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Home >> Subaru >> 2002 >> Forester Base >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Controls - Self-Diagnostics - 2.5L >> Diagnostic Tests >> DTC P0122: Throttle Position (TP) Sensor Circuit Low Input

DTC P0122: Throttle Position (TP) Sensor Circuit Low Input

  1. Perform test procedure. See TESTING PROCEDURE . Start engine. Using a scan tool, monitor Throttle Position (TP) sensor signal. If TP sensor signal value is less than 0.1 volt, go to next step. If TP sensor signal value is not less than 0.1 volt, circuit has returned to normal. Check for intermittent conditions. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES  and VERIFICATION PROCEDURE  .
  2. Using a DVOM, measure voltage by backprobing between 30-pin ECM electrical harness connector B136 terminal No. 15 (Red wire on Forester; Light Blue wire on Impreza and Outback Sport; Red/Black wire on Legacy and Outback) and good chassis ground point with throttle valve fully closed. See Figure. If voltage is more than 4.5 volts, go to step  4. If voltage is not more than 4.5 volts, go to next step.
  3. Using a DVOM, measure voltage by backprobing between 30-pin ECM electrical harness connector B136 terminal No. 15 (Red wire on Forester; Light Blue wire on Impreza and Outback Sport; Red/Black wire on Legacy and Outback) and good chassis ground point while wiggling ECM harness and connector. See Figure. If voltage changes more than 4.5 volts, repair poor terminal contact in ECM connector. If voltage does not change more than 4.5 volts, contact authorized Subaru dealership because probable cause is deterioration of multiple parts. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES  and VERIFICATION PROCEDURE  .
  4. Using a DVOM, measure voltage by backprobing between 30-pin ECM electrical harness connector B136 terminal No. 17 (Light Green wire on Forester, Impreza and Outback Sport; White/Black wire on Legacy and Outback) and good chassis ground point. See Figure. If voltage is less than 0.1 volt, go to step  6. If voltage is not less than 0.1 volt, go to next step.
  5. Using a DVOM, measure voltage by backprobing between 30-pin ECM electrical harness connector B136 terminal No. 17 (Light Green wire on Forester, Impreza and Outback Sport; White/Black wire on Legacy and Outback) and good chassis ground point while wiggling ECM harness and connector. See Figure. If voltage does not change more than 0.1 volt, go to next step. If voltage changes more than 0.1 volt, repair poor terminal contact in ECM connector. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES  and VERIFICATION PROCEDURE  .
  6. Turn ignition off. Disconnect 4-pin electrical harness connector from TP sensor. Turn ignition on. Using a DVOM, measure voltage between TP sensor 4-pin electrical harness connector terminal No. 4 (Red wire on Forester, Legacy and Outback; Yellow/Red wire on Impreza and Outback Sport) and good engine ground point. See Figure. If voltage is more than 4.5 volts, go to next step. If voltage is not more than 4.5 volts, locate and repair open circuit in wiring between ECM and TP sensor. Also check for poor contact in all connectors between TP sensor and ECM. See ENGINE PERFORMANCE in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES  and VERIFICATION PROCEDURE  .
  7. Turn ignition off. Using a DVOM, measure resistance between 30-pin ECM electrical harness connector B136 terminal No. 17 (Light Green wire on Forester, Impreza and Outback Sport; White/Black wire on Legacy and Outback) and TP sensor 4-pin electrical harness connector terminal No. 3 (White/Black wire on Forester; White/Red wire on Impreza and Outback Sport; White wire on Legacy and Outback). See Figure and Figure . If resistance is less than one ohm, go to next step. If resistance is not less than one ohm, locate and repair open circuit in wiring between ECM and TP sensor. Also check for poor contact in all connectors between TP sensor and ECM. See ENGINE PERFORMANCE in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES  and VERIFICATION PROCEDURE  .
  8. Using a DVOM, measure resistance between TP sensor 4-pin electrical harness connector terminal No. 3 (White/Black wire on Forester; White/Red wire on Impreza and Outback Sport; White wire on Legacy and Outback) and good engine ground point. See Figure. If resistance is more than one megohm, go to next step. If resistance is not more than one megohm, locate and repair short to ground in wiring between ECM and TP sensor. See ENGINE PERFORMANCE in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES  and VERIFICATION PROCEDURE  .
  9. Check for poor terminal contact in TP sensor electrical harness connector. Repair TP sensor connector as necessary. If connector is okay, replace TP sensor. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES  and VERIFICATION PROCEDURE  .
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