Powertrain, generic · Fuel and air metering (injector circuit)

P026F Coolant Thermostat Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P026F is a general functional code for the coolant thermostat. CARB requires that the coolant reaches the temperature needed for other diagnostics in the approved time and comes within 11 °C of the thermostat's regulating temperature; from model years 2019–2021 petrol engines must also detect it dropping back below that temperature, and electric pumps or valves controlling coolant flow are monitored like a thermostat. The module follows coolant temperature against a heat model. No manufacturer using P026F was found – GM and Ford report thermostat faults as P0128, P01F0 or P2181 – so the description rests on CARB and the thermostat's function.

Likely causes

Thermostat stuck open or opening too early
Thermostat stuck closed or opening too late
Map-controlled thermostat: heating element or control faulty
Coolant temperature sensor inaccurate
Low coolant or air in the system

Symptoms

  • Check engine light on
  • Slow warm-up, weak heating (stuck open)
  • Low or fluctuating temperature gauge
  • Overheating (stuck closed)

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

P0128P01F0P0125P0126P2181P0116

References: law.cornell.edu, en.wikipedia.org.