Taco emission fail (1 Viewer)

[BrotherRob]

My 95 Taco 3.4 failed the NOX test, barely.

I am getting a P0141, which is the downstream O2. AZ only does a sniffer test on 95s, as I understand it, the downstream O2 is just a monitoring devise and would not affect exhaust output. I really have no other known issues. There is no EGR, timing and fuel/air mixture is set by the computer.

My plan is to clean the MAF, air filter, PVC and throttle body but I don't see any of those having much of an impact. Unfortunately, AZ does not recognize a 95 as OBD2 compliant, so just correcting codes has limited value. The computer only shows the one error, so not much to go on. I'm not in a good position to throw parts at it until it passes. Anyone have any additional thoughts?

 

[coloradobound]

My 95 Taco 3.4 failed the NOX test, barely.

I am getting a P0141, which is the downstream O2. AZ only does a sniffer test on 95s, as I understand it, the downstream O2 is just a monitoring devise and would not affect exhaust output. I really have no other known issues. There is no EGR, timing and fuel/air mixture is set by the computer.

My plan is to clean the MAF, air filter, PVC and throttle body but I don't see any of those having much of an impact. Unfortunately, AZ does not recognize a 95 as OBD2 compliant, so just correcting codes has limited value. The computer only shows the one error, so not much to go on. I'm not in a good position to throw parts at it until it passes. Anyone have any additional thoughts?

Damn. May be cat. Friends cherokee w Carb needed a new cat to pass emissions here.

 

[ken_79-fj40]

The downstream 02 sensor is reading the results coming out of the converter. If it were lazy it could be the actual problem. Or you might need a new cat. I would replace the sensor first considering it's triggering a code and it could be the issue. They aren't too expensive aftermarket.

 

[40Habits]

Typically a failed catalytic converter does not cause this code.

The rear O2 sensor monitors the oxygen level in the exhaust gas and sends it to the ECM. The ECM adjusts the fuel injection time so that the air-fuel ratio is right for catalyst operation.

URD sells a simulator kit that cost as much as the O2 sensor and should fix the code.

Underdog Racing Development

 

[BrotherRob]

Typically a failed catalytic converter does not cause this code.

The rear O2 sensor monitors the oxygen level in the exhaust gas and sends it to the ECM. The ECM adjusts the fuel injection time so that the air-fuel ratio is right for catalyst operation.

URD sells a simulator kit that cost as much as the O2 sensor and should fix the code.

Underdog Racing Development

Why would one use a simulator rather than replacing the sensor?

 

[Brake Weight]

So you can run catless without a CEL. But it doesn't help with passing emissions.

 

[BrotherRob]

So you can run catless without a CEL. But it doesn't help with passing emissions.

Yep, not an option.

 

[40Habits]

The simulator might help you pass by fooling the ECM but you would not gain anything by using it. You would be better off replacing it with a stock 02 sensor. If the rear O2 sensor is bad it will affect your air-fuel ratio (rich/lean) and that affect the NOx levels.

 

[Brake Weight]

The post cat O2 sensor will make the engine run rich so that the cat can get heated up to work properly. A simulator will send a signal that it is hot already and it may or may not be.

 

[40Habits]

A simulator will send a signal that it is hot already and it may or may not be.

Were you agreeing or disagreeing with me?? You wouldn't do a smog test with a cold cat.

 

[Brake Weight]

Were you agreeing or disagreeing with me?? You wouldn't do a smog test with a cold cat.

If it's the cat is good, it should eventually heat up to pass the sniffer. If they just check the ECU, it'll pass.

 

[BrotherRob]

If it's the cat is good, it should eventually heat up to pass the sniffer. If they just check the ECU, it'll pass.

AZ does not test the ECU on 95s. 95 was a transition year, OBD2 was not required, even though Toyota installed OBD2 on 95 models, AZ treats them as non OBD2 vehicles. That's what makes this one a PITA, I can have no codes and still fail. So, without retesting, I have no way to tell if it's fixed.

 

[Kleatus]

Recently had the same code along with a CEL on my 95 2wd 3.4. The PO said he just replaced it last winter, and it did indeed look new. But it had no manufacturers name, no part number, no nothin', and wasn't working. Knowing him he got the cheapest thing he could find online, and it didn't last a year. I replaced it with a Bosch sensor and no issues since... You could get some of that "guaranteed to pass emissions" stuff they have at parts stores, then try and take them up on their guarantee. Or you could just spend 100 bucks on the right sensor, once you have eliminated other potential problems. They can get funky readings with exhaust leaks near the sensors too, look for that. You can also pull the sensor and crudely test it using a meter and a propane torch, but you cannot confirm that it is functioning correctly doing that, only "yep, it's fried" or "it LOOKS like it's working."