CEL is on

[mmml4]

Got a 99 4runner 3.4 auto with the check engine light on. Had the code checked and it was a PO171 system too lean (fuel Trim). It only seems to do it when driven at hwy speeds for 30 mins or more. I have pulled the EFI fuse to reset it and as long as it is driven around town it does not come back on . Has anyone had this, any ideas.

 

[bowyer2002]

Could it be too lean from a dirty fuel filter?
Just an idea.

 

[raydouble]

I would clean the MAF sensor with an electronics cleaner, check for vacuum leaks and reset again. Code P0171 is for bank one sensor one of the heated O2 sensor.

Searching Google for "P0171 Toyota" yields lots of reading material,
I saw vacuum leak, dirty MAF, malfunctioning MAF and malfunctioning HO2 sensor or circuit wiring for any of the preceding.

 

[mmml4]

OK, so I cleaned and checked the MAF sensor and reset the cel. If it comes back I guess I'll go to the step. Thanks for the info.

 

[mmml4]

It looks like cleaning the MAF sensor did the trick.

 

[raydouble]

It looks like cleaning the MAF sensor did the trick.

Awesome, thanks for the follow up

 

[mmml4]

Guess I spoke too soon, its back . Now to get the code read again and start troubleshooting again. Life isn't a learning curve, it's a learning circle !

 

[mikeyb]

I am dealing with the same thing in my 80. So far I have replaced the fuel filter, the front 02 sensor, and fixed a vacuum leak. Still have the problem. Today I was able to borrow a friends ELM OBD reader and my data shows that the Intake Air Temp reads 140 when the engine is cold. I guess I need to replace the MAF

 

[XT Toyota]

Cleaning the MAF sensor for me happens everytime I change the oil. NAPA has a "special" MAF cleaner that is MORE gentle for the fine filiments that read the information back to the ECU. Don't get me wrong I have friends who use "electrical cleaner" and even brake cleaner and have never had issues. I had similar problem in the past and ended up changing the MAF sensor. Do any others here run a SCAN GAUGE II for diagnostics/gauges? Good Luck.

 

[radioridge]

Did you get this fixed? I'm in the same boat, have cleaned MAF, checked for vac leaks, replaced fuel filter. Light stays off around town but comes back on after a short time on the interstate.

 

[mmml4]

Well actually no, shortly after the CEL problem someone stole the catalytic converter twice. Had a spare the first time, now its running without the cat and of course I have the CEL.

Then the 4runner went off to college and since it runs fine I don't worry about it anymore.