HELP. Check engine light...

[gsujeff55]

Ok guys, need some quick help here. I have had a check engine light on for quite a while on my 99 ltd 4runner. Now, code its throwing is "engine lean" code. The thing has had horrid gas mileage since.

I figure its the o2 sensor, but would like someone to confirm it or say what else it could be. Also, how many o2 sensors are on it? I know there is one just after the cat, is there another?

Also, you guys know any good junkyard sites, or any other place i can get a descently priced o2 sensor?

Thanks in advance,

Jeff

 

[lee]

what code is it throwing specifically?

02 sensor or MAF?

 

[greasefingers]

A lean condition is caused by two things. A vacuum leak or a dead oxygen sensor. The output of most O2 sensors 0.1 volts to 0.9 volts. Rich condition is 0.9 volts. If your sensor is dead than using a volt meter could confirm this. At idle speed and with the engine running at temperature, one could back-probe the sensor and check for this valve to be pegged at 0 volts, meaning O2 sensor NFG. A good sensor will form a sine wave or fluctuate between these two extreme values as the idle speed is changed. If the computer receives a "lean condition" then the fuel management will control richer than normal resulting in a decrease in mileage.

 

[gsujeff55]

what code is it throwing specifically?

02 sensor or MAF?

Neither. Its throwing engine lean code....i don't remember the exact name or the code. But something to do with engine lean. Which i would assume it thinks that because the o2 sensor is shot and not reading right.

But i could be wrong i guess, i just dunno what other sensor could let the ECU know something was lean. I just think its getting that code and dumping tons of un-needed fuel in there causing my gas mileage to be crap!

 

[greasefingers]

And if Toyota is like other vehicles that I am familiar with, then the down stream O2 sensor does not affect the performance of the engine. It is used to predict when the catalysis is spent. The upstream one is the input to the computer used for fuel management. So if the upstream and downstream valves are the same then the catalytic converter needs to be replaced. I guess if both sensors were bad it then this could also produce a simular result?

 

[gsujeff55]

A lean condition is caused by two things. A vacuum leak or a dead oxygen sensor. The output of most O2 sensors 0.1 volts to 0.9 volts. Rich condition is 0.9 volts. If your sensor is dead than using a volt meter could confirm this. At idle speed and with the engine running at temperature, one could back-probe the sensor and check for this valve to be pegged at 0 volts, meaning O2 sensor NFG. A good sensor will form a sine wave or fluctuate between these two extreme values as the idle speed is changed. If the computer receives a "lean condition" then the fuel management will control richer than normal resulting in a decrease in mileage.

Thank you. Now, is there only 1 o2 sensor?

Let me make sure i read this right...if the voltage(at the o2) is staying at .1 or less...its shot...if it bouces around, its ok. Right?

 

[gsujeff55]

And if Toyota is like other vehicles that I am familiar with, then the down stream O2 sensor does not affect the performance of the engine. It is used to predict when the catalysis is spent. The upstream one is the input to the computer used for fuel management. So if the upstream and downstream valves are the same then the catalytic converter needs to be replaced. I guess if both sensors were bad it then this could also produce a simular result?

Right, thats what i thought...but i wasn't sure if it had 2 o2s or just used 1 to get cat deficiency readings and a/f.

 

[greasefingers]

You have at least two O2 sensors. I do not have your engine so I cannot be exact. The voltage should be steady under idle conditions and should be approximately half of the range or 0.45 volts. When you rev the engine the voltage will start to fluctuate.