RandyL712

I'm really hoping this doesn't require new O2 sensors, that's not a cheap fix! Just came on out of the blue while driving last week. About 50k miles, everything runs perfectly still.

Any input, suggestions?

alflash

Hello,
I think, need check Freeze Frame and Live Data.
Particularly need check MAF Sensor, Long Fuel Trim (LFT > 20 perc. ?)
My be useful these links:
https://www.clublexus.com/forums/sho...&highlight=K&N
http://www.lexusownersclub.co.uk/kno...v2&id=152&c=11 and
http://www.alflash.narod.ru/harrier.htm and
http://www.alflash.narod.ru/nz.htm
HTH,

Lexmex

Go to advanced search above and select the RX400H/330/300 forums and type in P0171, and it should give you an idea. It is perhaps the most common OBDII error you will see on the RX300.

Best advice, reset the light with the scanner or pull the negative battery cable.

RandyL712

Well pulling the battery overnight did the trick. Thanks!

alflash

Hi,
Note.
1."EPA is allowing the manufacturer to extinguish the MIL after three subsequent sequential driving cycles of similar operation (as discussed below) in which a system fault did not reoccur." And Lexus (e.g.RX300) use it Rule.
2."The OBD-II system may erase a fault code and the hours run by the engine and freeze-frame information if the same fault is not re-registered in at least 40 engine warm-up cycles".
Remove the EFI-fuse or a disconnecting negative battery cable help only for Clear Memory (erase DTC, Freeze Frame, etc.) and does all Monitor in status "INCMPL" .
But this not the Way for fix (remedial ) the Problems ...
Best Regards,

Lexmex

That is a good point alflash.

With regard to point 1, I have seen this happen as I drop in altitude from Mexico City to Laredo. P0171 error as I descend...then it goes out after a few stops, i.e., starting the car 3 consecutive times.

With regard to point 2, after my experience in point 1, I went to check to see if old code was still in memory (via OBDII scanner) and nothing

On second part of point 2, you are right if you pull EFI fuse or negative battery cable, your readiness monitors show not ready, incomplete, etc.

A lot of people in OBDII testing states make the mistake of doing above to get rid of MIL/CEL only to find their readiness monitors fail them on the test.

In my experience, I have found that good solid drive of 60 minutes straight clears this up with mostly city driving and some higher (over 55 mph) for about 15 minutes. I have a scanner from Actron that does monitor those readiness monitors, Cat, O2 sensors, etc.

BTW, even without my precats I still show my cat passing on the readiness monitor.

RandyL712

Check engine light came back on, so I just cleaned the MAF sensor. Crossing my fingers that this solves the problem, it was relatively dirty.

Lexmex

Climate can also play a role. At the track on Saturday night, several cars (including my own) popped off check engine lights at roughly the same time. I had a small Actron OBDII scanner and scanned all of the cars (post 1996+ on the ones I could scan) and it came up with P0171 errors on all cars. The humidity and air temperature were fluctuating according to the instruments we keep at the track and we had some wind.

It reminds me of when I am somewhere and all of the people, including me, yawn at the same time.