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Home >> Suzuki >> 2001 >> XL-7 Limited >> Repair and Diagnosis >> External Pages >> Different car >> Section 59 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P0128: Coolant Thermostat Malfunction >> Diagnosis & Repair Procedure

Diagnosis & Repair Procedure

WARNING: This page is about a different car, the 2003 Suzuki XL-7. However, it is still accessible from the selected car via links, so may be relevant.
  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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