DTC P0121 - Throttle Position (TP) Sensor Circuit Performance

Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
Turn ignition on. Observe MAP sensor parameter on scan tool. If display is less than 65 kPa, go to next step. If display is not as specified, go to step 5).
Turn ignition off. Disconnect MAP sensor harness connector. Connect a test light between MAP sensor voltage reference circuit and MAP sensor signal circuit at harness connector. Turn ignition on. If display on scan tool is less than 65 kPa, replace MAP sensor. Retest system. If display is not as specified, go to next step.
Turn ignition off. Using an ohmmeter, check for an open, short to ground or short to MAP sensor ground circuit. Repair as necessary. If wire is okay, replace PCM. Retest system.
Observe TP sensor angle on scan tool while slowly opening throttle. If display shows a steady increase from zero percent to 100 percent, check for an intermittent problem. See TESTS W/O CODES article. If display is not as specified, go to next step.
Turn ignition off. Disconnect TP sensor harness connector. Turn ignition on. Observe TP sensor parameter on scan tool. If display is zero volts, go to next step. If display is not as specified, go to step 8).
Turn ignition off. Connect a test light between voltage reference circuit and sensor signal circuit at TP sensor harness connector. Turn ignition on. If display is 5 volts, replace TP sensor. Retest system. If display is not as specified, go to step 9).
Check for the following items:
- TP sensor signal circuit shorted to power.
- High resistance in TP sensor ground circuit.
Repair as necessary. If no problems are found, replace PCM. Retest system.
Check for the following items:
- Poor connection in TP sensor signal circuit or voltage reference circuit.
- High resistance in TP sensor voltage reference circuit.
Repair as necessary. If no problems are found, replace PCM. Retest system.