Diagnostic Aids
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The following conditions can also set the DTC:
- DTC P0128 occurring with insufficient vehicle interior heating is an indication of improper thermostat operation.
- Corrosion on the engine coolant temperature (ECT) sensor terminals or the engine coolant temperature (ECT) sensor harness connector results in a greater voltage on the engine coolant temperature (ECT) sensor signal circuit, which is interpreted by the ECM as a colder engine coolant temperature (ECT) sensor.
- A slight to moderate resistance in the engine coolant temperature (ECT) sensor signal circuit or low reference circuit will affect this diagnostic. This condition results in a greater voltage on the engine coolant temperature (ECT) sensor signal circuit, which is interpreted by the ECM as a colder engine coolant temperature (ECT) sensor.