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Home >> Mazda >> 2002 >> Tribute LX, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 59 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P0121: Throttle Position Sensor Stuck Closed/Open >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2003 Mazda MPV and 2002 Mazda MPV. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ensure freeze frame data has been recorded and go to next step.
  2. Verify Related Pending Code Or Stored DTC -  Turn ignition on, engine off. Using scan tool, retrieve DTCs. If DTC P0101 is not present, go to next step. If DTC P0101 is also present, diagnose and repair first. See DTC P0101: MASS AIRFLOW SENSOR INCONSISTENT WITH THROTTLE POSITION SENSOR .
  3. Verify Related Repair Information Availability -  Check for service bulletins and on-line information. Repair as necessary according to available information. If vehicle is not repaired, go to next step. If related repair information is not available, go to next step.
  4. Verify Current Input Signal Status - Is Concern Intermittent Or Constant -  Start engine. Access ECT, TP and MAF PIDs. Warm up engine until ECT PID is more than 158°F (70°C). Drive vehicle. Read TP PID while MAF PID is more than 88.3 gram/sec. If TP PID is more than 12.5 percent, go to step  7. If TP PID is not as specified, go to next step.
  5. Verify TP PID -  Start engine. Access TP, MAF and RPM PIDs. Read TP PID while MAF PID is less than 5.3 gram/sec. and RPM PID is more than 500 RPM. If TP PID reading is more than 50 percent, go to step  12. If TP PID is not as specified, go to next step.
  6. Verify Current Input Signal Status - Is Concern Intermittent Or Constant -  Drive vehicle and read MAF PID. If MAF PID value changes with driving condition, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article. If MAF PID value does not change with driving conditions, check MAF sensor and related circuits. See MASS AIRFLOW SENSOR under SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - MAZDA6. MIATA, MPV, PROTEGE & PROTEGE5 article. After repair, go to step  11.
  7. Check TP Sensor Terminals For Electrical Corrosion -  Turn ignition off. Disconnect TP sensor 3-pin harness connector. Check for electrical corrosion on terminals. If no problem is found, go to next step. If electrical corrosion is found, repair or replace corroded terminals or replace TP sensor. After repair, go to step  11.
  8. Verify TP Sensor -  Verify operation of TP sensor. Measure resistance between terminals "A" and "B". If resistance changes smoothly while gradually opening throttle valve, go to next step. If TP sensor does not operate as specified, replace TP sensor. After repair, go to step  11.
  9. Check PCM Terminals For Electrical Corrosion -  Disconnect PCM 104-pin harness connector. Check for electrical corrosion on terminals. If no problem is found, go to next step. If corrosion is found, repair as necessary. After repair, go to step  11.
  10. Check Constant Voltage Supply & TP Signal Circuits For Voltage Drop -  Connect 104-pin Breakout Box (49-UN01-130) to PCM harness connector only. See Figure. Turn ignition on, engine off. Measure voltage between following terminals:
    • TP sensor 3-pin harness connector terminal "C" (Brown/White wire) and breakout box terminal No. 90.
    • TP sensor 3-pin harness connector terminal "B" (Gray/White wire) and breakout box terminal No. 89.

    If voltage reading is about zero volts, disconnect breakout box and go to next step. If voltage reading is not as specified, check for rust or corrosion at PCM 104-pin harness connector terminals No. 89 and 90. Repair as necessary. After repair, remove breakout box and go to next step.

  11. Verify Trouble Shooting Of DTC P0121 Completed -  Reconnect all connectors. Turn ignition on, engine off. Using scan tool, clear DTC from memory. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Start engine. Access ECT, TP and MAF PIDs. Warm up engine until ECT PID is more than 158°F (70°C). Drive vehicle and read TP and MAF PIDs. Ensure MAF PID is more than 88.3 gram/sec. and TP PID is more than 12.5 percent for more than 5 seconds. If DTC P0121 is present, replace PCM. After repair, go to step  17. If DTC P0121 is not present, go to step  17.
  12. Check TP Sensor Terminals For Electrical Corrosion -  Turn ignition off. Disconnect TP sensor 3-pin harness connector. Check for electrical corrosion at connector terminals. If no problem is found, go to next step. If corrosion is found, repair corroded terminals or replace TP sensor. After repair, go to step  16.
  13. Check Ground Circuit For Voltage Drop -  Check resistance between ground and TP sensor 3-pin harness connector terminal "A" (Orange wire). If resistance reading is about zero ohms, go to next step. If resistance reading is not as specified, repair or replace PCM 104-pin harness connector terminal No. 91 (Brown/Yellow wire). After repair, go to step  16.
  14. Verify TP Sensor Operation -  Measure resistance at TP sensor. If resistance reading changes smoothly while gradually opening throttle valve, go to next step. If TP sensor reading does not change as specified, replace TP sensor. After repair, go to step 16.
  15. Check PCM Terminals For Electrical Corrosion -  Disconnect PCM 104-pin harness connector. Check for electrical corrosion at connector terminals. If no problem is found, go to next step. If corrosion is found, repair corroded terminals as necessary. After repair, go to next step.
  16. Verify Trouble Shooting Of DTC P0121 Completed -  Reconnect all connectors. Turn ignition on, engine off. Using scan tool, clear DTC from memory. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Start engine. Access RPM, TP and MAF PIDs. Ensure TP PID reading is less than 50 percent while MAF PID is less than 8.25 gram/sec. and RPM PID is more than 500 RPM. If DTC P0121 is present, replace PCM. After repair, go to next step. If DTC P0121 is not present, go to next step.
  17. Verify After Repair Procedure -  Using scan tool, perform After Repair Procedure. See AFTER REPAIR PROCEDURE . If no other DTCs are present, testing is complete. If any other DTC is present, go to applicable test and repair.
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