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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 P0126 & DTC P0128: Thermostat Stuck 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. Record freeze frame data. Check for service bulletins and on-line information. Repair as necessary. After repair, go to next step.
  2. Inspect For Other DTCS -  Check for any other DTCs. If no other DTCs are present, go to next step. If any other DTCs are present, diagnose and repair first.
  3. Inspect Coolant Thermostat For Whether Stuck Open -  Perform coolant thermostat inspection. Visually inspect and ensure thermostat is not stuck open. Thermostat should start to open at 183-190°F (84-88°C) and be fully open at 210°F (99°C). If thermostat is not stuck open and operates as specified, go to next step. If thermostat operation is not as specified, replace coolant thermostat. After repair, go to next step.
    NOTE: For next step, if working inside and outside temperature difference is significant, PCM might not operate thermostat monitor. Therefore, it is recommended to cool down engine outside of workshop.
  4. Verify Monitoring Condition For Repair Verification -  Reconnect all components. Allow engine to cool down. Turn ignition on, engine off. Using scan tool, clear DTC. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Access ECT and IAT PIDs. Ensure ECT PID is less than 88°F (31°C), IAT PID is 14°F (-10°C) and difference between ECT and IAT PIDs is less than 43°F (6°C). If any PIDs are not as specified, cool down engine and repeat this step. If PIDs are as specified, go to next step for DTC P0126 or go to step  6 for DTC P0128.
  5. Verify Trouble Shooting Of DTC P0126 Completed -  Start engine. Turn off A/C and all electrical loads. Using scan tool, access DIAGNOSTIC MONITORING TEST RESULTS and monitor TEST #10:32:00.
    NOTE:
    • This test requires actual driving. (Chassis roller cannot be used).
    • During test drive, constant speed should be maintained, although 2 or 3 stops during every 5 minutes of driving time (traffic signals) is acceptable. Stop and go driving is not acceptable (traffic congestion).
    • Test period depends on ECT at engine start up. (If ECT is 14°F (-10°C), monitoring period is 38 minutes. If ECT is 86°F (30°C), monitoring period is 8 minutes.)

    Verify TEST 10:32:00 value. If value is more than minimum value, go to step  7. If value is more than minimum value, replace PCM. After repair, go to step  7.

  6. Verify Trouble Shooting Of DTC P0128 Completed -  Start engine. Turn off A/C and all electrical loads. Using scan tool, access DIAGNOSTIC MONITORING TEST RESULTS and monitor TEST #10:31:00 or #10:32:00.
    NOTE:
    • This test requires actual driving. (Chassis roller cannot be used).
    • During test drive, constant speed should be maintained, although 2 or 3 stops during every 5 minutes of driving time (traffic signals) is acceptable. Stop and go driving is not acceptable (traffic congestion).

    Verify TEST 10:31:00 or 10:32:00 value. If value is less than maximum value, go next step. If value is not less than maximum value, replace PCM. After repair, go next step.

  7. 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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