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Home >> Mazda >> 2003 >> Tribute LX, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 61 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P0126 & DTC P0128 >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2003 Mazda Protege5 and 2003 Mazda Protege. However, it is still accessible from the selected car via links, so may be relevant.
  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 next step.
  2. Inspect For Other DTCs -  Ensure no other DTCs have been set at this time. If any other DTC has been set, repair that problem first. Refer to DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no other DTCs are set, go to next step.
  3. Verify Coolant Thermostat Operation -  Turn off A/C and all electrical loads. Remove cooling fan relay No. 1 located in main fuse block at left side of engine compartment. Using scan tool, monitor ECT PID. Warm up engine until ECT PID reads 210°F (99°C). Connect fused jumper wire between cooling fan relay No. 1 harness connector terminals "A" (battery power) and "B" (cooling fan) to operate cooling fan. ECT PID data should indicate a continuous decrease that stops at 176-183°F (80-84°C), thermostat is closed. If ECT PID data does not decrease as specified, remove jumper wire and go to next step. If ECT PID data decreases as specified, remove jumper wire and go to step  5.
  4. Inspect Coolant Thermostat For Whether Stuck Open -  Remove coolant thermostat and verify thermostat is not stuck open. If thermostat is stuck open, replace coolant thermostat. After repair, go to next step. If thermostat is okay, check Engine Coolant Temperature (ECT) sensor operation. See ENGINE COOLANT TEMPERATURE SENSOR under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. Replace ECT sensor if necessary. Go to next step.
    NOTE: If workshop interior and outdoor temperature difference is significant, PCM might not operate thermostat monitor. In order for PCM to operate thermostat monitor, manufacturer recommends allowing engine to cool with vehicle outside workshop.
  5. Verify Monitoring Condition For Repair Verification -  Reconnect all connections. Allow engine to cool. Turn ignition on, engine off. Clear DTCs. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Access ECT and IAT PIDs. Ensure PID values are within specification. IAT PID data should be more than 14°F (-10°C). Difference between ECT and IAT PIDs should be less than 6°C. If all PID data is as specified, for DTC P0126 go to next step or for DTC P0128 go to step  7. If any PID is out of specification, cool down engine and repeat this step.
    NOTE: This step requires actual driving of vehicle. DO NOT use chassis roller for this test. Allow engine to cool with vehicle outside workshop. Test drive must be performed with no more than 3 stops within a 5 minute drive period. Test period depends on engine coolant temperature at engine start. The warmer the engine coolant, the less time required for test. For example: If engine coolant temperature is 14°F (-10°C), monitoring period is 38 minutes, but if engine coolant temperature is 86°F (30°C) monitoring period is 8 minutes.
  6. Verify Trouble Shooting Of DTC P0126 Completed -  Start engine. Turn off A/C and all electrical accessories. Using scan tool, access DIAGNOSIS MONITORING TEST RESULTS in GENERIC OBD II FUNCTIONS. Monitor TEST #10:32:00. Drive vehicle 25-62 MPH until TEST value changes. If measured value is more than minimum value, go to step  8. If measured value is less than minimum value, replace PCM. For PCM removal and installation, see POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION article. After repair, go to step  8.
  7. Verify Trouble Shooting Of DTC P0128 Completed -  Start engine. Turn off A/C and all electrical accessories. Using scan tool, access DIAGNOSIS MONITORING TEST RESULTS in GENERIC OBD II FUNCTIONS. Monitor TEST #10:30:00 or #10:31:00. Drive vehicle at 25-62 MPH until TEST value is changed. If measured value is more than maximum value, 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 measured value is less than maximum value, go to next step.
  8. 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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