P0125: Engine takes too long to warm up for fuel mixture control

What P0125 means

When the engine is cold, the ECU uses a preset mixture and ignores the oxygen sensor. Once the coolant reaches a certain temperature it switches to precise mixture control. This code means that temperature is taking too long to arrive, or never arrives.

Most common causes

• Low coolant level
• Thermostat stuck open, so the engine cannot warm up
• Coolant temperature sensor faulty or reading low
• Loose or corroded coolant sensor connector
• Radiator fan running all the time because of a stuck relay

Symptoms

• Engine warning light on
• Temperature gauge rises very slowly or stays low
• The heater takes a long time to blow warm air
• Slightly higher fuel consumption, especially on short trips

Can you drive with P0125?

Yes, no rush You can drive normally. The car uses a bit more fuel and heats the cabin less well, so it is worth fixing without leaving it too long.

How to check it

Start the car from cold and watch the coolant temperature in live data: it should climb steadily in the first few minutes. If it levels off well below normal running temperature, suspect the thermostat; if it shows silly values or jumps around, suspect the sensor or its connector.

How to read and clear P0125 with Final OBD

Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P0125 with this same explanation and whether it’s confirmed, pending or permanent.

With Free you read this code with its short description for nothing, and clear it if the engine stores it over standard OBD. With Pro you get the full explanation, how the car was running when it was logged (revs, temperature, load) and clearing in every control unit.

Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before the ITV. It’s all in how to read and clear fault codes and in the ITV and OBD.

Similar codes

• P0121 Throttle or pedal position sensor A: out of expected range
• P0122 Throttle or pedal position sensor A: low signal
• P0123 Throttle or pedal position sensor A: high signal
• P0124 Throttle or pedal position sensor A: intermittent signal
• P0128 Thermostat: coolant not reaching normal operating temperature
• P0130 Oxygen sensor (bank 1, sensor 1): circuit fault
• P0131 Oxygen sensor (bank 1, sensor 1): voltage too low
• P0132 Oxygen sensor (bank 1, sensor 1): voltage too high
• P0100 Mass or volume air flow sensor circuit fault
• P0101 Air flow sensor range or performance problem
• P0102 Air flow sensor circuit low input
• P0103 Air flow sensor circuit high input

P0125 is a generic code, so it means the same on any make, for example on Citroën, Hyundai, Mini, Renault, Seat, Volvo. See what Final OBD does on your car in makes and models.