P1221 GMC Possible Causes
- Faulty throttle position sensor (TP)
- Throttle position sensor (TP) harness is open or shorted
- Poor electrical connection in the throttle position sensor (TP) circuit
How to Fix GMC Code P1221?
Start by checking the “possible causes” listed above. Visually inspect the corresponding wiring harness and connectors. Look for damaged components and check for broken, bent, pushed out, or corroded connector pins.
Possible Symptoms
- Engine light on (or engine service warning light soon)
P1221 GMC Meaning
The throttle position sensor (TP) is mounted on the throttle body of the throttle actuator control (TAC) assembly. The sensor is actually 2 individual throttle position sensors in 1 housing. Two separate signal circuits, one low reference circuit and one 5-volt reference circuit are used to connect the TP sensor assembly and the TAC module. The TP sensor signal voltage increases as the throttle opens. The TP sensor signal circuit is pulled up to a 5-volt reference voltage.