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 higher than the normal operating range of the sensor, the P1120 will set.

Symptoms

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

P1120 CHEVROLET 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).

CHEVROLET Technical Service Bulletins for P1120 code