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P0125 – Meaning, Causes, Symptoms, & Fixes


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What Does Code P0125 Mean?

  • P0125 definition: Insufficient coolant temperature for closed-loop fuel control.
  • Issue Severity: LOW – Continued driving for a short period of time is okay.
  • Repair Urgency: Get this fixed within the next month to prevent poor fuel economy and non-functional heat.
  • Diagnosis: This trouble code can appear with no driveability concerns, but it can also cause the vehicle’s heat not to work and poor fuel economy. It should be fixed to get the vehicle back to optimum running conditions.

When this code is triggered, the Engine Control Module (ECM) has used its internal logic to determine that the engine hasn’t reached an operating temperature at the proper time. It does this by checking the Coolant Temperature Sensor value as the vehicle is warming up and comparing it to what it should be at certain times. If it seems that the vehicle’s coolant isn’t getting as warm as it should as fast as it should, it triggers this code.

P0125 Causes

There are many potential causes of code P0125.

  • Low engine coolant
  • Stuck open thermostat
  • Missing thermostat
  • Faulty coolant temperature sensor

P0125 Symptoms

  • Check Engine Light
  • Poor fuel mileage
  • Temperature gauge reads cold all the time
  • Heat blows warm or cold when it should be hot
  • No noticeable adverse conditions in some cases

How Do I Fix Code P0125?

With a coolant temperature fault, the first step is to get it diagnosed to figure out what is causing the problem. 

If your vehicle has this fault and you’re not comfortable diagnosing this issue at home, we recommend finding a RepairPal certified shop nearby to pinpoint the problem and give an accurate estimate for repairs. 

These shops can not only help you figure out what’s going wrong before you waste time and money on the wrong parts, but they also offer a minimum 12-month, 12,000-mile warranty and stand behind all their estimates with guaranteed fair pricing.

> Find a RepairPal Certified Shop Near You

How Much Does It Cost to Fix Code P0125?

P0125 can be caused by anything from a low coolant level to a bad temperature sensor to a faulty thermostat. It’s impossible to give an accurate estimate without properly diagnosing the issue first. 

If you take your car to a shop for diagnosis, most shops will start with an hour of “diag time” (the time spent in labor diagnosing your specific issue). Depending on the shop’s labor rate, this typically costs somewhere between $75-$150. Many, if not most, shops will apply this diagnosis fee to any required repairs if you have them perform the repairs for you. From there, a shop will be able to give you an accurate estimate for repairs to fix your P0125 code.

Possible Repair Costs for P0125

For error code P0125, one or more of the below repairs may be needed to solve the underlying issue. For each possible repair, the estimated cost of repair includes the cost of the relevant parts and the cost of labor required to make the repair.

  • Thermostat $220-$260
  • Coolant Temperature Sensor $150-$200
  • Top off coolant $10

DIY Steps to Diagnose Code P0125

Engine code P0125 could be caused by a number of things, including a low coolant level, a bad temperature sensor, or a faulty thermostat. If you’d like to try to fix code P0125 at home without throwing money at parts, you’ll want to follow the steps below for proper diagnosis. Keep in mind this is an intermediate-level diagnosis and repair and not recommended for beginners. Diagnosis requires more specialized equipment beyond what the FIXD Sensor can provide and it can be a time and labor-intensive process for inexperienced DIYers.

DIY difficulty level: Intermediate

This repair requires mechanical knowledge and is not recommended for beginners.

Tools/parts needed (our top picks from Amazon):

  • FIXD
  • Basic Hand Tools
  • Vehicle-Specific Service Manual


Use FIXD to scan your vehicle to verify P0125 is the only code present.


Check for any Technical Service Bulletins (TSB) for your make and model vehicle. Some cars have an ECM update to address this particular code.


Make sure that both your radiator and your coolant reservoir are filled up with coolant to the proper levels. If either is low, top it off and bleed the air out of the system as described here.


Using a multimeter, check the coolant temperature sensor voltage. Refer to your vehicle’s specific service manual to find out what this voltage is supposed to be. If your reading is different, replace the coolant temperature sensor.


If the coolant temperature sensor is good, the thermostat is most likely stuck open or missing. Replace the thermostat and fill the cooling system with new coolant.

Common P0125 Diagnosis Mistakes

Not checking the coolant level before replacing parts.

Still Need Help Fixing Code P0125?

If you’ve followed the steps above and are still experiencing check engine code P0125, please contact the FIXD Mechanic Hotline if you’re a FIXD Premium subscriber or find a RepairPal certified shop near you to get the right repairs at a fair price.

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Fixed It But The Check Engine Light Is Still On?

Check engine light sometimes need to be reset manually, check out our article:

How to Reset Your Check Engine Light | 4 Ways To Clear It (With or Without a Scanner)

Justin Hughes

Recovering autocross and track day enthusiast. Once turned a VW Jetta into a pickup truck. Lives in a van down by the river. Dream car: 2001 Subaru WRC rally car.

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We’re here to help you simplify car care and save, so this post may contain affiliate links to help you do just that. If you click on a link and take action, we may earn a commission. However, the analysis and opinions expressed are our own.


About the Author

Justin Hughes

Justin Hughes

Recovering autocross and track day enthusiast. Once turned a VW Jetta into a pickup truck. Lives in a van down by the river. Dream car: 2001 Subaru WRC rally car.

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