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The Best OBD Scanner for Diagnosing Overheating Engine

By Joe Ballard
Published on July 1st, 2024

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Maintaining a constant engine temperature is challenging, especially in extremely hot or cold climates. However, you can confidently diagnose and fix engine overheating issues with the right tools, such as an OBD scanner.

Overheating Engine

In this article, I will present the most common causes of overheating, the warning signs you should watch for, how you can effectively use an OBD scanner to identify and fix a problem, and the best ways to avoid a problem.

Common Causes of Overheating

The cooling system, a crucial component of most gas-powered vehicles, is complex. It includes a radiator with coolant that circulates within the engine, an electric fan to keep the radiator cool, a thermostat to control coolant flow, and a water pump to move the coolant through the system. Understanding these components is critical to maintaining your vehicle's temperature. A failure of any of these components can impact engine temperature, and here is how:

  • Coolant system leaks cause a loss of coolant, which increases engine temperature. The coolant can leak from several areas, such as the radiator cap, hoses, water pump, thermostat gasket, or engine manifolds.
  • A thermostat failure will prevent the coolant from flowing properly through the engine. If it is stuck open, the engine may not reach operating temperature. If stuck closed, it will restrict the coolant flow and increase engine temperature.
  • The water pump circulates coolant throughout the engine. If it is not working correctly, then coolant does not flow efficiently, increasing engine temperature.
  • The cooling fans help dissipate heat from the radiator. Malfunctioning fan motors, a defective fan relay, or broken fan blades will impact heat dissipation from the radiator and increase engine temperature. This is more noticeable at low speeds or while idling because there is no airflow through the radiator while the vehicle moves.
  • A clogged radiator is usually caused by a buildup of dirt, debris, or corrosion over time. The clog restricts the coolant flow and reduces the radiator's ability to dissipate heat, resulting in a higher engine temperature.
  • A faulty radiator cap will prevent the radiator from maintaining the proper pressure in the cooling system. A loose cap could cause coolant to boil at a lower temperature, resulting in high engine temperature.
  • Blocked coolant passages inside the engine are usually the result of dirt, debris, or corrosion over time. Like radiator blockage, heat buildup in the engine cannot dissipate, resulting in high engine temperature.
Overheating Engine

What are the warning signs?

Typically, the first noticeable sign that your vehicle is overheating is the engine temperature warning light coming on. This may or may not be accompanied by the check engine light (CEL), depending on whether the ECU registered a fault code. Some of the other warning signs that your vehicle is overheating include the following:

  • If your vehicle has an actual temperature gauge, it should generally be between hot and cold. If it is pointing towards the hot side, the vehicle is overheating.
  • If there is smoke coming from the engine compartment, then the engine is too hot.
  • If the coolant level appears low, look at the overflow tank and note the level based on the hot/cold lines.
  • A coolant leak overflow could occur if the radiator cap is not on tightly.
  • If the radiator fan is not running, the coolant will get too hot and not cool the engine properly.
  • If the coolant leaks from any hoses or the water pump, the engine will overheat.
  • If the serpentine belt or fan belts are not intact, the water pump and fan will not cool the engine properly.

If you experience any of these warning signs, it is essential to pull over as quickly as possible, turn the engine off and let it cool down. If you continue to drive the vehicle that is overheating, you may end up with issues such as:

  • Steam emanating from under the hood
  • A hot engine hood
  • Thumping sounds from under the hood
  • Reduced engine power
  • Coolant overflow onto the ground
  • The vehicle may suddenly stop dead in its tracks

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Using an OBD Scanner to Identify the Issue

As you have seen, many of the issues associated with overheating are mechanical. Components like the radiator, water pump, fans, and coolant system leaks are relatively easy to identify, but what about the sensors and relays behind the scenes that are just as important? These electrical components provide valuable feedback to the ECU to give an early warning of potential overheating. Using an OBD scanner from Innova paired with the RepairSolutions2 app will interpret error codes that will enable you to identify and fix overheating issues. Let's take a look at some of these error codes:

  • P0217 – indicates that the engine coolant temperature is too high and is close to overheating. This code will usually trigger the CEL. The other indications include a temperature warning light or the temperature gauge needle over in the hot range. Inspecting the cooling system's mechanical components will usually identify the problem.
  • P0128 – indicates that there is a problem with the thermostat and the engine is overheating. As usual, this is only an indicator of a potential issue to point you in the right direction generally.
  • P0480 – is a general trouble code that indicates a problem with the cooling fan control circuit. The other associated codes include P0481 and P0482. The leading causes of this code are that the fan is faulty, there is a poor electrical connection, there is fan relay failure, and there is a bad coolant temperature sensor. This is a very common problem that will always trigger the CEL.
Innova 5610 paired with RepairSolutions2

Several other codes indicate a cooling system problem. Using my 2003 Mazda Miata as an example, this vehicle runs hot most of the time, but this is normal. To ensure that all systems are working normally, I attached the Innova 5610 OBD scanner and ran the Live Data tests. The sensors were all measuring in range, so I am sure there are no issues (I also did not have any stored codes). If I had detected an issue, I would move to the next step, which is performing further analysis to pinpoint the actual problem.

Key Takeaways

Several potential mechanical components must work together to ensure your vehicle operates within a specific temperature range. A failure of any of these components will result in an overheating situation, so it is essential to heed the warning signs and take the appropriate action to resolve the issue.

Your OBD scanner is invaluable for identifying potential problems contributing to an overheating engine. Your vehicle was designed to include sensors that monitor the systems responsible for maintaining the engine temperature. When an issue is identified, a DTC is sent to the ECU for further analysis. This trouble code will assist you with identifying the problem and enabling you to fix it.

There are things that you can do to avoid engine overheating. Most of them are very simple and, if done regularly, will ensure that you identify a potential problem that could cause your vehicle to overheat. Let's take a look:

  • Cooling system maintenance: Check the vehicle's coolant level and age. Coolant that is several years old may need to be changed per the manufacturer's guidelines in the owner's manual.
  • Check for coolant leaks: Look around the hoses, radiator cap, water pump, and thermostat housing for any signs of a leak. Also, look on the ground for any puddles of coolant.
  • Check over the radiator and cooling fans: A good maintenance item is to clean the radiator fins from debris, dirt, and bugs to ensure proper airflow. Also, check the cooling fans to ensure they are operating correctly.
  • Engine belts and hoses: Inspect the belts and hoses for any signs of wear. A failing fan belt will usually emit a screeching sound when you accelerate due to slipping on the pulley. Hoses that have cracks or are very soft are nearing their end of life and should be replaced.
  • Periodically run an OBD scan of all systems: Advanced OBD scanners (like the model 5610 from Innova) have tests that will check the system/actuators and enable you to run other service checks proactively. Many of these tests are performed in a “Live Data” mode so that you can monitor systems under load.


No one wants to deal with an overheating situation, which is why it is so important to do all of the necessary preventative maintenance to avoid it in the first place. You can see that there are several relatively simple checks that you can perform to prevent an overheating situation.

Understanding what causes overheating and heeding the warning signs will arm you with the knowledge to deal with any issues that may come up. A skilled DIYer can perform some fixes, but others require an experienced service technician. Whatever path you decide to take, the key takeaway is that the higher the temperature in your engine, the more damage is inflicted and the more repairs will cost.

Replacing a hose, a radiator cap, a thermostat, or a belt may cost a few hundred dollars, but if the engine is damaged and needs to be replaced, you are looking at several thousand dollars. Just based on these costs alone will justify an investment in a good OBD scanner as it will offer detailed insights into cooling system operations to enable targeted troubleshooting and repairs.

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