Dear Forum members,

I have a 2000 ES300 that gave error code P0171 (bank 1 lean) for a long time.
After replacing various parts and eventually thoroughly cleaning the engine air intake, the error code cleared and the engine ran smooth.
The next day the engine ran very rough and wanted to stall at each full stop.
Two coils were replaced and the engine ran smooth again.
The next day the Nox sensor error code came up, followed the following day by the code for the other NOx sensor ...
Both the NOx sensors were checked and their resistance are both in range.
The NOx sensor wires were replaced by new ones and all the wiring to and including the "computer" were checked/diagnosed to be in working order.
But both the Nox sensor errors are persisting ...
I very much appreciate any ideas on how to tackle this obNOxious problem, which prevents the car from passing the Californian smog test.

Thanks !

 

Lmao it's called a knock sensor.
Few things:
Bad o2 sensors can cause knock sensor codes
Same for bad spark plugs
Also did you buy OE knock sensors or the cheap ones?

Anything other than oe knock sensors will most likely throw a code

 

What are the various parts you have replaced?
Of those parts, which were not OEM?
And what are the current code numbers showing on the scan tool?

 

Dear CRWYS,

Thanks a lot for your expert feedback !

They checked the spark-plugs and the O2 sensor and found them to be ok.
They tested the knock sensors and found them to be ok.
They did replace the "harness", which I understand consists of the wiring to the knock sensors.
The knock-codes went away but we don't know why;
whether it's the new harness, or the intake cleaning aftermath, or anything else that caused them to clear.
I got it back from the garage and have driven it about 15 miles and no check-engine light yet ...

The immediate victory is that it passed the smog test; yeah !

I did forget to mention that a lot of the time the engine runs in some kind of high-RPM mode,
where it runs about 1000 RPM too high.
It used to get stuck in this high PRM mode after accelerating "normally", like from a standstill.
And would not come out of it until the engine was turned off.
It still goes in high-RPM mode often, but doesn't get stuck there.
I have no idea if this is related to the error codes that were generated.

And yes; that's indeed funny.
It sounds like "noksensor" over the phone ...
and as we're trying to pass the smog check, NOx jumped to mind ...
Reminds me of a nok-nok hoos there joke.

 

Dear Fortitude,

Thanks for your reply.

The catalytic converter was replaced, as well as the O2 sensor earlier.
I believe the catalytic converter was OEM, but I don't know about the O2 sensor.
I also don't know the scan-tool-codes that the knock sensor produced.