Conditions for Clearing the MIL/DTC
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2004 Oldsmobile Bravada, 2004 GMC Envoy XUV, 2004 GMC Envoy XL, 2004 GMC Envoy, and 2004 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
- 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: Powertrain Control Module (PCM) Connector End Views or Engine Controls Connector End Views |
||||
| 1 | Did you perform the Diagnostic System Check-Engine Controls? | - | Go to Step 2 | Go to Diagnostic System Check - Engine Controls |
| 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 (LL8) or Draining and Filling Cooling System (LM4) in Engine Cooling | Go to Step 3 |
| 3 | Test and verify the proper operation of the thermostat. Refer to Thermostat Diagnosis
in Engine Cooling. Did you find and correct the condition? |
- | Go to Step 14 | Go to Step 4 |
| 4 |
|
- | Go to Step 14 | Go to Step 5 |
| 5 | Measure the voltage from the signal circuit of the ECT sensor to a good ground with a DMM. Refer to Circuit Testing
in Wiring Systems. Is the voltage within the specified range? |
4.8-5.2 V | Go to Step 6 | Go to Step 8 |
| 6 | Measure the voltage from the signal circuit of the ECT sensor to the low reference circuit of the ECT sensor with a DMM. Is the voltage within the specified range? |
4.8-5.2 V | Go to Step 9 | Go to Step 7 |
| 7 | Test the ECT sensor low reference circuit for high resistance. Refer to Circuit Testing
and Wiring Repairs
in Wiring Systems. Did you find and correct the condition? |
- | Go to Step 14 | Go to Step 11 |
| 8 | Test the ECT sensor signal circuit for high resistance. Refer to Circuit Testing
and Wiring Repairs
in Wiring Systems. Did you find and correct the condition? |
- | Go to Step 14 | Go to Step 11 |
| 9 |
|
- | Go to Step 10 | Go to Step 12 |
| 10 | Install the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement
. Is the action complete? |
- | Go to Intermittent Conditions | - |
| 11 | Test for an intermittent and for a poor connection at the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections
and Connector Repairs
in Wiring Systems. Did you find and correct the condition? |
- | Go to Step 14 | Go to Step 13 |
| 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 PCM. Refer to Powertrain Control Module (PCM) Replacement
. Did you complete the replacement? |
- | Go to Step 14 | - |
| 14 |
|
- | 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 | System OK |