P0120 (29) - Throttle Position Signal Circuit

Name of Code:
P0120 (29) - Throttle Position Signal

When Monitored:
Whenever the engine is running.

Set Condition:
This code is set if the throttle angle goes out of range or if throttle angle changes abruptly (i.e.: faster than the throttle body motion could occur)

Theory of Operation:
The Transmission Control Module (TCM) receives the throttle position signal from the Throttle Position Sensor (TPS). The TPS has a 5-volt pull up supplied from the Powertrain Control Module (PCM). The signal is checked for out-of-range as well as intermittency (excessive signal changes).

Transmission Effects:
The MIL will illuminate, the transmission system will not go into limp-in mode. The TCM will use a "calculated throttle angle" supplied by the PCM over the communication bus. If the communication bus is unavailable, the TCM will use a default throttle angle of 24 degrees for the key start in which the code was set. The TCM will try to use the TPS signal again on the next key start. The vehicle may experience extremely erratic transmission shifting just prior to setting the code. If the intermittency does not last long enough to set the code, the customer will say that the transmission violently hunts between gears.

Possible Causes:
- Open or shorted TPS signal and/or ground circuits
- TCM connector problems
- TPS or TPS connector (Check PCM DTC's)
- PCM
- TCM