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Home >> Mazda >> 2003 >> Protege5 Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0121: Throttle Position Sensor Circuit - Range/Performance Problem >> Diagnostic Procedure

Diagnostic Procedure

  1. Verify Related Repair Information Availability -  Turn ignition off. Connect scan tool to DLC-2. Turn ignition on, engine off. Monitor for FREEZE FRAME DATA and ensure data has been recorded. Check service bulletins for repair information related to this DTC. If repair information is not available, go to next step. If repair information is available, perform diagnosis and repair as necessary. After repair, go to step  11.
  2. Verify Related Pending Code & Stored DTC -  Turn ignition off, then start engine. Using scan tool, check for DTCs. If DTC P0101 is not present, go to next step. If DTC P0101 is also present, diagnose and repair as necessary. See DTC P0101: MASS AIRFLOW SENSOR CIRCUIT RANGE/PERFORMANCE PROBLEM .
  3. Verify Related Repair Information Availability -  Check service bulletins for repair information related to this DTC. If repair information is not available, go to next step. If repair information is available, perform diagnosis and repair as necessary. After repair, go to next step.
  4. Verify Current Input Signal Status - Is Concern Intermittent Or Constant -  Start engine. Using scan tool, access ECT, RPM 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 73.4 grams/sec. (137.4 grams/sec. if equipped with traction control). If TP PID reading is more than 12.5 percent, go to next step. If TP PID reading is not as specified, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES article.
  5. Verify TP PID -  Using scan tool, clear DTCs. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Access TP, MAF and RPM PIDs. Start engine. Read TP PID while MAF PID is less than 4.8 grams/sec. and RPM PID is more than 500 RPM. If TP PID reading is more than 50 percent, go to step  7. If TP PID reading 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 reading changes with driving condition, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article. If MAF PID reading does not change as specified, check MAF sensor and related circuits and terminals. See MASS AIRFLOW SENSOR under ENGINE SENSORS & SWITCHES in SYSTEM AND COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. Repair or replace as necessary. After repair, go to step  11.
  7. Check TP Sensor Terminals For Electrical Corrosion -  Turn ignition off. Disconnect TP sensor 3-pin harness connector. Inspect TP sensor harness connector terminals (male and female). If no problems are found, go to next step. If problem is found, repair as necessary. After repair, go to step  11.
  8. Check Ground Circuit For Voltage Drop -  Measure resistance between ground and TP sensor harness connector terminal "B" (Orange wire). See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. If resistance reading is about zero ohms, go to next step. If resistance is not as specified, repair or replace corroded PCM 104-pin harness connector terminal No. 91 (Orange wire). After repair, go to step  11.
  9. Verify TP Sensor Operation -  Check operation of TP sensor. If TP sensor resistance changes smoothly while slowly opening throttle valve, go to next step. If TP sensor does not operate as specified, replace TP sensor. After repair, go to step  11.
  10. Check PCM Terminals For Electrical Corrosion -  Disconnect PCM 104-pin harness connector. Check for corrosion at PCM harness connector terminals No. 89 (Brown/Yellow wire), 90 (Pink/Black wire) and 91 (Orange wire). If corrosion is not found, go to next step. If any corrosion is found, repair or replace terminal(s) as necessary. After repair, go to next step.
  11. Verify Trouble Shooting Of DTC P0121 Completed -  Reconnect all connectors. Turn ignition on, engine off. Clear DTCs. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Start engine. Access RPM, ECT, TP and MAF PIDs. Check following:
    • Verify TP PID reading is less than 50 percent while MAF PID is less than 5 grams/sec. and RPM PID is more than 500 RPM.
    • Warm up engine until ECT PID reading is 158°F (70°C).
    • Drive vehicle and read TP and MAF PIDs. Verify MAF PID reading is more than 73.4 grams/sec. and TP PID is more than 12.5 percent for more than 5 seconds.

    If DTC P0121 is present, replace PCM. For PCM removal and installation, see POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION article. After repair, go to next step. If same DTC P0121 is not present, go to next step.

  12. 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, follow appropriate DTC diagnostic procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
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