02 sensor replacement???

[TheDurk]

dammit i wish i had paid full attention to this along with the fact that you are in NJ. It's plain as day i have two cats but before even glancing under there I just assumed my single-owner VA bought car was a 49 state vehicle and ordered the 49-state Denso 234-4161. And now that I'm looking at it, it's not even an A/F, it an O2. Stupid, stupid.

Today i had finished the rest of the job (to be fair, the hard part taking off those corroded nuts) and couldn't get the plug to plug up... after failing for a few minutes I thought to compare the old and new plugs and sure enough the config of the new plug was different. I should have bought the 234-9003. I even compared the pics on Amazon too, it's the sensor with fewer holes in it and the damn thing costs twice as much.

Oh well, at least I didn't damage the threads on the studs and once my new one comes in, should be a cinch to put in.

Thanks for all your helpful posts on this subject. Hopefully no one else will make the same silly mistake considering the wealth of knowledge available.

That's for the 5-speed, right?

Find My Part | DENSO Auto Parts

 

[wjamyers]

That's for the 5-speed, right?

Find My Part | DENSO Auto Parts

Yep. I put in the new part last night. clip was a cinch to attach. My new 13 mm nuts were ready to go with lock washers. 5 minutes, torqued to 14 ft-lbs, reset the ECU and went for a 40 minute drive. No CEL. All of your posts were invaluable. If I'd paid attention to you more closely, you specifically said P1135 = A/F = Cali spec = Denso 234-9003.

P1135 is the A/F sensor heater circuit. Very specific--it has to be the sensor or the wiring--and you would have to be a real F/U to mess up the wiring doing a TB. It's all at the other end of the engine on the exhaust pipe and goes rearwards to the ECU. Cleaning is beyond useless--you can't heal a fried heater. Get a new OE Denso sensor off of Amazon and call it a fluke. Get the Denso part number here: Linky and then search Amazon (or just Google it).

Thanks again.

 

[MWRUNNER]

Hi Guys need some help. 2001 4runner V6 SR5 Cali 118k AUTO 2WD driving me bonkers. I have the P0171, P1130, P0125 as of right now. Ive already replaced the A/F with a Denso 234-9002 and replaced the MAF. Still have the codes. Engine is running crazy rich dumping gas:

Freeze Frame:
FuelSys1: CL_Fault
SHRTFT1:% 20.3
LONGFT1:% 39.8
O2B1S2: 0.955
O2B1S1: 3.307

My next move is to replace the downstream O2 (B1S2) thinking that its dying and defaulting lean even though the engine is running rich. Not sure what else to do. Im worried if I keep driving going to dump to much fuel into my Cat and blow it up. Another thought is need to check O2 & A/F harness wires for continuity I guess. Let me know thoughts and tips.

Thanks!
M

 

[Black798]

Freeze Frame:
FuelSys1: CL_Fault
SHRTFT1:% 20.3
LONGFT1:% 39.8
O2B1S2: 0.955
O2B1S1: 3.307
M

Looks to me like the problem is with sensor 1. An O2 sensor usually should read between .1 and 1 volts. .1 being a lean condition and 1 being rich. Also while the motor is running off you watch the live data on your scan tool the reading should jump between lean and rich about 1 time ever second. The P1130 code is saying your A/F readings are not in the right range. Which makes sense because sensor 1 is three times normal. Your theory about sensor 2 going bad could be the case but it's still giving a rich reading and if it is after the cat it won't have any effect on the fuel mix. It's odd that it threw the P0171 code seeing as it says the system is too lean. It could also be your ect sensor (P0125 is "insufficient coolant temp for closed loop.") I would check that sensor first and then off that checks out I'd go back to the sensor you replaced and say it was defective from the start. Hope this helps

 

[MWRUNNER]

Thanks for the info [MENTION=121903]Black798[/MENTION].

So I went ahead and replaced the downstream O2 sensor yesterday and reset the ECU. Lights came back on again after almost 100 miles. Its giving me P1130 only now. Below is the data at warm idle:

FuelSys1: CL
ECT: (F) 190
SHRTFT1:% 19.5
LONGFT1:% 0.0
O2B1S2: 0.800
O2B1S1: 3.319

I didn't have a chance to watch the live data with engine off, like you mentioned. But i did see it subtly fluctuate at idle. Im at a loss here. I guess my thinking is maybe there is a wiring harness issue for upstream A/F. Thanks again for the tips and appreciate any more thoughts/tips you might have.

M

 

[Black798]

Thanks for the info [MENTION=121903]Black798[/MENTION].

So I went ahead and replaced the downstream O2 sensor yesterday and reset the ECU. Lights came back on again after almost 100 miles. Its giving me P1130 only now. Below is the data at warm idle:

FuelSys1: CL
ECT: (F) 190
SHRTFT1:% 19.5
LONGFT1:% 0.0
O2B1S2: 0.800
O2B1S1: 3.319

I didn't have a chance to watch the live data with engine off, like you mentioned. But i did see it subtly fluctuate at idle. Im at a loss here. I guess my thinking is maybe there is a wiring harness issue for upstream A/F. Thanks again for the tips and appreciate any more thoughts/tips you might have.

