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Home >> Pontiac >> 2001 >> Aztek Base, AWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics >> Diagnostic Tests >> DTC P0128: Engine Coolant Fails To Reach Preset Target Temperature >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check, go to next step.
  2. Check coolant level. If coolant level is low, diagnose and repair cause of coolant loss. If coolant level is okay, go to next step.
  3. Turn ignition off. Disconnect ECT sensor harness connector. Connect a fused jumper wire between ECT sensor harness connector terminals. Turn ignition on, with engine off. Using scan tool, observe ECT sensor temperature. If ECT sensor temperature is greater than 280°F (138°C), go to step  7. If ECT sensor temperature is not greater than 280°F (138°C), go to next step.
  4. Turn ignition off. Connect jumper wire between ECT sensor harness connector terminal "B" (Yellow wire) and a known-good ground. Turn ignition on, with engine off. Using scan tool, observe ECT sensor temperature. If ECT sensor temperature is greater than 280°F (138°C), go to next step. If ECT temperature is not greater than 280°F (138°C), go to step  6.
  5. Repair high resistance or open circuit in Orange/Black wire between ECT harness connector terminal "A" and PCM harness connector C1 terminal No. 13. See Figure. After repairs, go to step  10.
  6. Turn ignition off. Repair high resistance or open in Yellow wire between ECT harness connector terminal "B" and PCM harness connector C2 terminal No. 26. After repairs, go to step  10.
  7. Turn ignition off. Remove ECT sensor. Suspend ECT sensor and thermometer in a pan of water. Place pan on a burner or hot plate. Check ECT sensor resistance through the specified range of temperatures. See ENGINE SENSORS & SWITCHES in appropriate SYSTEM & COMPONENT TESTING article. If resistance and temperature closely matches the specified range, go to next step. If resistance and temperature does not closely match the specified range, go to step  9.
  8. Reinstall ECT sensor. Diagnose and repair engine cooling system.
  9. Replace ECT sensor. After replacing sensor, go to next step.
  10. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running this DTC. See CODE ENABLE CRITERIA . If DTC runs and passes, go to next step. If DTC resets, go to step  2.
  11. Using scan tool, observe stored information and CAPTURED INFO. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no DTCs are displayed, system is okay.
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