Openbay makes auto repair and service simple.

Compare estimates. Choose a shop. Schedule an appointment. Pay securely online.

How Openbay works

P0128 Diagnostic Trouble Code

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.

Get estimates for a P0128 diagnosis from nearby shops

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 overtax the catalytic converter. You might wind up spending more money if you defer a fix.

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

Get estimates from nearby shops

How Openbay Works

  • Tell us about your auto service needs

    Openbay offers hundreds of maintenance, diagnostic, and repair services: from oil changes and brake jobs, to major suspension, electrical, and engine work. If you're not sure, describe the problem and we'll make recommendations.

  • Get estimates from nearby shops

    We get you detailed service estimates from our network of thousands of auto shops — usually within a few seconds. Compare on price, location, ratings, amenities, and more.

  • Book and pay securely online

    Once you choose a shop, book an appointment that fits your schedule. When service is complete, you authorize Openbay to make a contactless payment with your saved card.

  • Earn Openbay Rewards

    When you complete a service, you earn 1% of the invoice total as Openbay Rewards. They're instantly added to your account for use on your next service.

  • Manage your maintenance history

    When you create an account, your service history and upcoming appointments are always available online. Time to clean out the glove box!