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Technical Electronic Throttle Control issue


New member
Apr 1, 2023
I have a single-owner, bone-stock, garage-kept, dealer-maintained 2018 124 Spider Lusso with about 22k miles.

In fall of 2022, while stopped at a red light, the car shuddered like it was going to stall and the radio re-set. The check engine light came on and the Electronic Throttle Control (ETC) light started blinking. I was ten minutes from home so I continued to drive. The longer I drove, the less responsive the accelerator pedal became. I got home and researched the issue. Some people said that they simply restarted the vehicle and the ETC problem never happened again.

Any time I drive the car for more than about 20 minutes, at some point the ETC light will start blinking. If I keep driving, the accelerator pedal becomes less and less responsive. If I pull over and re-start the car, the ETC light turns off and the accelerator pedal works normally. Sometimes the check engine light stays on after the re-start, sometimes it re-sets also.

I took the car to an oil change shop and they read the error code: P2138 "Accelerator Pedal position, sensor 1/2 correlation". I researched and found that the accelerator pedal has two potentiometers which measure the position of the pedal and if the signal from both of them does not agree, it throws an error code.

I took the car to the Fiat dealer and they said they fixed it. I drove twenty minutes and the problem came back.

I took the car back to the Fiat dealer and they said they fixed it. I drove five minutes and the problem came back.

I did more research and thought the problem might be the battery; the battery is original. I took it to two different auto zones and they ran their tests, and it tested “good”.

Since the error code indicated a problem with the accelerator pedal sensors, I swapped out the pedal and sensor unit myself (Mazda part N245-41600-B). I drove it for about fifteen minutes and the ETC error began flashing again.

I took the car to a Mazda dealer and they said they were not capable of diagnosing the problem.

Any ideas? Thanks in advance.