99SR5

iTrader: (1)

ok the code is P0171 and it says the system is too lean

so what is it

Greedy

Bad 02 sensor maybe??

99SR5

iTrader: (1)

yeah thats what it is but im trying to figure out which sensor it is

fireteacher

front is all that matters, clean the MAF(search) sensor also

hupptoy

When I had that code, it was a dirty/bad MAF most likely caused by my K&N. Well, probably caused by me putting a little too much oil on the K&N when I re-oiled after cleaning...

This was long before I *found* online forums, so my MAF was replaced, but a cleaning would be the first thing to try.

Do a search for cleaning the MAF sensor.

hupptoy

MTL_4runner

Clean the MAF first, if that fails, replace it and if that still doesn't work then replace the front O2 sensor.

MAF cleaning process:
http://www.4x4wire.com/toyota/mainte...tenancep5.html

nrgetic99

Its an air leak downstream of the MAF.

I would put good money on that.

I got that code after I installed my SC. Seems I had a bad throttle body gasket.

Could not see a problem.

Start at throttle body and work back toward airbox/maf.

David

gpcollen1

Mine was the MAF - found that after I replaced the O2. Start with cleaning the MAF - like MTL 4runner said...

WATRD

P0171
System too Lean (Fuel Trim)

Air induction system

Injector blockage

Mass air flow meter

Engine coolant temp. sensor

Fuel pressure

Gas leak on exhaust system

Open or short in A/F sensor (Bank 1 sensor 1) circuit

A/F sensor (bank 1 sensor 1)

ECM

P0171
When air fuel ratio feedback is stable after warming up engine,
fuel trim is considerably in error on RICH side (2 trip detection
logic)


When the DTC P0171 is recorded, the actual air–fuel ratio is on the lean side. When DTC P0172 is recorded, the actual air–fuel ratio is on the rich side.

If the vehicle runs out of fuel, the air–fuel ratio is lean and DTC P0171 is recorded. The MIL then comes on.

If the total of the short–term fuel trim value and long–term fuel trim value is within ± 35 % (80°C (176°F) or more), the system is functioning normally.

The A/F sensor (bank 1 sensor 1) output voltage and the short–term fuel trim value can be read using the OBD II scan tool or TOYOTA hand–held tester.

The ECM controls the voltage of the terminals AF1+ and AF1– of the ECM to the fixed voltage. Therefore it is impossible to confirm the A/F sensor output voltage without OBD II scan tool or TOYOTA hand–held tester.

WATRD

Cleaning the MAF will fix this 90% of the time.

99SR5

iTrader: (1)

but my CEL isnt on right now it turned off. should i still clean the MAF. how will i know if it worked should i just go ahead and buy a new front O2 sensor and clean the MAF just to make sure.

WATRD

Clean the MAF. It's simple, needs to be done from time to time anyway and may help to prevent a reoccurance of the problem. Hold off on the O2 sensor until you are sure it's needed.

99SR5

iTrader: (1)

well im getting about 180 miles per tank full and its pissing me off

midiwall

So am I around town and in stop & go (about 13.5mpg). I'm getting 18.5 on the highway.

Now, I KNOW what's causing my mileage issues, and it may be similar to what's causing yours. We all talked about a lot of stuff in your other thread, and now that you have to code we can start working through the list.


First thing - like everyone has said - clean the MAF. Have you yet?

Past that, it MAY be your front O2 sensor - that's what's screwing me up. It's causing the engine to run rich which is just wasting fuel. But, like Rob said, do NOT go after that until you clean the MAF.

So, have you cleaned the MAF yet?

DoubleZero4x4

When my front O2 sensor went there was an additional code along with the P0171. A search of YT should tell you what it was.

*clears throat before echoing*

Clean your MAF

99SR5

iTrader: (1)

im doing it either tomorrow or this weekend. i gotta find the cleaner and give it a shot

99SR5

iTrader: (1)

ok just cleaned it nice and good. i took it for a quick drive and it feels a little better ( might just be my emagination). so is that it, i dont have to unplug the battery to reset the computer do i?

MTL_4runner

Only if your CEL is still on (otherwise the ECU will relearn with the cleaned sensor).

midiwall

...but it may learn faster if you clear the trims first (by resetting the ECU, by either pulling the EFI fuse or pulling a battery cable).

MTL_4runner

I agree.