Only one o2 Sensor??

[Born to be Wild]

Hi everyone I just bought an 99 4Runner 4x4 V6 auto and Im having a very poor gas rendition so I started by replacing spark plugs,Air filter,Oil change etc etc but when i went down to replace my o2 sensors I only found one the up stream is this normal in a 99 4Runner?? please any advise

 

[Troybylt]

Yeah, that's normal for a non cali 4runner. One in the left header and one before the cat. Cali have a third I believe though.

 

[Ruiner]

Yeah, that's normal for a non cali 4runner. One in the left header and one before the cat. Cali have a third I believe though.

usually you have one before the cat, to measure engine performance, and one after to measure the performance of the cat, right?

 

[Ruiner]

usually you have one before the cat, to measure engine performance, and one after to measure the performance of the cat, right?

also i think Cali ones have two cats, an 02 sensor and an A/F sensor (instead of two 02 sensors)

 

[jeremyc74]

usually you have one before the cat, to measure engine performance, and one after to measure the performance of the cat, right?

That's the case on every federal emissions vehicle I've owned, and I'm pretty sure it's an EPA requirement.

Maybe Toyota did something different, but usually there's the upstream sensor to allow the ECU to adjust A/F ratio, and the downstream sensor to ensure the converter is working properly. I didn't know it was possible to do it any other way. The CA compliant vehicles have an extra converter, and more accurate sensors, but there's still just two of them. One upstream and one down.

I'd suspect this 4Runner has had some exhaust work and one was removed.

OP, do you get a check engine light? If not, does it light up for a few seconds when you start the truck? (Just to be sure the bulb is there and working).

 

[Ruiner]

Does the mid pipe look like this

 

[Ruiner]

If so you have a cali car and need a wideband (a/f) infront of the cat and a regular o2 after the second cat.

 

[Ruiner]

non CA vehicles have two regular o2's and one cat like this

 

[Ruiner]

That's the case on every federal emissions vehicle I've owned, and I'm pretty sure it's an EPA requirement.

Maybe Toyota did something different, but usually there's the upstream sensor to allow the ECU to adjust A/F ratio, and the downstream sensor to ensure the converter is working properly. I didn't know it was possible to do it any other way. The CA compliant vehicles have an extra converter, and more accurate sensors, but there's still just two of them. One upstream and one down.

I'd suspect this 4Runner has had some exhaust work and one was removed.

OP, do you get a check engine light? If not, does it light up for a few seconds when you start the truck? (Just to be sure the bulb is there and working).

for OBDII vehicles, yes. OBDI requires just a precat 02 sensor. and if you use some thing like EFIlive you can disable the downstream sensor on OBDII since it basically has no affect on how the ECM manages AFR

 

[jeremyc74]

for OBDII vehicles, yes. OBDI requires just a precat 02 sensor. and if you use some thing like EFIlive you can disable the downstream sensor on OBDII since it basically has no affect on how the ECM manages AFR

OBDII became mandatory in '95 I think, so his vehicle should have two sensors on it. So if the second one isn't there at all there should be a CEL, or it's been removed or disabled.

 

[Ruiner]

OBDII became mandatory in '95 I think, so his vehicle should have two sensors on it. So if the second one isn't there at all there should be a CEL, or it's been removed or disabled.

yup, it deff should be there somewhere, but that one wouldnt be the one affecting gas mileage even if it was deleted.

 

[TheDurk]

All 3G 4Runners are OBDII and have 2 sensors, before and after the cat or cats. If the second one is missing, and no P0420 or P0141 codes are set, then odds are there is a simulator box somewhere wired in to fool the ECM into thinking there is a working downstream sensor.

If your '99 is a Cali., it will have two cats and an A/F sensor before the first cat, but both 49-state and Cali. will have a downstream O2 sensor after the cat or cats.

 

[jeremyc74]

yup, it deff should be there somewhere, but that one wouldnt be the one affecting gas mileage even if it was deleted.

