Tacoma Oxygen sensor heater circuit P0031, MAF P0100, and High Volt P3100

[TacoBell07]

Getting really bad gas mileage.

I unplugged one O2 sensor and then started getting P0031, P0100, and P3100. Have cleared with scan tool and codes come back immediately.
One interesting thing is when unplug MAF sensor let it stall then start engine again there is no O2 sensor heater circuit code bank 1 sensor (AF ratio).
Already replaced MAF sensor did not seem to help in fact seems little worse but like hesitation.

Anyone have any ideas next thing is checking O2 AF ration sensor

 

[Will Evans]

I'm kind of in the same boat as you.
I recently got my frame replaced, and while they did that I had them put on new exhaust. Truck seems to be running great, but my mileage went down 10%. I used to get 550km before the refill light came on now the light comes on at 490km. It's not a huge decrease but it's one less trip to work and back per tank. Adds up, especially at $1.20/L
I'm thinking it's a combination of the colder weather (less tire psi - yet to top up) and the winter fuel.

Can you provide more info on your situation;
What model is your truck?
How much has your mileage decreased?
When did you notice it?
Any changes made to your truck?

 

[TacoBell07]

I did not have these codes until I removed the exhaust on passenger side to repair heat shield. The downstream O2 sensor was unplugged due to this.
270K on truck 4.0 L V6 and mpg has dropped dramatically after 100 miles only half a tank around town going 50 miles burns quarter of a tank roughly. Usually I thought bad upstream O2 Air fuel ratio sensors caused the worse gas mileage when compared to other sensors like MAF or TPS having issues.
Already replaced MAF and seems to run a little worse but can time some time for computer to compensate for those.

 

[Will Evans]

Hmmm well the fact that you didn't have the issue until you removed the exhaust, and O2 sensor would lead me to believe that it has something to do with the O2 sensor.
Is it possible a wire got damaged during the removal/install?
Did you try removing the battery to 'reset' the ECU?
If you have an IR thermometer, check up stream and down stream temps of the Cat. I've read that if they vary by more than 70°F, that's an indication of a blocked or partially blocked cat. It seem unlikely giving your situation but it's easy to do and rule out.
I've also read on other forums that it's as simple as replacing that sensor with a new one.

let us know how you make out.

 

[TacoBell07]

Removed battery power overnight made no difference. Cleared codes several times with scan tool codes come back within 5-10 secs of being cleared.
I wondered that but didn't find any damaged or broken wires. Continuity on downstream O2 sensor is good, downstream only one I unplugged yet the code is heater circuit malfunction on bank 1 sensor 1 which should be upstream AF sensor on passenger side from everything I've reviewed.
I have this type of thermometer I will try that, is there a certain temperature to check it at, I assume it should be checked at operating temp ?

 

[Will Evans]

Yes you would want to check it when it is running, but I think it's the sensor or wiring.

P0031 is the code you should to be paying attention to. I don't think a new MAF sensor was required.

P0100 & P3100; I'm guessing are just secondary faults caused by the bad sensor or harness.

What puzzles me is you say you only removed the bank 1 sensor 2 (down stream) but the P0031 code indicates an issue with the bank 1 sensor 1 (upstream). I don't know the configuration of the wire harness, but I would be looking at that bank 1 sensor 1 and it's connections.

See this link here: https://www.obd-codes.com/p0031

And here is the wiring diagram I was looking at: https://www.autozone.com/repairguid...al-Wiring-Diagram-2006-1/_/P-0996b43f80378c3d

Hope that helps.

 

[TacoBell07]

Replaced O2 sensor and the code did not come back on. Somehow the O2 wire got pinched it appears and made it go bad. Wish would have known this was issue as replaced the entire O2 sensor. Good reason to inspect wiring thoroughly before replacing and do check with multimeter.