Causes, Symptoms, Severity and Cost

2017 subaru impreza sedan 20i sport fq oem 1 2048

2017 Subaru Impreza

Technical Description:

The engine’s coolant temperature has not reached the correct level within a specified time period.

What P0128 really means:

During the warm up period right after the car is started, fuel management strategy is to run the car rich until all temperature criteria are met, then allow the oxygen sensors to take over to fine tune. Emissions are much higher than ideal, so decreasing the time for warm up is essential for lowering pollution. Coolant temperature is monitored right before the thermostat by one of the coolant system sensors.

What are the causes of a P0128 code?

For proper and efficient warm up, the coolant needs to stay trapped inside the engine to absorb the heat until it reaches the right temperature. This is the thermostat’s job. A heat sensitive spring in the thermostat moves to open up the coolant passage when it’s hot enough, so the coolant begins to circulate to the radiator then back to the engine. In most cases, when the coolant is not reaching the right temperature fast enough, the fault lies with a thermostat either partially or completely open.

What is the severity of a P0128 code?

Minor. There is no immediate danger of breaking down on the side of the road. You should have time to plan for the repair, and set an appointment with a good mechanic. While not requiring immediate attention, this code should not be ignored indefinitely. When the coolant is not at the proper temperature, the car will run richer, which will cause carbonization (think of your gas grill!) inside the engine and also overtax the catalytic converter. You might wind up spending more money

What is the cost to resolve a P0128 code?

  • Estimated part(s) cost = $30-50
  • Estimated labor cost = $50
  • Estimated Total cost = $80-$100

Some cars, particularly European, have a thermostat assembly where the plastic housing and sensors come together. These can run into the $100 to $150 range. Installation can really vary depending on your make and model. Some thermostats are very easy to access and will run around $50 for the installation. Others are really buried, so the labor can jump up to the $200 to $300 range.

Keep in mind, pricing will vary by location and your vehicle make and model. Save time and money by using Openbay to compare pricing and book an appointment with a service center in your area.

Service article written by an ASE Master Technician

If you want this service performed, Openbay can help get qualified automotive service professionals to perform the work for you.

Common Service Intervals
Conventional oil change
Every 6,000 miles
Clutch fluid (Replace)
Every 30,000 miles
Cabin air filter (Replace)
Every 12,000 miles
Spark plugs (Replace)
Every 60,000 miles
Air filter (Replace)
Every 30,000 miles
Brake fluid (Replace)
Every 30,000 miles
Fuel filter (Replace)
Every 72,000 miles
Timing belt (Replace)
Every 96,000 miles

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