Help! Throttle position sensor error

PeteB

GT40s Supporter
So I'm 100 miles from home at a car show . 7 miles from the show the check engine light comes on and no response to the throttle. Reads code 1238. I let it sit for a while and tried restarting the engine. No check engine light, throttle works fine. I'm a bit concerned about driving all the way tomorrow.
 
Have you had any heat issues?

"""
The primary reason why this part fails is due to exposure to high heat, as it's typically located on the floorboard next to the firewall of the vehicle, in very close proximity to the engine. """
 

Randy V

Admin
Lifetime Supporter
In my experience, TPS are susceptible to carbon tracking which can many times be temporarily cleaned up by simply exercising the TPS through its full range of motion (engine off of course) a dozen times or so.
I'm dating myself, but maybe some of you remember the scratchy volume knob on the radio or stereo system? If you exercised the knob quickly - it would perform adequately for a while.. Same thing - same issue - actually the very same ancient technology..
Will it act up again? Probably. You just exercise it and reboot the ECU and you're on your way. Be aware though, that you could be feeding somewhat dirty signals to the ECU. There is generally fiter circuitry that does a remedial "cleanup" of the signal - so it's not quite as hairy as it would seem...
 

Ken Roberts

Supporter
Is your charging system working good Pete? The ECM watches the voltage of the tps/app circuit carefully and will set a code if the charging system starts to go bad.

Are you sure the code is 1238? I don't see a listing for it. 2138 is a common code for the accelerator pedal position sensor.
 
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PeteB

GT40s Supporter
The code is 2138. Charging system seems fine, showing ~14.5v with the engine running.

Happened again this morning, so I called a friend with a trailer for a rescue. Got it home now, but not really sure what to replace. I guess I'll start with replacing the electronic throttle pedal assembly.
 

Ken Roberts

Supporter
Did you use an extension harness to get the wiring to reach the pedal assembly or did you just unravel the harness and pull out the existing wiring to make it reach. The code has to do with the two sensors in the pedal assembly (voltage reading between the two sensors not matching within parameters). It's either the pedal assembly or the wiring of it back to the ECM.
 
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The code is 2138. Charging system seems fine, showing ~14.5v with the engine running.

Happened again this morning, so I called a friend with a trailer for a rescue. Got it home now, but not really sure what to replace. I guess I'll start with replacing the electronic throttle pedal assembly.
Likely only 3 things:
throttle pedal or throttle body.

if you used a wiring harness extension or did a DIY wiring harness wiring lengthening that could cause it

also, if your tuner played with the throttle body vs pedal positioning in the ecu your ecu might need to be replaced (playing with that area of the ecu can damage or brick the ecu, and it usually doesn't happen right away)
 

PeteB

GT40s Supporter
I didn't extend the harness.

Ordered a new throttle pedal assembly, should be here by Wed. Don't understand why a brand new one only lasted 1200 miles. :huh:
 

PeteB

GT40s Supporter
Did exercising it through full cycles do any good at all?
I took the intake tube off and pushed the throttle plate back and forth a few times, but there's no way to exercise the throttle plate without the engine running with an electronic throttle.
 
I didn't extend the harness.

Ordered a new throttle pedal assembly, should be here by Wed. Don't understand why a brand new one only lasted 1200 miles. :huh:
it can also be the throttle body - you need to make sure the style of tb (gold vs silver .... late vs early model) is matched to how your ECU is programmed (and you can't change this).

it's also possible there's an issue with the wiring harness - with one of the GMPP wiring harness I bought the pedal would work for 2 or 3 minutes after the ecu was on, then just stop working. Replaced the whole wiring harness and no more issues (and the wiring harness before that one had no pedal issues, so clearly wiring harness issue). I imagine this issue would have showed up much earlier on, but maybe something isn't soldered/connected good enough and worked its way loose.
 

Randy V

Admin
Lifetime Supporter
it can also be the throttle body - you need to make sure the style of tb (gold vs silver .... late vs early model) is matched to how your ECU is programmed (and you can't change this).

it's also possible there's an issue with the wiring harness - with one of the GMPP wiring harness I bought the pedal would work for 2 or 3 minutes after the ecu was on, then just stop working. Replaced the whole wiring harness and no more issues (and the wiring harness before that one had no pedal issues, so clearly wiring harness issue). I imagine this issue would have showed up much earlier on, but maybe something isn't soldered/connected good enough and worked its way loose.
I had forgotten about this....
We actually had it happen to a 2010 Camaro SS / LS3 that we gutted for a racecar back in 2009-10.. Opting to save weight and time we installed the GM Performance Parts wiring harness. Doggoned thing stopped responding to pedal input and set a code. We would reset the codes and it would work again for a few mins.
As it turned out, we had to replace the Throttle Body with the GMPP unit before the system worked together. That was a bitter pill to swallow because at that time, the TB was something like $450!
 
I had forgotten about this....
We actually had it happen to a 2010 Camaro SS / LS3 that we gutted for a racecar back in 2009-10.. Opting to save weight and time we installed the GM Performance Parts wiring harness. Doggoned thing stopped responding to pedal input and set a code. We would reset the codes and it would work again for a few mins.
As it turned out, we had to replace the Throttle Body with the GMPP unit before the system worked together. That was a bitter pill to swallow because at that time, the TB was something like $450!
yea, there's 2 style of LS throttle bodies - early and late model - they look almost the same (one is gold throttle plate, one is silver), same electrical connector, but they open in reverse of eachother and the dbw doesn't like if the ecu is mis-matched to the throttle body
 

PeteB

GT40s Supporter
Installed a new gas pedal. No codes and seems to be working. Hopefully this solves the problem :huh::uneasy:
 

PeteB

GT40s Supporter
Well, happened again today, so it wasn't the pedal. Cycled the ignition and the pedal worked again, although the check engine light is still on.

Does Chevy Performance have a tech support number?
 
replace the throttle body. make sure you match it to the style your ecu is hard-programmed for (either gold or silver .... silver is early-LS style, gold is later/newer-LS style)
 

Ken Roberts

Supporter
The gold blade throttle bodies are made by Hitachi and can be bought through other channels. Hitachi makes them for GM and puts GM on their castings. You can save a bundle and just buy the "non GM" branded T bodies from Hitachi as part number #ETB0026. They can be bought new as low as $135. The GM part number for the 2009 and up gold blade throttle bodies is #12605109. They usually sell for $200 and up.
 
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