P0128 on a 2016 Chevrolet Colorado

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 2016 Chevrolet Colorado

Ranked from 695 NHTSA owner complaints filed for this vehicle.

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1
Stuck-open thermostat
High severity
A dealer directly diagnosed code P00B7 (coolant flow restriction) with a stuck thermostat on this truck and replaced the thermostat with a coolant flush as the fix -- the textbook root cause of P0128.
Reported in 1 NHTSA complaint
Parts:thermostat
2
Failed engine coolant temperature (ECT) sensor
Medium severity
The same truck later needed its temperature sensor replaced after showing a critical cold-start overheat reading -- a failing ECT sensor reports incorrect coolant temperature and can trigger or mask a P0128 condition.
Reported in 1 NHTSA complaint
Parts:coolant temperature sensor
3
Low coolant level from an external leak
Medium severity
An owner traced a persistent antifreeze odor (with no visible puddling) to a slow external coolant loss requiring repeated top-offs -- insufficient coolant volume delays reaching operating temperature.
Reported in 1 NHTSA complaint
4
Cooling fan stuck running
Low severity
A fan that won't shut off continuously pulls heat out of the engine, delaying warm-up enough to trip the code.
Common cause
Parts:cooling fan relay
5
Thermostat housing or gasket leak
Low severity
A seeping housing gasket slowly drops coolant level and introduces air into the system, both delaying warm-up.
Common cause
Parts:thermostat housing gasket
6
Corroded or damaged ECT sensor wiring/connector
Low severity
A corroded connector can cause an intermittent or falsely low temperature signal that mimics a stuck-open thermostat.
Common cause

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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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