P0125
Fix within 1-2 weeksInsufficient Coolant Temperature for Closed Loop Fuel Control
Code P0125 means your engine isn't reaching operating temperature fast enough for efficient fuel control. Common causes: Stuck open thermostat (60%), faulty coolant temperature sensor (25%), low coolant (10%). Drivability: Yes, safe to drive, but fix within 1-2 weeks. Repair cost: $15-$60 DIY, $100-$350 professional.
Can I Drive With P0125?
Yes, safe to drive
No restrictions, but fix within 1-2 weeks to avoid poor fuel economy and potential long-term damage.
Stop driving immediately if: Overheating, steam from under the hood, or a flashing Check Engine Light (indicating a severe misfire, though not directly caused by P0125).
Symptoms of P0125
- 1Check Engine Light is on
- 2Engine takes a long time to warm up
- 3Poor fuel economy
- 4Heater blows cold air (especially at idle or low speeds)
- 5Engine may run rough or hesitate when cold
Common Causes of P0125
Parts most likely causing this code, ranked by probability
A thermostat stuck open prevents the engine from reaching its proper operating temperature, causing the computer to keep the fuel system in open-loop mode.
60% of P0125 cases are fixed by replacing the thermostat
A faulty coolant temperature sensor sends incorrect low temperature readings to the engine computer, even if the engine is warm, preventing closed-loop operation.
25% of P0125 cases are fixed by replacing the coolant temperature sensor
Insufficient coolant or air pockets in the cooling system can prevent the coolant temperature sensor from accurately reading the engine's temperature.
10% of P0125 cases are fixed by topping off coolant or bleeding the system
Damaged or corroded wiring or connectors to the coolant temperature sensor can cause intermittent or incorrect temperature signals to the engine computer.
5% of P0125 cases are fixed by repairing wiring or connectors
Check These First (Before Buying Parts)
- Check your coolant level in both the reservoir and the radiator. Top off if low.
- Visually inspect the wiring and connector to the coolant temperature sensor for any signs of damage or corrosion.
- Use an OBD-II scan tool to monitor the live coolant temperature data. See if the temperature rises steadily and reaches the normal operating range (typically 190-210°F).
How to Diagnose P0125
- 1Check coolant level in the reservoir and radiator. Top off if low.
- 2Inspect the coolant temperature sensor (CTS) wiring and connector for damage or corrosion.
- 3Monitor engine temperature using an OBD-II scanner to see if it reaches operating temperature (typically 190-210°F) within a reasonable time.
- 4Feel the upper and lower radiator hoses as the engine warms up. If both get hot at the same time from a cold start, the thermostat is likely stuck open.
- 5Test the resistance of the coolant temperature sensor with a multimeter (compare to specifications for your vehicle's temperature range).
P0125 on Popular Vehicles
Toyota Camry
2007-2024P0125 on a Camry often points to a failing thermostat. The coolant temperature sensor is also a common failure point. Ensure the cooling system is properly bled after any component replacement.
80% fixed by thermostat or CTS replacement
Honda Accord
2003-2024For Honda Accords, a stuck open thermostat is the leading cause of P0125. Coolant temperature sensors can also fail, sending incorrect readings. Always check for proper coolant levels first.
85% fixed by thermostat or CTS replacement
Ford F-150
2004-2024Ford F-150s with P0125 frequently have a thermostat that is stuck open. The coolant temperature sensor is another common component to check. Verify coolant levels and look for any leaks in the system.
80% fixed by thermostat or CTS replacement
Frequently Asked Questions
What does P0125 mean?
P0125 indicates that your engine's coolant temperature has not reached the necessary level for the engine computer to enter 'closed-loop' fuel control within a specified time after starting. This means the engine is running richer than needed.
Can I drive with P0125?
Yes, you can drive safely with P0125, but you should fix it within 1-2 weeks. Your vehicle will consume more fuel and produce higher emissions, but it is not an immediate breakdown risk.
Will P0125 clear itself?
No, P0125 will not clear itself. The underlying issue, such as a stuck thermostat or faulty sensor, needs to be repaired. The code will only clear once the problem is resolved and the system completes its diagnostic cycle without detecting the fault again.
