Code 21: TPS Signal Volt High: Notes

WARNING: This page is about a different car, the 1990 Pontiac Firebird and 1990 Chevrolet Camaro. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Test numbers refer to test numbers on diagnostic chart.

Code 21 will set if TPS is greater than 4.5 volts with ignition on or if the engine is running, TPS voltage is high, airflow is low and all 3 conditions have existed for 3-10 seconds. This step confirms Code 21 is present.
With TPS sensor disconnected, the TPS voltage should go low if the ECM and wiring are okay.
Probing the ground circuit with a test light to battery voltage checks the 5-volt return circuit. A faulty 5-volt return will cause a Code 21.