DTC P0121: Throttle Position (TP) Sensor System Performance

NOTE: If DTCs P0121, P0122 or P0123 are set together, diagnose DTCs P0122 or P0123 first. See DTC P0122: THROTTLE POSITION (TP) SENSOR CIRCUIT LOW INPUT or DTC P0123: THROTTLE POSITION (TP) SENSOR CIRCUIT HIGH INPUT .

If using scan tool, connect scan tool to Data Link Connector (DLC). Select TP sensor parameter on scan tool. Measure TP sensor output voltage. If using DVOM, measure voltage at PCM connector terminal C51-3-9. See PIN VOLTAGE/CIRCUIT RESISTANCE CHARTS article. With engine off, fully warmed up and throttle closed, voltage should be between .5-1.2 volts. With throttle fully opened, voltage should be between 3.4-4.7 volts. If voltage is as specified, replace PCM and retest system. If voltage is not as specified, go to next step.
Disconnect TP sensor harness connector. Inspect all terminals for corrosion or poor contact. If okay, test TP sensor resistance. See SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING article. If TP sensor resistance is not as specified, replace TP sensor. If resistance is as specified, check for open circuit in Gray/Red, Red/Green or Gray/Yellow wires between TP sensor and PCM. Repair as necessary and retest system.