If the cooling system is not leaking and the fluid level is OK, replacing the thermostat usually takes care of the problem.
Check the 'Possible Causes' listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.
The cost to diagnose the P0128 Cadillac code is 1.0 hour of labor. The diagnosis time and labor rates at auto repair shops vary depending on the location, make and model of the vehicle, and even the engine type. Most auto repair shops charge between $75 and $150 per hour.
The Engine Control Module (ECM) monitors the temperature of the engine coolant for engine control and as enabling criteria for some diagnostics. The amount of heat an engine generates is proportional to the amount of air that enters the engine. The ECM monitors this amount of air to calculate a theoretical Engine Coolant Temperature (ECT). The ECM uses the calculated temperature to determine if the engine has warmed up to the thermostat regulating temperature. Suppose the measured actual coolant temperature does not increase typically or does not reach the thermostat regulating temperature. In that case, diagnostics that use the ECT as enabling criteria, may not run when expected. If the measured engine coolant temperature fails to reach the thermostat regulating temperature, before a predetermined amount of air has entered the engine, this Diagnostic Trouble Code (DTC) sets.
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