Very true. If the CEL has been removed or is burnt it could have a bad upstream sensor (or any number of other issues) that aren't showing themselves.

Figuring out what codes are actually stored would be my next step.

 

[gamefreakgc]

All 3G 4Runners are OBDII and have 2 sensors, before and after the cat or cats. If the second one is missing, and no P0420 or P0141 codes are set, then odds are there is a simulator box somewhere wired in to fool the ECM into thinking there is a working downstream sensor.

If your '99 is a Cali., it will have two cats and an A/F sensor before the first cat, but both 49-state and Cali. will have a downstream O2 sensor after the cat or cats.

This. It seems like O2 simulators are the "quick fix" for emission codes because the catalytic converters are stupid expensive for some reason to replace.

 

[Ruiner]

This. It seems like O2 simulators are the "quick fix" for emission codes because the catalytic converters are stupid expensive for some reason to replace.

they contain platinum and other precious metals.

 

[Born to be Wild]

Yes it is a Calif vehicle

 

[Born to be Wild]

Thanks everyone for your reply's I think that someone has tampered the system I bought this truck as a project I used to live in Beautiful California (LA Area) but because of my work I still go back and forth between California and Arizona so I decided to buy the truck in California I jump into the offer for the low mileage that it say it has Toy 4Runner 1999 V6 4x4 Auto Sport etc etc 123K Miles the interior was kind of destroyed which i already change to leather seats
I took a trip from LA to Vegas and from Vegas to Phoenix gas was pouring like if it had a hole in the tank making around 10 miles per gallon I took it to autozone they hook the tester and it gave 3 codes PO171-PO141-P1135 all these codes point to o2 sensor that's when I find out that I only have one its been already replace , yesterday I took the truck for a spin and a photo shoot close by and it seem that the gas miles has improve tremendously I still have to take it back to the autozone for a second reading the check engine light is missing and I'm in the process to fix it Now the question that I have is if I can incur in damages to the engine if I don't have that second sensor?

 

[TheDurk]

Thanks everyone for your reply's I think that someone has tampered the system I bought this truck as a project I used to live in Beautiful California (LA Area) but because of my work I still go back and forth between California and Arizona so I decided to buy the truck in California I jump into the offer for the low mileage that it say it has Toy 4Runner 1999 V6 4x4 Auto Sport etc etc 123K Miles the interior was kind of destroyed which i already change to leather seats
I took a trip from LA to Vegas and from Vegas to Phoenix gas was pouring like if it had a hole in the tank making around 10 miles per gallon I took it to autozone they hook the tester and it gave 3 codes PO171-PO141-P1135 all these codes point to o2 sensor that's when I find out that I only have one its been already replace , yesterday I took the truck for a spin and a photo shoot close by and it seem that the gas miles has improve tremendously I still have to take it back to the autozone for a second reading the check engine light is missing and I'm in the process to fix it Now the question that I have is if I can incur in damages to the engine if I don't have that second sensor?

None whatsoever. The only function of the rear sensor is to set the P0420 code when the cats are operating below efficiency allowing excessive emissions.

However, the P1135 is a front sensor fail code that suggests it may not even be in a working circuit (since it was recently changed), which could lead to the p0171 and excessively rich fuel mix and craptastic mpg. You need someone with some real understanding to figure out what was done to your engine control system and give it one that works.

 

[midge914]

So frome what I read it would be perfectly fine if you did the Rear o2 simulator and cut the exhaust and re-pipe it without a the sensor and just zip tie it up on the frame???

 

[TheDurk]

So frome what I read it would be perfectly fine if you did the Rear o2 simulator and cut the exhaust and re-pipe it without a the sensor and just zip tie it up on the frame???

No. The URD sim actually conditions the signal from the rear O2 and requires a working sensor in the circuit. I don't know if the sensor has to be in the exhaust or not.

Other simulators may not work that way. The simple DIY one does not. Of course, without a rear sensor somewhere you will get both a heater code and a signal code and a lit CEL.