P0128 Fault Code

Coolant Thermostat (Coolant Temp Below Thermostat Regulating Temperature)

• What does that mean?
• Symptoms
• Causes
• Solutions

The P0128 code indicates that the engine control module (ECM) has detected that the engine coolant temperature is below the thermostat regulating temperature. This can prevent the engine from reaching optimal operating temperature, affecting fuel efficiency and emissions.

What are the symptoms of the P0128 code?

• Engine running cooler than normal, indicated by the temperature gauge
• Check Engine Light illuminated
• Decreased fuel efficiency
• Poor engine performance
• Potential for increased emissions due to incomplete combustion

What causes the P0128 code?

• Faulty thermostat that is stuck open
• Low coolant level causing inaccurate readings
• Faulty temperature sensor or wiring issues
• Engine coolant leaks
• ECM software glitches

How to fix P0128?

• Inspect and test the thermostat for proper operation; replace if faulty.
• Check the coolant level and refill if low; repair any leaks found.
• Inspect the coolant temperature sensor and its wiring for damage.
• Update or reprogram the ECM if necessary.
• Clear the code and perform a test drive to ensure the issue is resolved.