Researcher

I have a 2000 Tacoma with the 3.4L Engine with CA emissions

I have been getting the P0171 diagnostic code and was looking for a little help on it. I know it is not the MAF because it is literally brand new and I tested if using a code reader that lets me read live data. The sensor is reading correctly according to the Haynes manual I have. I have also replaced the rear 02 sensor and the code is still there. The reason I replaced the rear o2 sensor is that it showed no voltage reading on the code reader, it is my understanding it should read between .2 and .9 volts if working. After replacing the rear sensor it now read between that range.

I then looked at the voltage reading for the front sensor and it says 3.298 volts and it didn't change at all when driving and since I though o2 sensor where supposed to read between .2 and .9 volts I figured it was bad as well so I changed it but it still reads in the same range but now it changes between about 3.5 to 3.26.

My question is what should the o2 sensors read when view live data on a code reader?

Also where can I get and FSM most of the links I tried where no longer active?

I have also done a vacuum test using the smoke method and I didn't see any leaks. I also tested the coolant temp sensor and it seem good as well. I have tried to clean the MAF but it didnt change anything and I didn't expect it to since the readings were good and the sensor is new.

Any help greatly appreciated.

r34sklnnsn

Have you changed the fuel filter. It may be dirty not allowing adequate fuel threw.

Researcher

Yes I changed the fuel filter, air filter, and spark plugs

youngtoyotatech

So your sensor before the cat is actually a air/fuel ratio sensor. 3.3 volts is normal. So you are addressing a lean condition. With MAF good and no vacuum leak. I would suspect fuel delivery(pressure or injectors) or exhaust leak before the front sensors.

Researcher

Thank you very much for the af sensor clarification. I will check the fuel system next. I will check overall fuel pressure and if that is bad then I will check fuel pressure regulator then check fuel pump. If fuel pressure is good then I will check injectors.

Am I missing anything else to check?

Also is there a place to get an FSM somewhere?

TheDurk

You got good advice. If fuel system checks out ok, I'd try a known good MAF. Sometime they test good but aren't.

Toyota just killed the second online FSM source. (Boooo!)

It's still available here (download it while you can!):

http://web.archive.org/web/201011270...SIL/index.html