Siennna 2000 high fuel trims error p0171

Thanks for the detailed reply.

has anyone tried cutting a hole inside the Sienna to get to the fuel pump?

here are snap throttle charts for sensor 1 and sensor 2

b1s1


b2s1

update:

okay finally got chance to run the fuel pump tests. made access panel inside car. LOL

meter set to DC V
with KOEO, red probe to fuel pump postive. black probe to chassis ground I am getting 12.99V to 13.03V

with KOEO, red probe to fuel pump ground, black probe to chassis ground I am getting 200mV

meter set to 20A setting with red wire in 20A spot on meter
with KOEO, red and black probes hooked up to EFI 15 amp fuse connector in engine compartment I am getting 1.8A at Key on and 5.5 amps at KOEO

Please let me know what I should try next? thx

Just a quick FYI: Toyota does not use a KOEO pump prime like a lot of other manufacturers. Instead they use a "Circuit Opening Relay" to activate the pump when the key is turned to ignition.
You'll have to jump the pump if you need to run tests on the fuel system with the engine off.

Looking at everything, I don't think it's the AFR sensor or a vacuum leak. While I wouldn't rule it out, the fact that your trims don't get noticeably worse as you increase engine load kind of led me away from thinking it's the fuel pump.

For some reason, I keep coming back to the MAF.
Did you replace the MAF with an OEM Denso model? Or is it a 3rd party manufacturer? I find that the aftermarket MAFs often don't give the proper readings, and can keep a lean condition going. Even if the sensor itself is good, it may be that the wiring is compromised.
I might be able to get MAF readings for different RPM values from a known good '06 Sienna.

The_Floss wrote: Just a quick FYI: Toyota does not use a KOEO pump prime like a lot of other manufacturers. Instead they use a "Circuit Opening Relay" to activate the pump when the key is turned to ignition.
You'll have to jump the pump if you need to run tests on the fuel system with the engine off.

That is good to know. that was my main worry. I was not getting any fuel pressure with KO.
fuel pressure only with engine on and also if I jumped the fuel pump with engine off.

The_Floss wrote: Looking at everything, I don't think it's the AFR sensor or a vacuum leak. While I wouldn't rule it out, the fact that your trims don't get noticeably worse as you increase engine load kind of led me away from thinking it's the fuel pump.

For some reason, I keep coming back to the MAF.
Did you replace the MAF with an OEM Denso model? Or is it a 3rd party manufacturer? I find that the aftermarket MAFs often don't give the proper readings, and can keep a lean condition going. Even if the sensor itself is good, it may be that the wiring is compromised.
I might be able to get MAF readings for different RPM values from a known good '06 Sienna.

MAF was replaced with new toyota oem one. you said it could be wiring issue. How can I test that?

also what about exhaust leak? can that cause the high fuel trims? how to test?
btw exhaust is after the air fuel sensors correct?

check the pcv circuit... leaking pcv can cause positive fuel trims at idle. I read that you did smoke test with negative results. Might not be a hose or grommet leak. PCV may be stuck open. I would have expected better LTFT at 3000 rpm. Its worth checking to rule out.

You are absolutely right that an exhaust leak can contribute to a P0171 code.
In fact, I had an issue on my '03 Camry where the flex pipe had a major leak, in conjunction with a dirty MAF.

Prior to fixing the exhaust, I had high positive fuel trims at idle that would increase as load increased . After I fixed the exhaust, I had negative fuel trims at idle that would change to high positive trims under load. Cleaning the MAF brought everything back to normal.

As for testing the MAF wiring, a couple things come to mind:
With a cold engine and KOEO, pull up the Intake Air Temperature and Ambient Air Temperature live data. These should be identical or extremely close. Since the IAT sensor is integrated to the MAF, if there's a big difference then it's probably either the sensor or the wiring.
I just realized that the '06 Sienna MAF data won't be useful to you, because the '00 Sienna is a 3.0L while the '06 is a 3.3L, so that's out.
You can look at the harness and the plugs for the MAF and see if there is any corrosion or breaks in the line.
As for actually testing the circuit, Paul has some videos on scoping a MAF. Maybe this one will help.

update:
IAT was reporting 95 degrees which is almost same as temp today in NYC so that seems good. ECT was 85 degrees

here are my readings from the MAF connector using DWM.
it has 5 wires
blue/yellow and brown wire gave me 5.04V (first two wires on harness) seems like they are for the IAT
black/yellow wire and red wire give me 12.36V (last two wires on harness)
signal wire test (middle wire) with red wire for ground I am getting:
idle 1.4v
3000 rpm 2.1v
snap throttle 2.7v

Ill try to do another smoke test by piping it at the front air fuel sensor and then back tailpipe when I get the chance.