2001 QX4 Cat/O2 question

[Greenporter]

2001 QX4

Failed with codes p0420 and p0160
Shop told me they were going to replace O2 sensor (p0160) then upgrade ECM (can a non Nissan/Infiniti mechanic do this?) and see if the P0420 (failed Cat) went away.

I am a little confused - from what I understand the P0160 is a bad downstream sensor on BANK 2
and code p0420 is a bad CAT on BANK 1. If I am correct, and these two codes are on seperate banks, than how would replacing the 02 sensor on one bank remedy the CAT reading on the other?

Thanks for the help.
Mike

[ARKQX33V6]

P0160 Rear O2 sensor Bank 2, Circuit High voltage
P0420 TW (Two-Way) Catalyst System, Bank 1
Good question on your part. First before spending time and money try resetting your ECM, by erasing but keep a record of your codes. Then drive and wait and see what transpires.

A bad O2 sensor will return a code, but you must get this code more than once to be sure. And a high voltage reading not a retarded reading, wait and see.

The same thing with the cat.

You do not indicate the mileage on the vehicle or any other symptom. And any competent mechanic can change out an ECU, but why would you start by doing that?

ECU components are not cheap but you should verify not only the controller but the thing(s) the controller monitors, and /or the cabling. It requires the mechanic to know what he is doing and checking these things other than the black box itself is time consuming. Maybe he is too lazy to test the complete system...maybe

Your mechanic seems to be working backwards, its like blaming the messenger for the message.

[Greenporter]

he is not replacing the ECU - he is just updating the firmware after he replaces the O2. Can an independent mechanic (not Nissan) update the firmware? Not sure how I can tell if he simply cleared the codes or actually updates the firmware.

[ARKQX33V6]

OK thanks for clearing that up, I can not answer your question but it makes a good question, do you have trust in this mechanic and is he that much cheaper than Nissan?
Ask him, "How do I know that you have truly updated? His reaction might be very telling.

Good luck!

[asnorton44]

Yeah I was under the impression you had to have a Consult-II to update it?

[Greenporter]

Just spoke with him. He did not update the firmware.
He replaced the O2 and cleared codes. It passed inspection after this - the po420 did not come back.
Would not surprise me if the code reappeared soon but for now it has passed inspection.

[asnorton44]

Well I think the update helps your sensors last longer so you shouldn't see a CEL soon without it done anyways.

I had a P0158 code (bank 2 sensor 2) and it was on for a week then turned off so I guess Ill wait to see if it comes back on.