DTC P1221: Excessive Difference Between Throttle Position Sensors: Description

WARNING: This page does not describe the selected car, but rather 11 other vehicles, including the 2002 GMC Yukon XL, 2002 GMC Yukon, 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, and 2002 Chevrolet Tahoe. However, it is still accessible from the selected car via links, so may be relevant.

The Throttle Position (TP) sensor is mounted on the throttle body assembly. The sensor is actually 2 individual TP sensors within 1 housing. Two separate signal, low-reference and 5-volt reference circuits are used to connect the TP sensor assembly to the Throttle Actuator Control (TAC) module. The 2 sensors have opposite functionality. TP sensor 1 and Accelerator Pedal Position (APP) sensor 1 share a 5-volt reference circuit that are connected within the TAC module. TP sensor 2 and APP sensor 2 share a 5-volt reference circuit that are connected within the TAC module. If an out of range condition is detected with the TP sensor 2, this DTC will set and the Reduced Engine Power message will be displayed. The THROTTLE POSITION SENSOR POSITION table shows the percentage and voltage readings of the scan tool based on the position of the TP. See THROTTLE POSITION SENSOR POSITION table under DTC P1220: THROTTLE POSITION SENSOR 2 - VOLTAGE OUT OF RANGE.