Powertrain, generic · Fuel and air metering

P0125 Insufficient Coolant Temperature for Closed Loop Fuel Control

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

Closed-loop mixture control using the oxygen sensors is only released once the coolant has reached a minimum temperature. CARB requires that this happens within set times – from 2006 two minutes if the engine starts up to 8 °C below the release temperature, five minutes if 8–19 °C below. P0125 means it took too long. Ford checks once per cold start and fails if coolant is still below 10 °C while its model already expects over 27 °C; Mitsubishi expects about 7 °C within 90–300 s and also fails if coolant drops back below 40 °C. Long idling suspends the test. Usual causes are a thermostat stuck open or a sensor reading too cold. GM does not use this code in the tables checked.

Likely causes

Thermostat stuck open (especially in cold weather)
Coolant sensor reading too cold or slow (drift, contact resistance)
Low coolant level or air at the sensor
Much idling or coasting in frost
Engine control module

Symptoms

  • Check engine light on
  • Engine warms up slowly, heater stays cold for a long time
  • Higher consumption during warm-up
  • Temperature gauge reads low

Repair estimate

DifficultyMediumDIY possible
Parts and labour€40–350
Time0.5–2.5 h

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

What to check first

  1. Check thermostat
  2. Check coolant level
  3. Watch temperature rise on a scan tool

Parts involved

thermostatengine coolant temperature sensorcooling system

Related codes

P0128P0126P0116P0117P0118

References: law.cornell.edu, fordservicecontent.com, mitsubishitechinfo.com, hella.com.