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Home >> Suzuki >> 2003 >> XL-7 Base, RWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0128: Coolant Thermostat Malfunction >> Diagnosis & Repair Procedure
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Diagnosis & Repair Procedure

  1. If engine system check has been performed, go to next step. If engine system check has not been performed, go to A4: ENGINE SYSTEM CHECK  under SYSTEM TESTS.
  2. Check thermostat operation. Thermostat should begin to open at 175.4-182.6°F (79.7-83.7°C). Thermostat should be completely open at 203°F (95°C). Thermostat valve should lift to more than 5/16" (8 mm). If problem is found, replace thermostat as necessary. After repair, repeat DTC CONFIRMATION TEST . If no problem is found, go to next step.
  3. Turn ignition off. Disconnect ECT sensor 3-pin harness connector. ECT sensor is located at front of intake manifold. Use a fused jumper wire, connect ECT sensor harness connector terminals No. 1 (Orange/Black wire) and No. 3 (Gray/Yellow wire). Turn ignition on. Observe ENGINE COOLANT TEMPERATURE parameter displayed on scan tool. If parameter is 327°F (164°C), go to step  5. If parameter is not as specified, check for open or short in Orange/Black wire between ECT sensor and ECM. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Also, check for open or short in and Gray/Yellow wire between ECT sensor and ECM. If problem is found, repair as necessary. After repair, repeat DTC CONFIRMATION TEST . If no problem is found, go to next step.
  4. Substitute a known-good ECM, and repeat DTC CONFIRMATION TEST . If DTC does not reset, testing is complete.
  5. Check ECT sensor operation. See ENGINE COOLANT TEMPERATURE SENSOR under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING article. If problem is found, replace as necessary. After repair, repeat DTC CONFIRMATION TEST . If no problem is found, go to next step.
  6. Substitute a known-good ECM, and repeat DTC CONFIRMATION TEST . If DTC does not reset, testing is complete.
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