p0128
Easy Fix
Honda · SUVs
Coolant Thermostat Below Regulating Temperature
Quick Answer
Error code P0128 on your Honda SUVs means: Coolant Thermostat Below Regulating Temperature. This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
RW1RW3RW5RV1CR-V EX 2024CR-V EX-L 2024CR-V Hybrid Sport 2024CR-V Hybrid Sport Touring 2024CR-V Hybrid Sport-L 2024CR-V LX 2024CR-V Sport 2024CR-V Sport Touring 2024HR-V EX-L 2024HR-V LX 2024HR-V Sport 2024Passport EX-L 2024Passport Sport 2024Passport Touring 2024Passport TrailSport 2024Pilot EX 2024Pilot EX-L 2024Pilot Elite 2024Pilot LX 2024Pilot Touring 2024Pilot TrailSport 2024YG7YA7ZD1RZ1
Likely Causes
How to Fix It
1
Allow the engine to fully warm up and monitor coolant temperature with a scan tool; it should reach 190-210 degrees F within a reasonable time
2
Check coolant level in both the reservoir and radiator when cold; top off and bleed air if low
3
Test the ECT sensor resistance at known temperatures and compare to Honda specification chart
4
Remove the thermostat and test in heated water to verify opening temperature (typically 170-180 degrees F)
5
Replace the thermostat and housing gasket if it opens early or fails to close fully
Pro Tip
This is a common issue that most users can resolve without specialized tools. Try the first step before moving on to more complex solutions.
Parts You May Need
Thermostat
Thermostat housing gasket or O-ring
Engine coolant (Honda Type 2 blue)
ECT sensor (if faulty)
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