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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 83 (Engine Controls Self-Diagnostics - 2.2L) >> Diagnostic Tests >> DTC P0128: Engine Coolant Fails To Reach Preset Target Temperature >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 GMC Sonoma and 2002 Chevrolet S10 Pickup. 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, go to next step.
  2. Is the cooling system low on coolant? If yes, check and repair cause of loss of coolant. If no, go to next step.
  3. Turn ignition off. Disconnect the ECT sensor connector. Connect a 3-amp fused jumper wire between the signal circuit and the low reference circuit of the ECT sensor. Turn ignition on, with engine off. Observe the ECT sensor temperature with a scan tool. Does the scan tool indicate that the ECT sensor temperature is greater than 280°F (138°C)? If yes, go to step  7. If no, 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. Observe the ECT sensor temperature with a scan tool. Does the scan tool indicate that the ECT sensor temperature is greater than 280°F (138°C)? If yes, go to next step. If no, go to step  6.
  5. Test the ECT sensor reference low circuit for a high resistance or an open. Repair the circuit as necessary. Did you find and correct the condition? If yes, go to step  10. If no, see DIAGNOSTIC AIDS .
  6. Test the ECT sensor signal circuit for a high resistance or an open. Repair the circuit as necessary. Did you find and correct the condition? If yes, go to step  10. If no, see 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 appropriate SENSOR OPERATING RANGE CHARTS article. If yes, go to next step. If no, go to step  9.
  8. Reinstall ECT sensor. After installing sensor, diagnose engine for failing to reach normal operating temperature.
  9. Replace ECT sensor. After replacing sensor, 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, go to step  2.
  11. Observe the stored information in Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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