her99rx300

My CEL came on a couple weeks ago and thanks to this forum I went about systematically trying to resolve it. I have a '99 RX 300 with 60k miles on it. It drives perfectly smoothly and gets about the same mileage. No black smoke from the exhausts. So far this is what I've done:

1) checked code at Autozone and it said "p0171" lean fuel bank 1
2) replaced air filter
3) cleaned MAF with CRC electronic cleaner
4) checked to make sure no leaks around intake hoses
5) double checked air filter housing to make sure no leaks
6) pulled negative cable on battery and EFI fuse

But the CEL still comes on after an hour. Even after going through steps 2-6 twice. So today I had it serviced at Lexus today for the 60k mile service and to evaluate problem. They replaced the gas cap gasket and all the usual 60k items and said the MAF sensor has to be replaced for $357 !!!

How do they know it's the MAF and not the O2 sensors? I sourced the MAF at irontoad.com for $116 which sure beats $357. I'd hate to buy a new MAF only to find that wasn't the prolem and have to replace the O2 sensors also. Do I just have to bite the bullet and buy a MAF first and if that doesn't resolve the CEL start buying O2 sensors?

Thanks for any help

TunedRX300

Ask the dealer to replace A/F sensor under California Emission Control Wararanty, which is 7 years 70K miles. See if the CEL code goes away. Also there are two sensors in MAF, one detects flow, the other temperature. Did you clean both?

her99rx300

Thanks for your reply. Is the A/F sensor the same as the O2 sensor sensor? The CA Emission warranty sounds like a good point to bring up with the dealer.

With regards to cleaning the MAF sensor I just unscrewed the 2 screws that attach it to the intake tube and cleaned the dark red diode looking part and the 2 pronged silver parts that attach the diode to the housing with a Qtip and CRC cleaner. You'll have to excuse my ignorance on this but is there another part that I should be cleaning on the MAF?

TunedRX300

Check out this photo DIY on MAF cleaning. I think you forget to clean the one in the tube, I believe that is the one that detects air flow.
http://www.lexusownersclub.co.uk/kno...v2&id=152&c=11
Bring your Lexus Owner's Manual Supplement, on the California Emission Warranty section, it says oxygen sensor is covered.
I would clean the MAF again, if CEL code still on, ask dealer to replace sensor under warranty.
People use O2 and A/F sensors interchangeably, if you really interested on the difference here is a good document.
http://www.autoshop101.com/forms/h37.pdf

Tammy

The Air Fuel Ratio sensor is California warrantied for 7 years or 70,000 miles from the original in service date. The Lexus coverage is 4 years or 50,000 miles.

This inquiry is regarding a 1999 RX.

her99rx300

You're right, I just cleaned the red diode part and didn't even see the 2 wires down the tube. Thank you for pointing out the link. One of the wires was actually black. When I used the CRC cleaner and sprayed the wires with the long thin red tube attached to the can it blew all the black soot off it leaving it shiny. I was shocked at how much junk accumulated on it. Your web link points out it should be cleaned every 2 years and that's is indeed a good point. Mine hadn't been cleaned in almost 7 years! No wonder it couldn't read properly. I'll try it out tomorrow and let you know how it goes.

Thanks again.

TunedRX300

Did the CEL code go away? How long have you used the OEM paper filter?

her99rx300

The car was only driven 30 today and so far and no CEL. I'm still crossing my fingers. The air filter was last replaced at the 30k mile service and it was pretty gray when I changed it out last week before the 60k service. I really have to praise Lexus for making it so simple to change out the air filter with no tools needed. I've never before had a car that made it so easy to do that in under 30 seconds. I'll give it another run tomorrow and see if the CEL comes on.

TunedRX300

Good luck, it seems that MAF was not able to measure air flow accurately due to clogging, causing ECM to map incorrect A/F ratio. Most likely it is not the A/F sensor's problem if the CEL stays away.

asadchinoy

The same code came up on my mom's RX300 today. I am going to try and clean the MAF and I will keep you all posted. Thanks for the help.

-Asad Chinoy

her99rx300

CEL officially gone. After 3 days and a few hours of driving no CEL.
Thanks for your help TunedRX300

TunedRX300

her99rx300,
You are welcome, I am glad you save some serious $. I suggest the next preventative maintenace is to drain and fill the transmission fluid.
Asad,
How long since you last changed your air filter? Did the CEL go away with MAF cleaning?

anulex

I had my CEL go away for a while then it came back and then i need two sensors. $412 each. Thank Good i had extended warranty.

TunedRX300

You earlier post indicated that Lexus replaced your MAF twice, it is good that you don't have a spend any $ to get a set of new sensors. But it is unlikely two MAFs failed in row, along with A/F sensors, seems to me the dealer used the shot gun blast approach and replace every sensor know to them. Someone posted warranty repairs are profit to dealers, no matter who pays, customers or Toyota corporate.