How do I fix P0125 myself?
Start by checking your coolant level and topping it off if low. If that doesn't work, the most common fix is replacing the thermostat. If the thermostat is good, test or replace the coolant temperature sensor. Always bleed the cooling system after any coolant-related repair.
How much does it cost to fix P0125?
DIY repair costs range from $15-$60 for parts like a thermostat or coolant temperature sensor, plus coolant. Professional repair costs typically range from $100-$350, covering parts and labor.
P0125 keeps coming back - why?
If P0125 keeps returning, it means the root cause was not fully addressed. Double-check for air in the cooling system, ensure the new thermostat is functioning correctly, or consider if the coolant temperature sensor or its wiring is truly the problem. A faulty engine computer is a rare but possible cause.
Will P0125 fail emissions/smog test?
Yes, P0125 will cause your vehicle to fail an emissions or smog test. The engine running in open-loop mode means higher emissions, and the Check Engine Light itself is an automatic failure in most testing jurisdictions.
What's the difference between P0125 and P0128?
P0125 means the engine coolant did not reach the temperature required for closed-loop fuel control. P0128 specifically means the engine coolant temperature is below the thermostat regulating temperature. Both codes often point to a thermostat stuck open, but P0125 is a broader indicator of insufficient warm-up for emissions control.
P0125 on Honda Civic?
On Honda Civics, P0125 is most commonly caused by a thermostat stuck open. The coolant temperature sensor is also a frequent culprit. Check your coolant level first, then focus on the thermostat and CTS. These are straightforward repairs for most Civic owners.
Questions to Ask Your Mechanic
Did you check the actual coolant temperature readings with a scan tool to confirm the engine isn't warming up, or if the sensor is reading incorrectly?
Good answer: Yes, the scan tool showed the engine only reached X degrees Fahrenheit after 15 minutes, which is too low, or the sensor was reading X while the engine was clearly warmer.
What is the resistance reading of the coolant temperature sensor at ambient temperature and after the engine has run for a few minutes?
Good answer: At ambient, it was X ohms, and after running, it was Y ohms. This is outside the manufacturer's specified range for those temperatures.
Repair Cost Estimate
DIY Repair
Parts only
$15-$60
Shop Repair
Parts + labor
$100-$350
Save $85-$290 by doing it yourself
Difficulty
intermediate
Time
1-3 hours
Intermediate - requires basic mechanical skills, an OBD-II scan tool for diagnosis, and careful handling of coolant. Bleeding the cooling system correctly is important.
Cost of Waiting
Ignoring P0125 leads to significantly worse fuel economy and increased emissions due to the engine constantly running a rich fuel mixture. Over time, this can lead to carbon buildup on engine components and potentially damage your catalytic converter from unburned fuel, turning a $50 thermostat job into a $1,200-$2,500 converter replacement.
While You're In There...
You will drain some coolant when replacing the thermostat or CTS, so it's a good time to refresh or top off with new, correct specification coolant.
If you're replacing the thermostat, you'll be disconnecting hoses. Inspect them for cracks, bulges, or softness. Replacing old hoses prevents future leaks and repeat labor.
This is a critical seal that should always be replaced when installing a new thermostat to prevent leaks.
Tools You'll Need
- OBD-II scan tool
- Socket set
- Pliers
- Screwdrivers
- Drain pan
- Funnel
- Coolant
- Multimeter (for testing CTS)
P0125 is a common code related to your engine's cooling system. Most repairs are straightforward, involving a thermostat or sensor, and will restore your vehicle's fuel efficiency and proper operation.
- Family-owned since 1957
- 990,000+ happy customers
- Fast nationwide shipping
- Easy returns
Your Next Steps
Step 1: Check your coolant level and inspect the coolant temperature sensor (CTS) wiring. Top off coolant if needed and clear the code to see if it returns.
Step 2: If the code returns, use an OBD-II scanner to monitor live coolant temperature data. If the temperature rises very slowly or never reaches normal operating range, replace the thermostat.
Step 3: If the thermostat is good and the engine warms up, but the scanner still shows low temperatures, test the CTS with a multimeter or replace it. You'll likely need a new thermostat, a new coolant temperature sensor, and fresh coolant.