M

Im with you on checking he wiring harness and making sure all the connections are clean and water tight. The best way I have found to test one of those sensors is to put the trans in neutral, hold the brake, and hold the engine at around 2500 rpm for a minute or so. This just ensures that the sensor is getting enough flow and heat to be working optimally. You may also want to check the front sensor for the proper resistance, that will give you a pretty good idea if its just a dud or not. There's plenty of write ups on testing those on google. Worst case scenario Id say replace that front sensor again and you should be good to go since your ect sensor is giving a good reading and everything else has been replaced.

 

[NeptuneBeach]

I just replaced mine with a Denso sensor. It was truly a quick job AND the CEL went off in addition to the VSC off light too. Weird how the VSC light would come on....

 

[TheDurk]

I just replaced mine with a Denso sensor. It was truly a quick job AND the CEL went off in addition to the VSC off light too. Weird how the VSC light would come on....

It's the '01-'02 Christmas tree. Some engineer decided people were ignoring CELs, and wired the the VSC to come on too.

 

[Teedeejr]

Looks to me like the problem is with sensor 1. An O2 sensor usually should read between .1 and 1 volts. .1 being a lean condition and 1 being rich. Also while the motor is running off you watch the live data on your scan tool the reading should jump between lean and rich about 1 time ever second.

This is good info. I'm struggling to squash my P0171 code and was thinking of replacing the front sensor. I watched the live data this morning and i'm pretty sure the sensor was staying between .1 and 1 with those wild swings every second.

Should I test the resistance at the sensor? Will that tell me if it is bad?

I've had the code with the original MAF and an autozone MAF (refurb), I've cleaned the TB (I did not remove the whole body though). I'm getting almost 19 mpg, but once I clear the code, it returns after about 20 miles of driving.

Any suggestions?

 

[NVAGVUP]

Suggestions:
I wish everybody (not just you) would stop with the '02 sensor'--It is an O2 or o2 (chemical symbol for atmospheric oxygen, sort of) but NOT an 02. This makes searching even less productive than it otherwise might be--for yourself and others who may come along later. Same applies to the DTC's, except backwards: it is P0171 NOT PO171 or po200. I hope this comes off as intended to be helpful, rather than picky.

Please post SOME data on your machine, at least year and engine and Cali. spec or not. You will get more and better help. Putting this in the sig is a good idea.

With that out of the way, if you really have 100K+ on your front sensor, changing it is probably a good idea. I wouldn't do the rear one unless I had a P0420 or other rear sensor specific code. Rear sensors should not affect either the running of the car or either of the DTC's you have.

I would also give the throttle body a good cleaning, just because it is easy, cheap, and might help. Then seafoam it to clean places you couldn't get to directly. Put in the new front sensor, reset the ECU and see what happens. A quick peek at the MAF might be worth it, too, depending on how effectively it was cleaned the first time.

There are still a lot of things that could cause these codes. If the CEL comes back on, post back with the codes, the freeze frame data, and the engine particulars. Freeze frame data is very useful in the case of P0300 and P0171.

I am no expert--I just take care of my own cars--but I'm think I'm solid here. If a pro wants to overrule me or make better suggestions, that's ok.

Check engine, o2 sensor and various xmas trees of warning lights on Gen 3 2002 T4R 188,000 mi. were a mystery as truck always ran well. Had codes run and got the usual o2 sensor codes, evaporative system [evap system would mean dropping tank to check etc] codes from VIP. checked the o2 sensor and it was good. Truck always ran well other than losing VSC when idiot lights came on.

Finally just ignored the warning lights [check engine, abs, VCS, airbag, battery,] which would come on and go off intermittently, sometimes for minutes, sometimes for days, never in any regular pattern-and drove the truck. Even drove from Maine to Montreal over the mountains with the idiot lights doing their thing sometimes; [without a spare battery and battery light on] without missing a beat. My gut and having driven the truck for all of its 15 years led me to believe it was the electronics and not physical mechanics that was setting off the warning lights.

Then last week my headlights and Fog lights suddenly went out one night. After some good advice from 'TheDurk' and others the DRL relay and the Lamp Relays were checked, found shorted and replaced. ALL WARNING LIGHTS FINALLY STOPPED FLASHING and check engine, VSC, lights are now off and haven't come back [except on start up check]. crossing my fingers. I stop driving this truck when either me or the T4R dies. Kind of pisses off my bride of 40 years, but the fact that there is no truck payment eases her anger over my dropping a grand or so a year into keeping it running against all odds [Maine snow and salt are biggest enemy].

Leads me to believe that maybe some codes can be caused by shorted circuits on electronic components..........any credibility to that?

