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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 103 (Engine Controls Self-Diagnostics - 2.2L) >> Diagnostic Tests >> DTC P0128: Engine Coolant Thermostat >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Pontiac Sunfire, 2002 Pontiac Grand Am, 2002 Oldsmobile Alero, and 2002 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
  2. If cooling system is low on coolant, repair cooling system as necessary. If cooling system is not low on coolant, go to next step.
  3. Turn ignition off. Disconnect ECT sensor. Connect fused jumper wire (3-amp) between ECT sensor connector terminals. Turn ignition on, engine off. Using scan tool, observe ECT sensor temperature. If scan tool indicates ECT sensor temperature is more than 280°F (138°C), go to step  7. If scan tool does not indicate ECT sensor temperature is more than 280°F (138°C), go to next step.
  4. Turn ignition off. Connect a 3-amp fused jumper wire between the signal circuit of the ECT sensor and a known-good ground. Turn ignition on, with engine off. With a scan tool, observe the ECT sensor temperature. Does the scan tool indicate that the ECT sensor temperature is more than 280°F (138°C)? If yes, go to next step. If no, go to step  6.
  5. Test the ECT sensor low reference circuit for a high resistance or an open. Repair circuit as necessary. Did you find and correct the condition? If yes, go to step  10. If no, go to DIAGNOSTIC AIDS .
  6. Test the ECT sensor signal circuit for a high resistance or for an open. Repair circuit as necessary. Did you find and correct the condition? If yes, go to step  10. If no, go to DIAGNOSTIC AIDS .
  7. Remove the ECT sensor. Suspend the ECT sensor and a thermometer in a pan of water. Place the pan on a burner or hot plate. Test the resistance of the ECT sensor through the specified range of 50-194°F (10-90°C). Does the resistance and temperature closely match the Temperature vs Resistance table? See TEMPERATURE VS RESISTANCE  table. If yes, go to next step. If no, go to step  9.
  8. Reinstall ECT sensor. Diagnose engine for not reaching operating temperature.
  9. Replace ECT sensor. When complete, go to next step.
  10. Clear the DTCs with a scan tool. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running the DTC. See CONDITIONS FOR RUNNING DTC . Does the DTC run and pass? If yes, go to next step. If no, DIAGNOSTIC AIDS .
  11. Using scan tool, observe stored information. Does scan tool display any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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