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DTC P0121: TP Sensor Circuit Range/Performance Problem

NOTE: DTC is set when Throttle Position (TP) sensor signal is out of range or performance is poor. For connector terminal wire colors, see appropriate wiring diagram in WIRING DIAGRAMS article. For component locations, see appropriate illustration under COMPONENT LOCATIONS in SELF-DIAGNOSTICS - INTRODUCTION article.
NOTE: Before replacing any component, ensure all connectors at component and ECM are clean and tight. After making any repairs, disconnect ECM harness connector for 10 seconds, connect ECM harness connector and retest system. It is necessary to generate an ECM readiness code if ECM memory is cleared, battery voltage is disconnected or ECM is disconnected. Engine Control Module (ECM) and Throttle Valve Control Module (TVCM) must also be matched when either component is replaced or when TVCM is removed and reinstalled.
  1. Turn ignition off. Disconnect Throttle Valve Control Module (TVCM) harness connector. Turn ignition on. Measure voltage between terminals No. 4 and 7 at TVCM harness connector. See Figure. Voltage should be about 5 volts. Measure voltage between terminals No. 3 and 7 at TVCM harness connector. Voltage should be about 10 volts. If voltages are not as specified, go to next step. If voltages are as specified, go to step  3.
  2. Turn ignition off. Disconnect Engine Control Module (ECM) harness connector. Connect Test Box (VAG 1598/18) to ECM harness connector, but not to ECM. Measure resistance between terminal No. 3 at TVCM harness connector and socket No. 10 at test box. Measure resistance between terminal No. 4 at TVCM harness connector and socket No. 41 at test box. Measure resistance between terminal No. 7 at TVCM harness connector and socket No. 33 at test box. All resistances should be less than 1.5 ohms. If resistances are as specified, replace ECM. If any resistance is not as specified, repair open in appropriate circuit between TVCM and ECM.
  3. Turn ignition off. Connect TVCM harness connector. Disconnect Engine Control Module (ECM) harness connector. Connect Test Box (VAG 1598/18) to ECM harness connector, but not to ECM. Measure resistance between sockets No. 10 and 33 at test box with fully closed throttle and fully open throttle (WOT). Resistance should be infinite with fully open throttle and 10 ohms or less with fully closed throttle. Measure resistance between terminals No. 27 and 53 at test box with fully closed throttle. Resistance should be 2-300 ohms. If resistances are as specified, go to step  5. If resistance is not as specified, go to next step.
  4. Disconnect TVCM harness connector. Measure resistance between terminal No. 1 at TVCM harness connector and socket No. 27 at test box. Measure resistance between terminal No. 2 at TVCM harness connector and socket No. 53 at test box. Measure resistance between terminal No. 5 at TVCM harness connector and socket No. 40 at test box. Measure resistance between terminal No. 8 at TVCM harness connector and socket No. 62 at test box. All resistances should be less than 1.5 ohms. If any resistance is not as specified, repair open in wiring between TVCM and ECM. If all resistances are as specified, go to next step.
  5. Disconnect TVCM harness connector. Measure resistance between sockets No. 10, 27, 33, 40, 41, 53, and 62 at test box. All resistances should be infinite between each circuit. If any resistance is not as specified, repair circuits shorted to each other between TVCM and ECM. If all resistances are as specified, go to next step.
  6. Replace TVCM with known-good unit. Clear DTCs. Test drive vehicle and recheck for DTCs. If DTC P0121 resets, go to next step. If DTC P0121 does not reset, replace TVCM.
  7. Turn ignition off. Disconnect MAF sensor harness connector. Measure resistance between terminal No. 1 at MAF sensor harness connector and socket No. 1 at test box. See Figure. Resistance should be less than 1.5 ohms. If resistance is not as specified, repair open in wiring between MAF sensor and ECM. If resistance is as specified, go to next step.
  8. Using a fused jumper wire, connect terminals No. 1 and 2 at MAF sensor harness connector. Measure resistance between sockets No. 1 and 16 at test box. Resistance should be less than 1.5 ohms. If resistance is as specified, remove jumper wire and go to next step. If resistance is not as specified, repair open in wiring between MAF sensor and ECM.
  9. Using a fused jumper wire, connect terminals No. 1 and 4 at MAF sensor harness connector. Measure resistance between sockets No. 1 and 17 at test box. Resistance should be less than 1.5 ohms. If resistance is as specified, remove jumper wire and go to next step. If resistance is not as specified, repair open in wiring between MAF sensor and ECM.
  10. Measure resistance between sockets No. 16 and 17 at test box. Resistance should be infinite. If resistance is as specified, replace ECM. If resistance is not as specified, repair circuits shorted to each other between MAF sensor and ECM.
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