I have a 2007 Sonata, and recently the ESC light and check engine
light will come on at the same time, and at that point, the car enters
what they call "limp mode". After 3 trips to the dealership, still
no luck. They have replaced the gas pedal, but that does not fix the
problem. Any suggestions? An on-line mechanic suggested the TPS
might be the problem, but I’m not sure if that is related to what was
already replaced. I can’t drive the car any distance as this is very
dangerous when it happens!

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There are a variety of reasons the car can enter limp-home mode, all of
them having to do with the electronic throttle not being able to function
properly. The computer does this to prevent any sort of uncontrolled
acceleration that could lead to losing control of the vehicle.

Presuming the dealer received a code indicating a problem with the
accelerator position sensor, replacing the accelerator pedal assembly,
which contains the sensor, would be the typical repair. Presuming the
same code returns, we've either got a defective or incorrect replacement
part, a problem in the circuit between the pedal and the PCM, or a problem
with the PCM itself.

Typically, when this issue arises, the readings are again correct by the
time the car reaches the dealer, usually reducing the technician to making
an educated guess from the data stored by the PCM.

According to the people I've talked to at Hyundai, the problem is usually
the accelerator pedal assembly (again, presuming a trouble code for the
accelerator position sensor), but they've also seen issues with the
harness connector for the pedal assembly as well as the harness connector
for the PCM.

A last idea that I have stuck in the back of my head is that the
diagnostic tool's description of the trouble codes makes unclear whether
the problem was with the accelerator position sensor (on pedal) readings
or the throttle position sensor (on throttle body) readings. Hyundai has
issued TSBs to clarify this, but there's no guarantee the technican knows
about these or bothered to look. Does any of your paperwork indicate the
trouble codes retrieved from the PCM?

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