What does the P0128 code mean?

P0128 means the engine is not reaching its normal operating temperature in the expected amount of time. The computer watches coolant temperature against airflow and run time - if the engine warms up too slowly, it sets this code. The usual cause is a thermostat stuck open, letting coolant circulate before the engine is warm. It rarely affects drivability but hurts fuel economy and heater performance.

What are the most common causes of P0128?

The most common causes are: Thermostat stuck open (most common); Low coolant level; Faulty engine coolant temperature (ECT) sensor; Cooling fan running when it should not; Wrong (too-cold) thermostat previously installed.

Is it safe to drive with a P0128 code?

Usually yes - P0128 rarely changes how the car drives. Still fix it, because it keeps the check-engine light on and will fail an emissions test.

How much does it cost to fix P0128?

Typical US independent-shop repair cost for P0128 runs about $150 - $400, depending on the root cause. Common fixes: Replace the thermostat; Top up and bleed the coolant; Replace the ECT sensor if it reads incorrectly.

P0128 Code: Coolant Temperature Below Thermostat Regulating Temperature - Meaning, Causes & Fix Cost

P0128: Coolant Temperature Below Thermostat Regulating Temperature