Powertrain, generic · Fuel and air metering

P01F0 Coolant Temperature Relapsed Below Diagnostic Monitoring Temperature

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

Since model years 2019–2021 CARB requires petrol engines to detect a thermostat fault not only during warm-up but also when the coolant, after reaching operating temperature, drops back below the temperature needed for other diagnostics. P01F0 is this check. GM sets it when coolant falls below 64 °C with a conventional thermostat or 70.5 °C with an electrically heated one (2019 Corvette: 65/78.5 °C) after having been above it, with at least 0.8 km driven, ambient above −7 °C, enough heat input and no long overrun downhill; two trips. GM also uses it on the 6.6 litre Duramax diesel as a 'stuck open thermostat' check. Ford does not use the code in the documents checked. Usual cause is a thermostat stuck open.

Likely causes

Thermostat stuck open or not sealing
Heated map thermostat, thermal management valve or switchable water pump faulty
Radiator fan running constantly (relay stuck)
Coolant sensor drifting cold
Low coolant or air in the system

Symptoms

  • Check engine light on (after two drive cycles)
  • Temperature gauge drops while driving
  • Weak cabin heating, higher consumption

Repair estimate

DifficultyMediumDIY possible
Parts and labour€60–400
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

thermostatengine coolant temperature sensorcooling system

Related codes

P0128P0125P0116P0597P01E4

References: law.cornell.edu, gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com.