Never had that problem way back when on my '58 392 Hemi coupe or my '73 mechanical fuelie Tii, which used mechanical means of control, had real gauges that meant something [and sucked massive amounts of fuel].

 

[Dozerman]

You mention first removing the sensor and feeding it up over the pipe to allow access to the connector with the Cali set up. If your 99 4runner is not a Cali set up then what is the easiest way to get to the connector? I am unable to get my fingers on the connectors from underneeth the vehicle.
Thanks

 

[catrains]

This is good info. I'm struggling to squash my P0171 code and was thinking of replacing the front sensor. I watched the live data this morning and i'm pretty sure the sensor was staying between .1 and 1 with those wild swings every second.

Should I test the resistance at the sensor? Will that tell me if it is bad?

I've had the code with the original MAF and an autozone MAF (refurb), I've cleaned the TB (I did not remove the whole body though). I'm getting almost 19 mpg, but once I clear the code, it returns after about 20 miles of driving.

Any suggestions?

the 171 code means a lean condition can be vacuum leak or low fuel pressures. intake manifold and exhaust leaks can create this code.

the MAF can create this but most times will throw other codes. using a frequency meter this can be checked to determine if the flow is being measured properly and a scan tool that is with the ability to measure the MAF flow of air. leaks on the air intake piping after maf can cause this.

with a scan tool watching the O2 voltage and using a propane gas or starter fluid you can check for the intake leaks after the maf.

O2 sensor should be replaced @100-130K miles. with the A/F sensor those do fail under 100K miles because they run at 1000 deg F.. much higher than the O2 sensors.

 

[mtbtim]

O2 Sensor Replacement

Hey Dudes,

Whether you're addressing a check engine light issue or looking for an improvement in your gas mileage, this video will show you how to replace your upstream and downstream O2 sensors. On the 96-98 3rd Gens, the upstream sensor is an O2 sensor. On the 99-02 3rd Gens, the upstream sensor is an Air/Fuel sensor.

From [MENTION=10169]TheDurk[/MENTION]:
Exception for '99 and '00 Federals, which also use the O2 upstream. '99 and '00 Cali. models, which were sold in about ten states, used the A/F upstream.

Not to be picky, Tim, but some people get confused by this.

<iframe width="560" height="315" src="https://www.youtube.com/embed/CtngAVxJxkE" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>

 

[TheDurk]

Hey Dudes,

Whether you're addressing a check engine light issue or looking for an improvement in your gas mileage, this video will show you how to replace your upstream and downstream O2 sensors. On the 96-98 3rd Gens, the upstream sensor is an O2 sensor. On the 99-02 3rd Gens, the upstream sensor is an Air/Fuel sensor.

Exception for '99 and '00 Federals, which also use the O2 upstream. '99 and '00 Cali. models, which were sold in about ten states, used the A/F upstream.

Not to be picky, Tim, but some people get confused by this.

 

[mtbtim]

Exception for '99 and '00 Federals, which also use the O2 upstream. '99 and '00 Cali. models, which were sold in about ten states, used the A/F upstream.

Not to be picky, Tim, but some people get confused by this.

Thanks for the correction Durk.

 

[scrapper]

Cleared the codes after replacing the A/F sensor. (Denso 234-9002 Air Fuel Ratio Sensor) I really struggled with disconnecting the wiring harness. The two bolts were effortless. After one partial turn w/ the 12mm socket I unscrewed them by hand. The wiring harness, on the other hand was killing me. The tiny retainer latch you have to push in while pulling the plug out is on the top so lying under it trying to do this was a pain until I accidentally broke the clip that holds the female end of the plug to the bracket. That made everything better. It allowed me to rotate the plug, see where exactly I need to push and out it came. Then I just zip tied it to the bracket.

Thanks to the info here I stayed the course and got it knocked out.

 

[Always Wanted One]

02 sensor replacement

Does the smell of rotten eggs going up hill always mean a cat replacement or can it still just be the 02 sensor?

 

[Lastplace]

CEL came on today, P0420, should I replace the 02 first? Local dealer said most runners that come in are Cali models. Mine is, 2 cats.

 

[eddielasvegas]

Raised in VB and left many years ago, but still miss it at times. FCHS/ODU grad.

I'd say replace the O2 sensor to see if fixes your problem. < $50 and maybe 30 mins work makes it an easy decision if it were me.

Good luck,

Eddie

CEL came on today, P0420, should I replace the 02 first? Local dealer said most runners that come in are Cali models. Mine is, 2 cats.

 

[TheDurk]

Does the smell of rotten eggs going up hill always mean a cat replacement or can it still just be the 02 sensor?

Well, if you don't fix it soon, it WILL be the death of the cat. It is either a physical fail in the cat or the FRONT O2 sensor is injecting too much fuel. Worth a try to do the front sensor first, but I don't give it good odds, especially if it has been doing this for a while.