Honda P0128-Cooling System Malfunction

Honda P0128 – Cooling System Malfunction

Code P0128 Honda cooling system malfunction is DTC code for coolant thermostat malfunction. P0128 code generate when engine control module (ECM) detects that engine has not reached the expected temperature within a specified time after starting. This code indicate an issue with engine cooling component.

Fault Location – Engine cooling system.

Possible Causes Code P0128 Honda

Thermostat stuck open or not functioning properly, leak in engine coolant system, clogged radiator or malfunction radiator fan, water pump failing, vacuum or other air leak in engine causing incorrect air/fuel mixture, faulty temperature sensor, relay or other electrical component preventing engine control module (ECM) to detect accurate engine temperature.

Honda P0128 DTC Code Possible Symptoms

Engine takes longer to heat-up, decreased fuel efficiency, heating system may not provide consistent warm air to cabin, engine reduce power or may run poorly, engine check light illuminates.

How To Fix Code P0128

1.Check for coolant level verify that there are no leaks in coolant system.

2.Inspect water pump if found faulty replace it with new one.

3.Inspect thermostat if found stuck open it should be replace with new thermostat.

4.Clean radiator if found clogged. On some instance replaced radiator.

5.Repair air leaks if found, air leaks should be repaired to put back engine to normal performance.

6.Inspect temperature sensor if found faulty replace it with new one.

7.Inspect for electrical issues perform a diagnostic test to identify and repair the problem.


Its important to have the vehicle inspected and diagnosed by professional mechanic to find and resolve issue associated with p0128 for proper repair.

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