P0141 & P0161 errors

[Redbarn]

I have a year 2000 Land Cruiser, 100 series with circa 198k miles.
My CEL came on about a month ago & I read P0141 & P0161 codes.
These are rear oxygen sensors heater circuit codes.
I reset the CEL & after at least 30 miles, it came on again.
So I put the truck up on the lift & replaced all 4 oxygen sensors with genuine Toyota parts.

The truck ran better (albeit subjectively) right away.
However, the CEL has started coming on again with the same P0141 & P0161 codes.
I’ve done a search through the forum & cannot find any experience of this.

Any body able to shed light on this problem ?

 

[excessive]

check wiring and fuses, make sure you got the correct O2 sensors as well

 

[YezusLX]

check wiring and fuses, make sure you got the correct O2 sensors as well

I second this. I had a rodent issue and found nicks in a lot of wiring and replaced them as they come up. Also, a good cleaning of the intake/fuel system could help in this instance and for preventative maintenance. If MAF sensor sees one thing and new O2 sensors see something else it will be quick to throw a light. Obviously, there is the throttle body, intake manifold, and combustion chamber in the way between those sensors. So any disruption down the line could cause a CEL. That being said please also double-check coil packs and plugs a misfire can make strange things occur if it does not throw a code for it. Hope this is useful for you.

 

[Redbarn]

Gents,
Thanks for your help.

What is so frustrating about this particular problem is that it only occurs on drives of over 20 miles or so.
If I drive to the Post Office or the pizza store, it doesn't occur.
So the ECU is seeing something that triggers the CEL on an irregular basis.
Even then the codes are shown as temporary codes, not permanent codes & so are easily reset.

excessive,
I'm certain I got the correct replacement oxygen sensors as they have the same parts numbers & codes as the ones that I replaced.

YesusLX,
I had not thought of the MAF sensor & the intake being involved. Very good idea !
I'll investigate changing the MAF. I had an MAF problem on a previous Range Rover & that took ages to figure out.

 

[YezusLX]

Gents,
Thanks for your help.

What is so frustrating about this particular problem is that it only occurs on drives of over 20 miles or so.
If I drive to the Post Office or the pizza store, it doesn't occur.
So the ECU is seeing something that triggers the CEL on an irregular basis.
Even then the codes are shown as temporary codes, not permanent codes & so are easily reset.

excessive,
I'm certain I got the correct replacement oxygen sensors as they have the same parts numbers & codes as the ones that I replaced.

YesusLX,
I had not thought of the MAF sensor & the intake being involved. Very good idea !
I'll investigate changing the MAF. I had an MAF problem on a previous Range Rover & that took ages to figure out.

If you are only getting this in longer drives, I would posit that the ECU needs a full cycle before clearing codes as well. If memory serves Toyotas require something like a 60-mile uninterrupted cycle for a completed relearning for ECU in regards to emissions. You may just have the CEL from previously thrown codes in the memory because it has not yet completed an entire relearn cycle. I just learned this recently on mine when I changed alternators, alternator harness (erratic voltage), and some sensors (coolant temp, Oil pressure, and rear O2s). It kept smoking and I had forgotten I had done the BG high-pressure fuel treatment (the vehicle sat for weeks waiting on other parts) and threw all kinds of smoke but never ran erratically. Once I completed somewhere around 75 miles of uninterrupted driving then resetting ECU, no smoke, no codes, and more importantly no CEL. I even got better mileage. Might be worth burning half a tank in fuel then resetting the light and seeing how things behave after.

 

[Redbarn]

If you are only getting this in longer drives, I would posit that the ECU needs a full cycle before clearing codes as well. If memory serves Toyotas require something like a 60-mile uninterrupted cycle for a completed relearning for ECU in regards to emissions. You may just have the CEL from previously thrown codes in the memory because it has not yet completed an entire relearn cycle.

YesusLX,

That makes good sense.
Is there a short cut to resetting the ECU ? Like battery disconnect ?

 

[YezusLX]

I was incorrect about 60 miles. Here is correct the reset procedure per Toyota. Just look for 2UZ-FE or Land Cruiser and this will walk you through it.

https://justsmogs.com/wp-content/uploads/2019/03/toyota-smog-check-drive-cycle-monitors.pdf

 

[YezusLX]

YesusLX,

That makes good sense.
Is there a short cut to resetting the ECU ? Like battery disconnect ?

Yeah, removing the negative terminal for around 20 minutes does a hard reset.

 

[Redbarn]

Yeah, removing the negative terminal for around 20 minutes does a hard reset.

Thanks.
I'll try that first then report back.

 

[YezusLX]

Thanks.
I'll try that first then report back.

You're welcome! Sounds like it will be a relatively simple fix soon enough.

 

[Redbarn]

To close this thread.
I cleaned the MAF with CRC Mass Airflow cleaner.
Probably not relevant to my issues but easy enough to do anyway.
I had already changed all 4 x O2 sensors.
I then left the negative battery terminal disconnected overnight (easier than knowing whether the reset time is 10 minutes or 20 minutes !).
So far the P0141 & P0161 codes have not reappeared after about 60 miles.