Fault code P0125 is called “Insufficient Coolant Temperature for Closed Loop Fuel Control” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.
Technical description and explained code P0125
To get the most out of every drop of fuel, the modern engine monitors and adjusts a number of parameters. Including oxygen content, ignition timing, valve opening time, injector pulse width and more.
Among all this, the temperature of both the fuel itself and the intake, as well as the cylinders, is very important. Of course, heat is released when the fuel burns, but it must be kept within a certain range.
If the temperature is too high, it can cause the engine to hum, detonate, and even break down. On the other hand, if the temperature is too low, the fuel does not burn efficiently. This means that the engine control module (ECM) must inject more fuel than normal.
Until the controller determines that the engine has reached operating temperature, it starts the engine in “open loop” mode, that is, following pre-programmed parameters. In open loop mode, the controller does not use the feedback from the AFR sensors to fine-tune performance and emissions. Once the engine reaches operating temperature, the ECM switches to “closed loop” mode, using the AFR sensors to maintain performance and fuel economy.
If, within a certain time, the ECM controller detects that the engine has not reached the proper operating temperature and cannot go into closed loop mode. It interprets this as a fault and sets error code P0125.
The ECM will store the Diagnostic Trouble Code (DTC) in memory and may command the Malfunction Indicator Light (MIL) to illuminate. Diagnostic Trouble Code P0125 is defined as “insufficient coolant temperature for closed loop fuel control”.
Symptoms of vehicle malfunctions
The main signal that an error P0125 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.
It can also be warning signs such as:
- Check engine control lamp on the control panel will light up (the code will be recorded in the ECM memory as a malfunction).
- Increased fuel consumption.
- Reduced engine performance.
- Vehicle engine overheating.
- Other related fault codes in ECM memory may also be detected.
- There may be no symptoms other than the stored fault code.
This error P0125 is not serious, the car will be able to start and continue driving. But it is better to solve it as soon as possible, because improper heat exchange can lead to more serious consequences.
Factors that can cause this error code
The error code P0125 can mean that one or more of the following problems have occurred:
- Coolant temperature sensor circuit is broken.
- Coolant temperature sensor wiring harness or connector is damaged.
- Coolant temperature sensor is defective.
- Engine coolant level is low.
- Engine coolant thermostat does not open at proper temperature.
- Sometimes the cause is a defective PCM module.
How to fix or reset OBD-2 code P0125
Some suggested steps for troubleshooting and fix the error code P0125:
- Read all stored data and error codes with an OBD-II scan tool. To find out when and under what circumstances error P0125 appeared.
- Clear the error codes from the computer memory and test-drive the vehicle to find out if the error appears again.
- Then check the coolant level (the engine should be cold).
- Visually inspect the electrical wires and connections relating to the sensor for looseness and damage. Repair if necessary.
- Test the thermostat; if it has failed, replace it.
- Clear the error code from the computer memory again, test drive the vehicle to see if the problem is resolved.
Diagnose and repair of problems
The first step in troubleshooting error P0125, is to review the Technical Service Bulletins (TSB). For known problems with a particular vehicle.
Perform a thorough visual inspection to check the wiring for obvious defects such as scratches, scuffs, exposed wires or burn spots. Next, check connectors and connections for safety, corrosion, and contact damage.
Be sure to carefully check the integrity of the wire harnesses and secure any loose wires. If you find a burned wire, solder it and make sure it is properly insulated.
Check coolant and thermostat
Make sure the coolant level is correct, both in the radiator (when cold) and in the coolant overflow tank. Make sure that there are no leaks and that the sealed cap is working properly.
If there is not enough coolant in the system, the engine may not warm up properly. Because if the temperature sensor is not in contact with the coolant, it will not read the temperature.
Using a non-contact thermometer, or a real-time streaming scan tool, check to see if the engine is warming up properly. Normally, the upper radiator hose should stay relatively cold until the thermostat opens. After that, it will warm up quickly.
If the thermostat is open, the coolant will leak constantly, preventing the engine from reaching operating temperature. This can also be the cause of fault code P0125.
Use a thermometer or diagnostic tool to check the engine temperature after 10-15 minutes of operation. If it does not reach operating temperature, check the ECT sensor, wiring, coolant level, and thermostat operation.
On which vehicles does this problem occur most frequently
Fault code P0125 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:
- BMW
- Cadillac (Escalade)
- Chevrolet (Captiva, Lanos, Tracker)
- Ford (Explorer)
- Hyundai
- Lexus (GS300, RX300)
- Mazda
- Mitsubishi (Carisma, Colt, Eclipse, Galant, Grandis, Lancer, Montero, Outlander, Pajero, Space Star)
- Nissan
- Opel (Antara)
- Renault
- Ssangyong (Kyron)
- Suzuki (Grand Vitara)
- Toyota (Avensis, Camry, Corolla, Matrix)
- TagAZ (Tager)
- ZAZ (Chance)
Fault code P0125 can sometimes be found with other errors. The most common are the following: P0115, P0116, P0117, P0118, P0119, P0128, P0130, P0170, P0173, P0300, P0401, P0420, P0441, P0450, P1135.
