DTC P0128: Coolant Thermostat Malfunction: Condition
WARNING: This page is about a different car, the 2002 Suzuki Esteem. However, it is still accessible from the selected car via links, so may be relevant.
DTC is set when difference in engine coolant temperature between ECT sensor No. 1 and ECT sensor No. 2 is too small. Engine coolant temperature circuit is monitored once per drive cycle. MIL is illuminated when Engine Control Module (ECM) detects malfunction during 2 consecutive drive cycles. Possible causes are:
- Thermostat malfunction.
- ECM malfunction.