P0128 on a 2024 Honda Cr V

P0128 means the engine warmed up slower than expected or stayed cooler than the computer expected.

Not your vehicle? See general P0128 info.

Most common causes on the 2024 Honda Cr V

Ranked from 370 NHTSA owner complaints filed for this vehicle.

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1
Head gasket failure causing coolant loss / intrusion
High severity
Multiple owners suffered a catastrophic head-gasket failure with severe coolant loss; the resulting low coolant volume and abnormal flow can prevent the system from reaching or holding the thermostat regulating temperature.
Reported in 3 NHTSA complaints
Parts:head gasket
2
Coolant loss / overheating condition
High severity
One vehicle displayed an 'Engine Hot' warning together with coolant loss, indicating a cooling-system fault severe enough to disrupt normal thermostat-regulated warm-up/temperature control.
Reported in 1 NHTSA complaint
Parts:coolant
3
Stuck-open thermostat
Medium severity
The classic cause of this code — coolant circulates too early, so the sensor never reads a fully warmed engine.
Common cause
Parts:thermostat
4
Failed or drifting ECT sensor
Low severity
A sensor reading falsely low triggers this code even with a normally functioning thermostat.
Common cause
Parts:ECT sensor
5
Cooling fan stuck running / relay fault
Low severity
A fan that won't shut off continues pulling heat from the coolant, delaying warm-up.
Common cause
Parts:cooling fan relay

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These causes are aggregated from NHTSA owner complaints and general repair knowledge — this is not a diagnosis. P0128 on your car still needs shop confirmation before any repair.

Common symptoms

Check engine light
Weak cabin heat
Poor fuel economy
Temperature gauge low
Long warm-up time

What to check before replacing parts

Check coolant level when the engine is cold

Look for: Low coolant reduces the system's ability to reach and hold operating temperature — top off and recheck before assuming the thermostat or sensor is at fault.

Compare scan-tool coolant temperature to actual warm-up time

Look for: An engine that takes noticeably longer than normal to reach operating temperature (or never gets there) on the scan tool, with normal coolant level, points to the thermostat rather than the sensor.

Inspect thermostat operation

Look for: A thermostat stuck open (or opening at the wrong temperature) lets coolant circulate through the radiator too early, keeping the engine running cooler than it should — this is the most common cause of this code.

Check cooling fan command

Look for: A fan that runs constantly or turns on too early (commanded on when temperature is still low) keeps the engine from warming up normally, mimicking a stuck-open thermostat.

Inspect coolant temperature sensor data

Look for: A sensor reading that doesn't rise smoothly with actual engine warm-up, or that reads implausibly low compared to how the engine feels/behaves, points to a sensor or wiring fault rather than a true cooling problem.

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