SOLVED! - SEE BELOW


Hi all. My 4runner is stuck in limp mode and I can't figure out why.

ISSUE
P0121, P0123, and P2125 error codes show on my scangauge and immediately reappear after I try to clear them. I have a 2006 V8.

BACKSTORY
I changed the spark plugs on my V8, and in order to do so, I had to remove my intake. While it was removed, I decided to clean my throttle body, which I've done before with no issues. I disconnected the electronic clip and the locking clip snapped. I bought a new clip, re-pinned the wires in the correct order, and that was that. I unbolted the throttle body and cleaned it with the coolant hoses still connected. No issues there.

Throttle body was reinstalled, electronic clip plugged back in, and intake reinstalled. I turned on my car and saw the "VSC OFF" and "VSC TRAC" lights on along with the three error codes on my scangauge. I press on my gas pedal and nothing...f*ck

I've never had an issue with my 4runner. It's gassed up and the gas cap is tight. Disconnecting the battery does nothing. I've searched a number of boards regarding this issue, but there doesn't seem to be a specific fix.

PLEASE chime in if you've experienced this and have a solid fix. Thanks!

P2135: accelerator pedal position sensor fault. There are two of these sensors on the gas pedal that report to the PCM. This data drives the throttle plate motor based on pedal position. When the PCM detects a fault in the pedal sensors the vehicle will enter into limp mode. If you press the pedal and nothing happens that could mean one or both of the sensors are bad or the circuitry is bad. Same thing for the throttle position sensors. That code is thrown because the PCM isn't getting data within the proper thresholds. Could be a bad sensor or circuitry there also. These PCM inputs are critical for the skid control ECU which is why it's been disabled and you see all the lights. So this is when you test your sensors and circuits to locate where the problem lies. You'll need to understand the circuits and sensor values. You'll be checking for continuity between sensors and PCM. You'll be checking for sensor output values, and resistance. You'll be checking the connectors. Might want to make sure you repinned that connector correctly also. Enjoy 🙏

Firstly, I suggest checking if the throttle body is doing its job right. Take a look at the throttle plate and see if there's any weird stuff going on like sticking or blockage. If something's off here, it might be causing those error codes.

Next, pay attention to the throttle position sensor (TPS) and accelerator pedal position sensor (APPS). Check the voltage and resistance readings and make sure they match what the manufacturer recommends. If there's a deviation, it could mean one of these sensors is acting up.

Considering the recent tinkering you did, it's a good idea to double-check the electronic throttle control system calibration. Some cars need a bit of a recalibration after you've done some work. Look up your vehicle's service manual for the lowdown on how to get that system back in sync.

Thank you, I really appreciate the responses.

My local independent Toyota mechanic looked over everything:

- Throttle body and sensors checked OK. I just replaced it with a brand new OEM prior to this new post, and still ran into the same code.
- Throttle body wiring and circuits (voltage) checked OK (I re-pinned everything one by one, so no mistakes there)
- The accelorator pedal sensor and circuits checked OK
- The 4runner runs idle at about 1k. When I press the gas pedal it'll max out at 2k.

He stated what you guys mentioned that the throttle position sensor and accelerator pedal sensor are out of phase correlation, and recommended I take the 4runner to a dealer to reprogram and calibrate the engine idle control system


I'm not familiar with this step and was wondering if anyone knew if it's something the dealership can do, and how much I can expect to shell out for this procedure.

Thanks!

Yes, according to the fsm the learning value reset and idle learning procedures are supposed to be done after replacing or disconnecting most major PCM inputs or cleaning throttle amongst many others. Did your Toyota guy have techstream.. The fsm says it can only be done through techstream but there is a manual way you can do on your own. I do this manual method evertime I do any type of PCM maintenance and throttle body cleaning. The PCM should relearn on it's own after driving enough times. You should try the manual relearn method and might be able to avoid the dealership if everything regarding the sensors and circuits are good. My memory is bad on the procedure but you should be able to locate it online.

I'll check on it later if you can't locate it. Time to burn one down and chill 👌

I found the manual version online that included turning the car on and off twice, starting the car, then placing it in driver for 5+ mins. This unfortunately did not fix anything.

I just swung by another independent Toyota specialist and gave him the rundown. He had never seen the issue before and suggested I replace the throttle body, which I told him I did. He advised he would basically run the same tests to see what's going on, but it's really just a guessing game at this point.

I'm super frustrated, but there really isn't much I can do right now. I'll continue to post updates whenver something is worth mentioning.

Yeah, that's typical mechanic behavior. I'm surprised he didn't say to replace the PCM too. That's what they all say when they can't figure it out. I understand your frustration since it's probably a simple free fix most likely. Did they plug in a scan tool and read live data. A good scanner should tell you if the truck is in limp mode or not. And monitor TPS input and output signal to PCM. Have you observed the throttle body plate while someone is in the truck depressing the pedal. There is something you can do about it now though if you desire. All you need is a multimeter. I would pull the codes manually. There may be other trouble codes the mechanic ignored and could be good clues to the source of the problem. Then use the multimeter to find the issue. All this can be done at home for free. That's not correct PCM relearn procedure I don't think.

This is debatable. You need a good troubleshooter and many mechanics are not. Maybe mention where you are located to see if someone knows of a good guy in your area.

Right, since the mechanic can't read instructions on how to fix this out of a service manual they might get lost and confused when intelligence and knowledge is needed. This is more of an engineering type of problem. Diagnostic technician/mechanic is what you need maybe. They find the actual problem first then fix the problem on the first attempt. They might charge more but that's better than wasting money and time several times. Run engine to operating temperature, turn off all accessories, -turn key to on but don't start position, turn key to off, turn key on but don't start position, turn key off, start truck, engage emergency brake, put truck in drive. You can tell usually if it's relearning. The idle will jump around and start getting back to normal which can take five or ten minutes it varies. After it has smoothed out and back to normal idle in the drive position you can shift through all the other positions also and let idle in each position including neutral and park for about the same amount of time. You need to clear all the trouble codes first though for it to work. That can be done manually also.

USER ERROR

"I disconnected the electronic clip and the locking clip snapped. I bought a new clip, re-pinned the wires in the correct order"

That was my problem. There are TWO red wires (which can look the same when dirty) and I swapped them by accident. They were placed in the correct order, codes were cleared, and the CEL immediately went away on startup. 4runner is back to normal, thank goodness.

For future reference, the order of wires from top down when connected to the throttle body should be:

Yellow
Faded red/Textured red
Red and Black
White
Shiny Red
Green

Again, I appreciate the feedback from all of those that replied, thanks again!

Nicely done!! 🙏