Test Description
The numbers below refer to the step numbers on the diagnostic table.
- 3: This step tests for excessive resistance in the ECT circuit.
- 4: This step tests for a skewed sensor through the range of temperatures that affects this DTC.
DTC P0128
| Step | Action | Values | Yes | No |
|---|---|---|---|---|
| Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module 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 | Is the engine cooling system low on coolant? | - | Go to Loss of Coolant | Go to Step 3 |
| 3 | Is the customer's concern that the engine does not reach operating temperature or that the heater output is low? | - | Go to Thermostat Diagnosis (LY7) | Go to Step 4 |
| 4 |
CAUTION:
Refer to Road Test Caution
.
|
10°C (18°F) | Go to Step 6 | Go to Step 5 |
| 5 |
|
- | Go to Step 6 | Go to Diagnostic Aids |
| 6 |
IMPORTANT:
Return to this diagnostic procedure after you complete the thermostat diagnosis. Test for the correct operation of the thermostat. Refer to Thermostat Diagnosis (LY7)
.Did you find and correct the condition? |
- | Go to Step 15 | Go to Step 7 |
| 7 |
|
139°C (282°F) | Go to Step 11 | Go to Step 8 |
| 8 |
|
139°C (282°F) | Go to Step 9 | Go to Step 10 |
| 9 | Test the low reference circuit of the ECT sensor for high resistance. Refer to Circuit Testing
and Wiring Repairs
. Did you find and correct the condition? |
- | Go to Step 15 | Go to Step 12 |
| 10 | Test the signal circuit of the ECT sensor for high resistance. Refer to Circuit Testing
and Wiring Repairs
. Did you find and correct the condition? |
- | Go to Step 15 | Go to Step 12 |
| 11 | Test for shorted terminals and poor connections at the ECT sensor. Refer to Testing for Intermittent Conditions and Poor Connections
and Connector Repairs
. Did you find and correct the condition? |
- | Go to Step 15 | Go to Step 13 |
| 12 | Test for shorted terminals and poor connections at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections
and Connector Repairs
. Did you find and correct the condition? |
- | Go to Step 15 | Go to Step 14 |
| 13 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement
. Did you complete the replacement? |
- | Go to Step 15 | - |
| 14 | Replace the ECM. Refer to Control Module References
for replacement, setup, and programming. Did you complete the replacement? |
- | Go to Step 15 | - |
| 15 |
|
- | Go to Step 2 | Go to Step 16 |
| 16 | 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 |