p0138 and -p0141 combo which turns the CEL on. The CEL may be off for two weeks, then come on for 4 days, then go off again. It's rather temperamental, and that's what is unusual.

And unfortunately, getting 15 mpg every tank is just sad. I was getting 19+ when i bought it 10 months ago.

I assume, from searching, that the problem likely lies in the circuit. Before I start tracing wires though I just wanted to ask one last time for any extra input or advice on how to check the circuitry. If you have any input, please let me know. Thank you,

 

mine was doing the same thing. Mostly off than would randomly come up the code. turned out being an exhaust leak at the header flange before the o2 sensors

 

Thank you for the response! Interesting... were you getting terrible fuel mileage as well? and did you repair it or replace it?

 

15 mpg your lucky most of us on here will be lucky to see that

 

Thank you, but no. I was getting 19 to 20. Apart from the better injectors, it's completely stock, no lift or anything, with 90k miles on it so I know it can get better if I can work out this O2 sensor issue.

 

didnt notice any fuel mileage differences header flange bolt was missing so i just put new bolt on

 

Hi! I am having the exact same issue. Did you every figure out what was causing this? Was it an exhaust leak at the header flange before the o2 sensors??

Thanks in advance!

 

This thread is 12 years old and the OP hasn't been here since 2014 so you're not likely to get an answer.

Instead, start a new thread. Post your year, engine, mileage, etc, and a description of your issue. Include any steps you've taken so far, any parts you've replaced or any recent servicing (even if not related to the issue).

Both OBD codes above are related to the oxygen sensor after the CAT. I would start by checking the wiring harness to make sure it's not damaged.