Conditions for Clearing the MIL/DTC

The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.

DTC P0128

Step	Action	Values	Yes	No
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module (ECM) Connector End Views or Engine Controls Connector End Views
1	Did you perform the Diagnostic System Check - Vehicle?	-	Go to Step 2	Go to Diagnostic System Check - Vehicle
2	IMPORTANT: The cooling fans are commanded ON when certain engine coolant temperature (ECT) DTCs are set. Is the cooling system coolant low?	-	Go to Draining and Filling Cooling System (LS4 Static Fill) or Draining and Filling Cooling System (LZE, LZ4, LZ9 Static Fill) or Draining and Filling Cooling System (9C1, 9C3 Static Fill) or Draining and Filling Cooling System (LS4 GE 47716 Fill) or Draining and Filling Cooling System (LZE, LZ4, LZ9, 9C1, 9C3 GE 4771 Fill)	Go to Step 3
3	Test and verify the proper operation of the thermostat. Refer to Thermostat Diagnosis . Did you find and correct the condition?	-	Go to Step 14	Go to Step 4
4	Disconnect the ECT sensor. Inspect for the following conditions: Corrosion on the ECT sensor terminals Improper or corroded terminals at the ECT harness connector Loose terminals in the ECT harness connector-Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition?	-	Go to Step 14	Go to Step 5
5	Test for an intermittent and for a poor connection at the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition?	-	Go to Step 14	Go to Step 6
6	Measure the resistance of the ECT sensor signal circuit between the sensor and the ECM with a DMM. Refer to Circuit Testing . Is the resistance within the specified range?	0-10 ohm	Go to Step 7	Go to Step 10
7	Measure the resistance of the ECT sensor low reference circuit between the sensor and the ECM with a DMM. Refer to Circuit Testing . Is the resistance within the specified range?	0-10 ohm	Go to Step 8	Go to Step 11
8	Turn OFF the ignition. Remove the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement . Place the sensor on a work surface away from any heat source. Allow the sensor to reach the ambient air temperature for 30-60 minutes. Observe and record the ambient air temperature of the vehicle environment using an accurate thermometer. IMPORTANT: DO NOT hold the ECT sensor by the probe. Measure the resistance of the ECT sensor and record the value. Compare the resistance measurement of the ECT sensor to the ambient air temperature on the Temperature vs. Resistance table. Refer to TEMPERATURE VS RESISTANCE . Is the resistance measurement of the ECT sensor within the specified range?	-	Go to Step 9	Go to Step 12
9	Install the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement . Is the action complete?	-	Go to Step 13	-
10	Repair the high resistance in the ECT sensor signal circuit. Refer to Wiring Repairs . Did you complete the repair?	-	Go to Step 14	-
11	Repair the high resistance in the ECT sensor low reference circuit. Refer to Wiring Repairs . Did you complete the repair?	-	Go to Step 14	-
12	Replace the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement . Did you complete the replacement?	-	Go to Step 14	-
13	Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement?	-	Go to Step 14	-
14	Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition?	-	Go to Step 2	Go to Step 15
15	Observe the Capture Info. with a scan tool. Are there any DTCs that have not been diagnosed?	-	Go to Diagnostic Trouble Code (DTC) List - Vehicle	System OK