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P2138 - Throttle/Pedal Position Sensor/Switch


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I would agree ^^.

My TB was, by my experience, pretty darn clean to begin with. I was not confident that my efforts would do anything, but hey, the issue never returned.

I chalk it up to a very sensitive system. These cars don't have idler veins, so there must always be a slight and consistent gap at full close which some sludge could interfere with.

 

I couldn't see a reasonable way to get that plastic cap off the TB at all, let alone while on th car. How is/was this done by others? Was that shown to help the problem as well? I did not do that as part of my solution, but I did attempt to blast cleaner up through the butterfly pivot.

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I would agree ^^.

My TB was, by my experience, pretty darn clean to begin with. I was not confident that my efforts would do anything, but hey, the issue never returned.

I chalk it up to a very sensitive system. These cars don't have idler veins, so there must always be a slight and consistent gap at full close which some sludge could interfere with.

 

I couldn't see a reasonable way to get that plastic cap off the TB at all, let alone while on th car. How is/was this done by others? Was that shown to help the problem as well? I did not do that as part of my solution, but I did attempt to blast cleaner up through the butterfly pivot.

 

there are metal clips holding the plastic cover on .. its very easy to disassemble

 

in a 2.5 turbo you would probably have to remove the throttlebody to remove the cover.

 

no there are no idle vanes in the throttlebody because it doesnt use a stepper motor or pwm motor. it uses the throttle plate its self for idle control.

 

its default angle when unplugged is slightly open so the car will idle about 1800 rpm so the car can limp home.

 

but again the code refers to a problem between the two sensors with in the throttle body unit where there supposed to be saying the same thing. if there is an argument power is removed from the unit.

 

if the throttle body is not able to close enough it sets a different code i think its excessive idle speed. p2109

Edited by frank_ster

Now that's thinking out of the boxer!:lol:

fyi all 05 + legacy's have built in code reader

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  • 6 months later...

hi my name is kenny melancon

I placed a few notes on here about your code issue, I have fixed my car by cleaning the throttle body no replacement of any parts, I can explain the code to you if you wish

, my car has never set the code again. and I have also fixed 4 other cars the same way

Edited by Kenny Melancon
removed my phone number as requested by another person
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  • 1 month later...

can you take the old one apart ? clean it and reinstall it ?

it would help us understand what the root cause.

 

the pedal and throttle body are made in a way they dont wear out.

 

the only thing would be contamination that would make it not work.

Now that's thinking out of the boxer!:lol:

fyi all 05 + legacy's have built in code reader

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  • 5 months later...
Not sure about any vids, but feel free to PM me if you have any questions. I have done this before and it is pretty easy. Start with the intercooler off, then the intake piping to the throttle body. Leave the TB on the car so as to not need to replace gaskets. Hose down in cleaner. Careful not to move the butterfly too much - just hold it open and do what you need to.
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Cleaning the inside of the throttle body may not help anything , this was an issue for carbon on cars with a iac getting stuck.

 

You need to take the plastic cover off the side of the throttle body. If its a non turbo car is very easy . And clean around the magnetic pickup for the throttle position sensor. And put it back together.

 

On turbo car you need to take off the throttle body. The gasket is actually a o ring and they usually dont break.

 

 

The error code is for missmatch between the 3 different sensors in the throttle plate . Basically if all 3 arnt saying the same thing it sets code and outs car into limp mode.

Edited by frank_ster

Now that's thinking out of the boxer!:lol:

fyi all 05 + legacy's have built in code reader

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Update...problem solved!

 

Visited the local Subaru dealer and asked about diagrams/part numbers/ cost of replacement/etc. After talking to a mechanic the guy said he was told I could try to clean the terminals/sensors but usually once the check engine light came on it was time to replace. I was also told about the two 12mm bolts holding the gas pedal in place and the plug connecting everything. Finally, if a replacement was needed it would have been $180 out the door.

 

Came home, unbolted the gas pedal and disconnected the plug. Blew into it...boy was that full of dust!!, then I reconnected everything and started the car....no more check engine light!! Hasn't come back since!

 

Seems like it worked. And if it comes back, I can clean it again or just replace it but I'd find the part online rather than paying $180.

 

Just figured I'd share.

 

Thanks!

 

-Emt1581

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  • 2 months later...

My wife's 2006 2.1i threw this code for the first time today. It went into limp mode 2 blocks from our local Subaru dealer so I took it there. Unfortunately, it is a holiday weekend, so other than reading the code, no-one could look at it until Tuesday (so it is sitting in their shop). I read a little about this, it seems that there are some fixes but most seem to be temporary. I'm not one for typically working on my own vehicle, so I'm pretty sure I'll let the dealership fix for me.

 

I guess my question is, what should I expect them to come back with? Replace the pedal assembly? Or just a sensor? Any idea what I should expect to pay?

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  • 2 months later...

I know this is an old thread, but I've searched many forums and haven't found any with a permanent solution.

 

I've been having this problem on my 2005 Baja Turbo 5MT w/ 72K miles since I bought it in May, but hasn't been a problem with my 2004 Baja Turbo 4EAT w/176K miles that I bought in February. The RPMs would fluctuate to 1500 rpms and below at idle or I could feel small surges in gear just before the CEL would come on. I would notice sometimes that the cruise light would flash before the CEL would illuminate. I don't know if this problem is related to the difference in ECUs and people usually don't post about their trans configuration, so I cannot say for sure. This is just my experience. Seems unusual that the car with 176K miles operates fine and the 72K mile car is plauged with this issue.

