"Check Engine" light keeps coming on with aftermarket upstream O2 sensor.

[Benski]

I had my check engine light (CEL) come on last week. I quick diagnosis showed it was the upstream O2 sensor. I replaced it with an aftermarket "direct fit" replacement. I reset the CEL and after several times turning the engine on and off and driving, the CEL came back on. A diagnosis showed it was the O2 sensor again. Has anyone has this same issue? Will it eventually stay off if I keep resetting it? What aftermarket sensor has worked for you? Thanks.

 

[LittleCaesar]

Try a Denso first, or OEM.

 

[jgue467]

What CEL code does it set? Same code before and after? Any pending codes? :cowboy:

 

[RS Dude]

Always best to replace o2 sensors as a set, like your brake pads.:rockon:

 

[octanejunkie]

When is the last time you cleaned your MAF sensor?

 

[Benski]

So before I get a chance to order a Denso O2 sensor or clean my MAF I go to run an errand, and on the way back I look at the dash and see the CEL is off! I've never had a CEL go off without a reset. I'll update if there is any change.

 

[Benski]

Damn light came on again a day later!

 

[ridefast]

What code are you getting? po171?

 

[Ryance39]

Is the wire badly damaged by chance?
Try replacing with a Denso.
I have also always heard to replace both if one goes.

 

[4running4]

Hello all, I’m working on my son in laws new to him, 2000 4 runner 3.4 2 wheel drive.

The check engine light is on so I will be replacing both O2 sensors and doing a timing belt replacement while I’m at it.

Where do recommend buying the sensors from? I only want denso (OEM I believe).

Thank you and sorry if I jacked the thread.

 

[firemanj92]

Hello all, I’m working on my son in laws new to him, 2000 4 runner 3.4 2 wheel drive.

The check engine light is on so I will be replacing both O2 sensors and doing a timing belt replacement while I’m at it.

Where do recommend buying the sensors from? I only want denso (OEM I believe).

Thank you and sorry if I jacked the thread.

Amazon for Denso/OEM sensors or if you have an AdvanceAuto/carquest as they always have coupons 20-30% off

 

[4running4]

Amazon for Denso/OEM sensors or if you have an AdvanceAuto/carquest as they always have coupons 20-30% off

Thank you! I have not worked on a 4 runner before.

I’m finding denso’s with part numbers 234-4162 and 234-4169, sound like the right ones?

* editt* The 4162 looks right, not the 4169. I thought there were 2 of em

 

[firemanj92]

Thank you! I have not worked on a 4 runner before.

I’m finding denso’s with part numbers 234-4162 and 234-4169, sound like the right ones?

If its 50 state/CA emissions then 234-4153 (downstream) and CA 234-9002/9003 upstream- CA vehicles have a Air/Fuel sensor.

234-4161-non CA 2wd
234-4154/4155non CA 2wd

You can pull it as it's 2 14mm nuts and check the numbers etched around the body

 

[4running4]

Thank you very much!

 

[4running4]

If its 50 state/CA emissions then 234-4153 (downstream) and CA 234-9002/9003 upstream- CA vehicles have a Air/Fuel sensor.

234-4161-non CA 2wd
234-4154/4155non CA 2wd

You can pull it as it's 2 14mm nuts and check the numbers etched around the body

Thanks for the info! those 2WD numbers on amazon say they will not fit my vehicle. I’m going to start a new thread so I don’t mess with the OP.

 

[4running4]

Put it up on the lift last night and the O2 sensors look new (one in front of the cat and 1 behind), hard to tell what brand. Went to auto zone this morn and pulled a P0171 code.

 

[4running4]

Exhaust smell is strong sometimes, sulfur-ish. Check engine light started to flash on the drive home this morn.

 

[TheDurk]

If its 50 state/CA emissions then 234-4153 (downstream) and CA 234-9002/9003 upstream- CA vehicles have a Air/Fuel sensor.

234-4161-non CA 2wd
234-4154/4155non CA 2wd

You can pull it as it's 2 14mm nuts and check the numbers etched around the body

Not true. The numbers on the body have no relation to the p/n. The same body is used for many p/n's as they vary mainly by wire length.

Also, the nuts are stainless M8-1.25 and they take a 12mm wrench if they are OEM nuts.

To be sure of part number, you need year, transmission, engine, 2wd/4wd and Cali or Federal in '99 or '00.

Go here:

http://densoautoparts.com/find-my-part.aspx

P0171 and sulfur smell is more likely a MAF issue anyway. Start by cleaning it.

 

[4running4]

Thanks for the link!

So my understanding is the A/F sensor is only a calif thing. It does not show an A/f sensor application for anything but calif. models.

So that means I have two O2 sensors, 1upstream of the cat and 1 down stream, yes?

Just don’t want to order the wrong stuff.

 

[TirePro]

Downstream Bank 1 Sensor 2 is DEN 2344154

Upstream Bank 1 Sensor 1 is DEN 2344161

Approximately $90 each from NAPA