SES Light Due to DTC P0128 - keywords cold SES thermostat

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Some customers may comment, of a SES/MIL telltale illuminated, with DTC P0128 recorded.

The DTC P0128 sets when the actual engine coolant temperature does not reach minimum normal operating temperature threshold temperature at a specific time. The PCM counter does not reach 75°C (167°F) by a predetermined time.

Refer to SI Document ID # 1453214. However, Warranty part returns and root cause analysis confirms that the ECT sensor is NOT an effective corrective action. Root cause analysis indicates the component responsible for DTC P0128 is the engine thermostat.

For a DTC P0128, replace the thermostat and return original thermostat for additional analysis.

Please ship Engine Thermostat assembly to the following address:

Warranty Parts Center (WPC)

45 Northpointe Drive

Orion, Mi 48359

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.