yoshi

I have a 2001 Lexus RX300.

Engine check light + VSC light came on.

Took it to garage, the obd said 'OXYGEN SENSOR 1, BANK 1'.

I noted from a Lexus invoice from the previous owner oxygen sensor 1, bank 1 had been replaced recently. So I took it to Lexus dealer and they confirmed that oxygen sensor 1, bank 1 was faulty according to obd and put a brand new sensor in it under warranty.

Drove for 3 days and Engine check light + VSC light came on again.

So, I decided to clean the MAF. Cleaned it with electrical component solvent cleaner, put it back together (and reset the engine code by disconnecting the battery). 135 miles later, the engine check light + VSC came on again. It is definitely INTERMITTENT fault, as I can reset the ecu and drive for between 1-3 days before the engine check light comes on again.

Any ideas? I am aware of the petrol cap issue. However, I turn the cap and it 'clicks' a couple of times after refueling.

Should I try cleaning the air filter? There is a new one fitted 10 months ago, so I presume it's pretty clean.

Lexus can't really help me - they say they would need to 'try' a few things, which means they just swop parts and hand me a bill until they fix it.

Please help!!!!

Lexmex

yoshi,

Do you know the EXACT code you got, was it like P1071, P1133, etc?

I'd be curious to know (but no real way to know) what kind of sensor they used when they switch out the other one, as sometimes not using the OEM Denso can result in issues.

In addition, you could have an exhaust leak somewhere that is causing the sensor. With the actual OBDII code I could help you narrow down the causes.

yoshi

Yeah the code was showing 'lean fuel/ oxygen sensor' / oxygen sensor 1, bank 1. Didn't see a fault code on the obd.

Lexus then replaced with a DENSO product.

Today I removed the MAF for a 2nd time but this time cleaned with contact cleaner + cotton buds. Last time I just cleaned by spraying with contact cleaner.

alflash

HTH
https://www.clublexus.com/forums/sho...d.php?t=222005

Lexmex

Ah yeah, I remember those threads.

yoshi,

This is a list for P0171, which can show up as the Bank 1, Rear 1, though it doesn't mean that the O2 (or A/F sensor) is bad. Lexus should be able to have an advanced scanner to see the readings coming off of Bank 2 on the front and Bank 1 on the rear to see if the sensor is bad or not.

For P0171 you could have:

air intake (hose loose)
fuel line pressure
injector blockage
A/F sensor
MAF sensor
engine coolant temperature sensor (not likely)
gas leakage on exhaust system or leakeage on the exhaust itself
gas cap
IACV valve (see the stick at the top of the RX300 forum on gas mileage).

Now, I can tell you I get P0171 at least twice a week because my air intake system runs too lean (but that is because it is heavily modified). Abrupt cold weather can do this.

The only other codes for bank 1, sensor 1 are related to the A/F sensor (or O2 as you call it).

Having the code would definitely help.

yoshi

Thank you very much for your reply.

We OBDed it at my independant garage - it didn't give a P-code or whatever, just 'BANK 1, SENSOR 1'. Strangely the BANK 1 SENSOR 1 sat at about 2.8v with the ignition off. Bank 2 Sensor 2 sat at 3.0v exactly.

OK, so I go to Lexus and change the O2 sensor to a DENSO one.

I have now thoroughly cleaned the MAF and reset the codes - it seems these two issues are the most common cause.

What would your guess be if the lights come back on?

Lexmex

You'd have to check the code again and see. There is still some issues that it could be per my list above, assuming it is a P0171 error.

Now with your voltage on those sensors, they're okay. Where I woud worry is if it goes below 2.8 or above 3.8. There are some extenuating circumstances, where it can be below or above those figures (fuel enrichment and fuel cut, respectively). However, there is also a situation where if the volts remains at 3.3, there also may be a short. Thus, that may be a sign this is a P0171 error since the volts are within norm.

However, keep in mind, P0171 and even A/F sensor issues can be the result of temporary sensor readings, but I am leaning toward another issue as in the ones I mentioned in the list above.

There is a way that I can force a P0171 error on the highway by running the vehicle up to speed, letting off the accelerator, the air comes in hard though my lower air intake and that causes a lean condition.

yoshi

OK, thanks.

I'm going to see if my 2nd clean of the MAF yields any results. One thing I noticed was the screws on the MAF were secure but not super-tight. I have made them supertight...no idea if this makes any difference at all, but it would keep the MAF more secure I presume.

Otherwise, I will have to look at other options.....