Possible causes

– Faulty Throttle Position Sensor
– Throttle Position Sensor harness is open or shorted
– Throttle Position Sensor circuit poor electrical connection
– Throttle Position Sensor not properly adjusted

When is the code detected?

When the Powertrain Control Module (PCM) senses a signal voltage lower than the normal operating range of the sensor, the P1121 will set.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P1122 GMC Description

The Throttle Position (TP) sensor is a potentiometer. The TP sensor provides a voltage signal that changes relative to throttle blade angle. This signal voltage is one of the most important inputs used by the Powertrain Control Module (PCM). The TP sensor has a 5.0 volt reference, a ground and a signal circuit.
TP sensor Signal voltage should be about 0.6 volt at idle. The TP sensor voltage should increase to above 4.0 volts at wide open throttle (WOT).