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Any Suggestions For Solving Check Engine Light Codes Po171 & Po446

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Hello everyone.

I just purchased my father's '99 RX300 and on the way home (250 mile trip) the check engine light came on. I took it to Autozone to have it scanned and it came up with two codes:

PO446

aaEVAP system vent control circuit

Probable cause

aa1-Open or short circuit condition

aa2-Poor electrical connection

aa3-Faulty vent control selenoid.

The other code is PO171

aaSystem too lean- bank 1 (Cylinder number 1 denotes bank 1)

Probable cause

aa1-Lean Air/Fuel ratio-fuel injector or vacuum leak

aa2-MAF sensor concern

aa3-ECI sensor fault

aa4-Faulty HO2S (heated oxygen sensor)

Now a little background. Original owner now 70 years old. Car has 52K miles mostly city and has probably only seen passing gear a dozen times in it's life and probably never over 60 mph. Always fueled with regular octane, ECT always in normal position. Never a single issue or repair outside normal tires, brakes and routine service. So that's how it was driven all it's life.

Now I get in it and drive it like I stole it all the way home in ECT Power, in passing gear almost as much as it wasn't, held 85 mph for several miles and made the 250 mile trip in 3 1/2 hours including stopping to let the dog out for 15-20 minutes, all in holiday traffic. Just to give you an idea of how I drove it as opposed to what it had been used to. Not at all advocating my driving style. It was actually when I stopped to walk the dog that I noticed the light stayed on when I got back on the road again. So my question is where do I start first? My gut tells me I blew 10 years of carbon build up out the exhaust and affected the O2 sensor but I've been doing some reading here and understand there are 2? and that it's not uncommon to have MAF issues with these. Oh, and I managed to keep a 21 mpg average as opposed to my fathers 23 hwy. Any suggestions (besides the obvious "slow down") would be much appreciated.

Thank you all in advance.

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Hello everyone.

I just purchased my father's '99 RX300 and on the way home (250 mile trip) the check engine light came on. I took it to Autozone to have it scanned and it came up with two codes:

PO446

aaEVAP system vent control circuit

Probable cause

aa1-Open or short circuit condition

aa2-Poor electrical connection

aa3-Faulty vent control selenoid.

The other code is PO171

aaSystem too lean- bank 1 (Cylinder number 1 denotes bank 1)

Probable cause

aa1-Lean Air/Fuel ratio-fuel injector or vacuum leak

aa2-MAF sensor concern

aa3-ECI sensor fault

aa4-Faulty HO2S (heated oxygen sensor)

Now a little background. Original owner now 70 years old. Car has 52K miles mostly city and has probably only seen passing gear a dozen times in it's life and probably never over 60 mph. Always fueled with regular octane, ECT always in normal position. Never a single issue or repair outside normal tires, brakes and routine service. So that's how it was driven all it's life.

Now I get in it and drive it like I stole it all the way home in ECT Power, in passing gear almost as much as it wasn't, held 85 mph for several miles and made the 250 mile trip in 3 1/2 hours including stopping to let the dog out for 15-20 minutes, all in holiday traffic. Just to give you an idea of how I drove it as opposed to what it had been used to. Not at all advocating my driving style. It was actually when I stopped to walk the dog that I noticed the light stayed on when I got back on the road again. So my question is where do I start first? My gut tells me I blew 10 years of carbon build up out the exhaust and affected the O2 sensor but I've been doing some reading here and understand there are 2? and that it's not uncommon to have MAF issues with these. Oh, and I managed to keep a 21 mpg average as opposed to my fathers 23 hwy. Any suggestions (besides the obvious "slow down") would be much appreciated.

Thank you all in advance.

You might start with the following link:

http://us.lexusownersclub.com/forums/index.php?showtopic=52026

Choose the 2003 RX300 repair manual (similar to the 1999). This link will present you with several downloadable How To docs. I use these for my 2001 RX 300 with no problem. The SFI file provides many helpful suggestions for diagnosing your sensor issues. The 1999 RX 300 manual may be a little too general. It does not explain how to test each sensor, for example. Good luck!

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