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Toyota Prius Accelerator pedal position (APP) sensor

The Check engine light on my 2006 Prius came on and I used my OBD reader to determine the code was P1121 - “Accelerator pedal position (APP) sensor - range/performance problem”. I cleared the code to see if it would register again and a few weeks later same code showed up, but after driving it awhile the check engine light went out with out me clearing it and it remains off. The car drives normally with no other problems and when I monitor the APP sensor output I don’t see anything particularly unusual. I can spend the $300 to have a new pedal installed, but I’m not sure there’s problem especially if Toyota’s design allows for a non-catastrophic failure mode.

My question is how does Toyota’s engine control module manage a failure of the APP sensor? Is there a fail safe backup or is there potential for loss of throttle control like we heard about years ago in the news?

The loss was typically due to carpets, sometimes to driver error.

But why not fix it?


Sorry to inform you, but your code reader is wrong

P1121 is actually a code for the coolant flow control valve

I can’t post this TSB, unfortunately, but you can look it up on your own

But google EG001-08 pdf

He’s right. Here’s the TSB:

“But why not fix it?”…Good question - I guess my answer to that is if I can get information that says a failure would be a soft failure that would leave the vehicle in a safe condition, I would wait to see if the error code reappeared. The error code only showed up twice and has not yet come back. It could be that replacing the APP sensor wouldn’t fix the problem if there’s another source such as a loose connector or electrical noise. That’s why I’m asking if anyone knows what happens if the APP sensor fails.

I did have the recall work done several years ago on the pedal shape and carpets that were the potential sources of the unexplained accelerations.


huh . . . ?

You told us what code you have, and we told you what p1121 means

It seems that your code reader is wrong

It seems that the APP sensor is not the cause for that code

A word of advice . . . make sure the shop that replaces the coolant flow control valve has the proper equipment to replace coolant on a hybrid vehicle

You need to use a machine that can suck out the old coolant, and suck in the new coolant under a vacuum, thus eliminating air pockets.

@Idahogo, like db4690 above says, your fault code doesn’t have anything to do with the accelerator pedal or electronic throttle system. It’s for a coolant control valve. There is a service bulletin out for this and an updated replacement part from Toyota that is required to repair this fault. I believe the cost should be in the $300-$350 range.

Any previous work or recall you had performed related to the pedal isn’t relevant here.

@db4690, I have had mixed results with an AirLift coolant vacuum fill, I rarely use it anymore. For the Prius I open all the bleeder valves, put the gas engine in service mode so it stays running and operate the water pumps to bleed the system. But yes, whoever does this work needs to be familiar with the system.


Thanks for the advice

Thanks for all the feedback. I got the code definition from a link on my OBDwiz software, . This website says the Toyota code is the APP sensor.

Obviously the Toyota Service Bulletin is a better source. I’ll rethink where to go from here and appreciate the correction.