 

So far, I've done all the tests in the service manual, more than twice. I haven't done any data logging, but I hooked up my Subaru Select Monitor and both signal outputs seem to be normal when I depress the accelerator through it's full range of motion. I've tried swapping the pedals and have even replaced the pedal with a new Subaru OEM part. Nothing has worked. It has started to become a daily occurence and can be quite dangerous in certain situations. I think it has to do with humidity like others have mentioned, because it usually occurs more on cloudy/rainy days and early in the morning/late in the evening. The P2138 code refers to a difference in the voltage output of the two potentiometers in the pedal assembly. I thought that maybe I'd try hooking both signal inputs going to the ECU to one of the signal outputs on the pedal assembly so that there would never be any differences in voltage, causing the ECU to go into limp mode. It has been three days so far and the idle is much smoother, there are no longer any surges, and I have not yet had a CEL.

 

DISCLAIMER !!!!

 

Try this mod at your own risk, but I think that limp mode is much more dangerous and have had many close situations where I've lost the pedal on a busy highway, crossed dangerous intersections or even stalled out on hills. If you try this mod and you have a surge or wide open throttle situation, just be aware that the simplest thing to do is to put the car in neutral before pulling over and turning off the ignition. I say this as a disclaimer, because this situation happened with the Toyota pedal recalls and people died.

 

Below is a link to pictures of the schematic for the pedal position sensor and my jerry rigged wiring job. I unhooked the connectors and used some other terminals I had from another harness to make my mod reversible without cutting any wires. The signal input wires on my car are the blue with white stripe and the white with blue stripe. They are terminals 2 and 5 on the wiring harness.

 

imgur.com/a/io0Fm

 

I hope this helps. Every forum I've read hasn't found a solution and I've even read about individuals selling their car because of this. I'm too stubborn and I love my Bajas.

 

The wife says I have to sell one though.

 

I will report back if I have any further issues.

Edited by RSdude
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I don't know what cap you're referring to, but I have cleaned both connectors on both the pedal assembly and the throttle body assembly with no results. The last thing I tried was cleaning the throttle body and butterfly valve with carb cleaner. Like most turbos without a catch can, there was a film of oil residue that I thought might be causing the throttle plate to stick. If you try this, be prepared for a temporary episode of white smoke coming out the exhaust.

 

Update

 

My modification is still working with no check engine lights or limp mode conditions. I have noticed random micro surges in the throttle like before, but they no longer result in a check engine light and limp mode. The surges are barely noticeable and don't affect the throttle enough to be a problem or a safety concern. Actually, they are so slight, that they do not affect driveability at all. I noticed that I have my modification hooked up to the Sub-accelerator signal, so maybe if I feel like crawling back down into the firewall cave, I'll try the Main-accelerator signal and see if the micro-surges still occur.

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the cover on the throttle body, it has the sensor in side of the cover which reads the magnetic pickup from the throttle plate .

 

i dont think oil can cause issues with this type of sensors.

Now that's thinking out of the boxer!:lol:

fyi all 05 + legacy's have built in code reader

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My throttle body is a sealed unit. The servo and TPS are not serviceable, but this code does not refer to the throttle body, it refers to the a voltage variation in the two redundant sensors in the accelerator pedal.

 

As stated previously, I have replaced the pedal assembly with no positive results. Many other people have tried replacing the pedal too and it has not corrected the issue.

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From my experence this code is for both the throttlebody and the pedal sensor , as i have a buick engine and stand alone ecu along side of the factory ecu. Wheni probed the wires on the theottle body i could recreate the code everytime .

 

The pedal assembly and the throttle body have magnetic contactless position sensors with inverted curves. One ramping up with poaition and one down . If the sensors dont point to the same position the code is set and lompmode acticated.

 

My throttle body when i remove it has a plastic cover where the plug plugs into. I removed that cover and cleaned the metal bits of the magnetic pickup and that solved my issue.

 

If you even force open the servo with your finger with ignition on it will also set this code.

Now that's thinking out of the boxer!:lol:

fyi all 05 + legacy's have built in code reader

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This thread is regarding Subaru P2138 code with dual contact potentiometers and factory ECU's. The later models have magnetic Hall effect sensors. To avoid confusing other Subaru owners plagued with this issue, I think your comments regarding a Buick with standalone ECU and magnetic Hall effect sensors belong in another forum.
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This thread is regarding Subaru P2138 code with dual contact potentiometers and factory ECU's. The later models have magnetic Hall effect sensors. To avoid confusing other Subaru owners plagued with this issue, I think your comments regarding a Buick with standalone ECU and magnetic Hall effect sensors belong in another forum.

 

buick engine, all subaru sensors, this thread was started with issues with a 05 legacy gt witch is what i have. i only mentioned the buick engine because i have played with the system and had this even triggered a few times because of my doing and after because of metal chips in the stock subaru throttle body unit.

 

so it seems you have an older version of drive by wire. that i have not seen before.

Now that's thinking out of the boxer!:lol:

fyi all 05 + legacy's have built in code reader

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  • 4 months later...
Been a few months....still fine.

 

The airbag light comes and goes which just means I need to work on or replace the overhead light board.

 

Other than that, no issues.

 

-Emt1581

 

Been 6 more months...still fine! :)

 

-Emt1581

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