vuvision

My wife's RX300 Engine Light popped on last week. I then took it to Autozone, the OBDII code is P0171 - Bank 1 (Before the Cat). I was told that this is the A/F sensor between the firewall & the engine.

1) I was able to locate the MAF sensor in front of the fan, but where exactly is this A/F sensor at the back ? Is it on the driver side or the passenger side ?

2) How much is the OEM A/F sensor ?

3) Can someone recommend an after market A/F sensor ?

Thanks in advance

Lexmexico

I posted before about this particular code. While it usually pops up with a loose gas cap, clogged air filter, insecure air flow to the engine, there is another culprit.

My K&N air filter has an oil base to it. After using the filter for about a year, that oil go on to the Air/Fuel Sensor just behind the airbox and before the throttle body. It sent the check engine light on and I read a P0171. I kept getting dogged by it even after we reset the light, because I could honestly not tell just what it was.

Finally, after contacing Lexus they suggested I take a look at the air/fuel sensor, and it was covered in the air filter's muck. I cleaned it off using brake dust cleaner, put it back in. I then, with the motor off, took out the EFI (No. 13 fuse) for a few seconds, put it back in, check engine light reset, no problems since.

vuvision

Lexmexico, thanks for your reply. My air filter is OEM which I've replaced a several months ago, but I will check and see if it's is installed properly tonight. I will also try to clean the A/F sensor as suggested.

My question is, where exactly is this A/F sensor ?

Thanks

Lexmexico

The sensor I am referring to is just after the air box. You will see a two silver screws placed diagonally on a black square piece. Unscrew these. Then, carefully lift this sensor out and disconnect the plug.

You will see a thin piece of metal wire running vertically. On one side you should see some crud. Clean this off with brake fluid cleaner. Others have suggested gumout or carburator cleaner, but brake fluid is what was recommended to me and it did fine. After you replace this and recrew it, head to the fuse box.

There is a No. 13 fuse (check your owner's manual) called the EFI. I think it is yellow and has a 10 AMP. Remove this with the car off and put it back in. Check engine light should go off.

VVT-i

Vuvision, I think P0171 is for system too lean, not the AF sensor. The P0171 is relate to Air flow meter like Lexmax said.

vuvision

Lexmex & VVT-i, thanks for your reply. I've just confirmed this P0171 code with a local Lexus Tech, and it is as you said, MAF sensor. I will clean out the metal wire as suggested before purchasing the MAF sensor.

Thanks for your help.

Lexmexico

When you get that sensor problem, a fuel trim lean code also pops up.

BurnishedGoldRX

According to Lexus repair manual, you might want to check fuel pressure, MAF sensor, coolant
temp sensor, and your heated o2 sensor. Was that the only code it gave? She didn't run out of fuel
anytime recently, did she? That would give the same code.