The powertrain control module (PCM) has an internal table that looks at the manifold absolute pressure (MAP) sensor values with respect to the throttle position (TP) sensor values. If the throttle position sensor indicates the engine is near wide open throttle (WOT) but the MAP sensor reading indicates the high vacuum reading, decel or idle, this DTC will set.

DTC P0121 will set if the tp sensor vs. the MAP sensor relationship is not consistant with normal engine operation, a low MAP reading and a high TP reading when:

Important: The TP signal range is continuously checked when the following conditions have been met.

DTC P0121 indicates that either the TP sensor or MAP sensor is skewed outside its normal operating range.

Check the TP sensor and MAP sensor connectors for corrosion.

Check the PCM connector for corrosion.

Move the throttle and check the TP sensor voltage readngs on the scan tool. If the throttle moves without a change in TP sensor voltage the TP sensor return spring may be sticking. If this condition occurs, replace the TP sensor.

At a closed throttle position, the out put of the TP sensor is low, approximately 0.4 volts. as the throttle plate opens, the output increases so that, at WOT, the output voltage should be approximately 4.9 volts.

When attempting to diagnose an intermittent problem, use the scan tool to review the malfunction history information. This data cabn be used to duplicate a problem.

Check the tightness of the female terminal grip with a spare male terminal.

An intermittent open in circuit 452 will cause a DTC P0121.