I tired to search for help on this topic but i' not really sure what to search for.....

My 1999 SR5 4x2 4Runner threw up a check light the other day, a quick scan showed that the left bank of the engine was running lean, we reset it hoping that it was a one-time error but it came back the following week. The O2 sensor is ok and it seems like the ECU is what is giving the problem. The ECU is constantly getting the "high" voltage from the O2 which is giving the error but a replacement of the O2 didn't fix the problem, my friend's shop is thinking it may be a bad ECU but they don't want to get another one without being sure because of the high cost of a new ECU. Also if I replace the ECU will it affect anything else in my truck? Is the odometer mileage stored in the ECU also? can anyone help?!!?

thanks!

 

Which code did you get? P0171 ? Try cleaning the MAF. Search for it, you'll find a write up. Sometimes it works. It did on mine ('99 SR5 4x4)... Particularly if you have an oil type air filter. Also, the MAF may be bad, but try cleaning it first. Hey, can't hurt and all it'll cost is a can of electrical contact cleaner.

Good luck.

 

yep try cleaning it and then go from there

 

Ditto....sounds like P0171 System too Lean (Bank 1).....and BTW there is only one "sensor bank" on the 3.4L, it doesn't pertain to the cylinders on one side or the other at all. Do a search for that code and MAF cleaning and you'll find TONS of info on here about how to fix your issue. Also get rid of the K&N filter if you have one and use an Amsoil or Trueflow instead (has been shown as one possible source of MAF fouling).