MasterTuning Fault code dictionary (DTC)

P0128 — Engine does not reach operating temperature

Severity: Informational Can you drive? Yes, no known limitation Make: All makes (OBD-II standard)
MeaningThe engine takes too long to warm up, or never reaches the expected temperature. It looks like a detail, but a cold engine uses more fuel, soots up the particulate filter and prevents it from regenerating.
FamilyPowertrain (P)

Typical symptoms

Low temperature gauge reading
Lukewarm cabin heating
Higher fuel consumption
DPF regeneration never starting

Common causes

Thermostat stuck open (most common cause)
Temperature sensor out of calibration
Low coolant level
Cooling fan running constantly

What to do

A thermostat is cheap and quick to replace, and worth doing: an engine that stays cold is the hidden cause of many DPF and fuel consumption problems.

Frequently asked questions

What does code P0128 mean?

Engine does not reach operating temperature. The engine takes too long to warm up, or never reaches the expected temperature. It looks like a detail, but a cold engine uses more fuel, soots up the particulate filter and prevents it from regenerating.

Can I keep driving with code P0128 active?

Yes, no known limitation

Common causes — P0128

Thermostat stuck open (most common cause) Temperature sensor out of calibration Low coolant level Cooling fan running constantly

How do you fix code P0128?

A thermostat is cheap and quick to replace, and worth doing: an engine that stays cold is the hidden cause of many DPF and fuel consumption problems.

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