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Engine Hot AC Off – What Does It Mean and What Causes It?

Austin Parsons

Meet Austin

Austin holds a technical writing degree and has 5 years of experience working as a Technical Product Specialist at BMW. He is an avid car enthusiast who is constantly watching F1, consuming automotive content, racing on his simulator, and working on his Toyota’s and BMW’s. Austin’s technical writing skills, extensive automotive knowledge, and hands-on experience make him an excellent resource for our readers.

One of the most common warning lights associated with an overheating engine is the “Engine Hot AC Off” message, which can catch unsuspecting drivers off guard. This message is most common on GM cars with digital dash displays, but also affects a number of other makes and models as well. If you just received this message on your dash, it is important to pull over and shut off your vehicle immediately to prevent any further damage from occurring. 

In this article, we’ll explain the potential causes for an “Engine Hot AC Off” warning light and what the next steps are in solving the issue. 

Engine-hot-ac-off

What Does Engine Hot AC Off Mean?

To put it simply, an “Engine Hot AC Off” warning light indicates that there could be a significant issue with your vehicle’s cooling system. The “Engine Hot” light typically comes on in response to a vehicle’s engine surpassing normal operating temperature, causing the onboard computer to shut off any system that puts an unnecessary load on the engine, including the AC system.

A vehicle’s A/C system is closely linked to engine performance, as it uses rotational energy from the engine to transform refrigerant from a liquid to a gas and vice versa. While there are additional steps in a car’s AC system, the most important aspect in the case of an “Engine Hot AC Off” warning light is the fact that the AC’s compressor adds an additional load to the engine. This is also the reason that cars overheat when the AC is on, especially on particularly hot days. 

An “Engine Hot AC Off” warning light is typically accompanied by decreased performance from the vehicle, as the engine control unit (ECU) attempts to cool the engine by limiting its output. There are a number of potential underlying issues that can trigger an “Engine Hot AC Off” light. While we will cover most of these causes in more detail in the section to follow, a low coolant level, a malfunctioning electric cooling fan, or a failing thermostat are some of the most common reasons that an engine overheats. 

Is It Possible To Keep Driving With Engine Hot AC Off Message?

While it is technically possible to drive while an “Engine Hot AC Off” message is present, it is highly recommended to pull over as fast as possible to prevent engine damage. An overheating engine is one of the most detrimental things that can happen to a car, especially if it is for a prolonged period. If you drive for an extended period while your engine is overheating you can potentially do irreparable damage to your engine or seize it altogether. The best course of action is to pull off the motorway to a safe location as soon as possible.

Even if your destination is only a few minutes away, extensive engine damage can be done if you continue to drive with an overheating engine. To prevent spending more than you need to on repairs, it is a better idea to pull over to either assess the issue yourself or call for a tow to the nearest auto repair shop. 

What Causes An Engine Hot AC Off Light?

There are quite a few potential causes for an “Engine Hot AC Off” warning light. All of these potential causes relate to issues that could cause an engine to overheat. Some of the most common causes include the following:

  • Malfunctioning or weak electric cooling fan
  • A coolant leak
  • Low engine coolant level
  • Water pump failure

Overheating occurs when an engine isn’t cycling enough coolant through the block and cylinder heads, meaning that heat cannot be transferred away from the engine. Overheating can be the result of coolant loss, whether that be from a leak in one of the coolant hoses in the engine bay or from coolant being burned by the engine. It can also be caused by a faulty or broken component in the vehicle’s cooling system such as the electronic radiator fan or a failing water pump. Some of these issues are inexpensive and easy fixes while others can be more involved and costly.

Malfunctioning Electric Cooling Fan

An electric cooling fan, or radiator fan, plays a crucial role in maintaining an engine’s temperature. In essence, an electric cooling fan has the job of pulling air through a vehicle’s radiator. The fan cools the hot coolant in the radiator before being rerouted through the engine. This is especially important when a vehicle is at a stop with the engine running, as there is no incoming air from the vehicle’s movement. Electric radiator fans are used more commonly than engine-driven fans, as they don’t add any load to the engine.

 If the fan stops working or isn’t pulling in enough cool air, the coolant within the radiator does not cool off and the hot coolant is sent back through the engine. This can cause the engine to overheat very quickly. It is generally pretty easy to identify is a radiator fan isn’t working. 

One way to test is by letting your car sit until the engine is cool. You can then turn the vehicle on and, keeping an eye one the temperature gauge, monitor the coolant temperature until it reaches operating temperature (usually when the needle is right in the middle of the temperature gauge). If you don’t hear the radiator fan activate at this point and the temp continues to rise, the cooling fan is a likely culprit.

Electric Cooling Fan Electrical Malfunction

Price to repair: $20-$300

DIY difficulty: Easy/Moderate 

Ultimately, there are a number of reasons that a vehicle’s radiator fan would stop working. One of the first areas that you should inspect is the fuse box. Electric radiator fan fuses can blow, causing the fan to stop working. The fuse box should be checked first, as it is the least expensive and easiest-to-fix issue that can cause a radiator fan to stop working. 

As an electrical part, the fan needs to receive an electrical signal from the car’s ECU to tell it to turn on. If there is an issue with the connection between the fan and the ECU, the fan will not operate correctly. There could also be a problem with one of the sensors used to gather the status of the vehicle’s cooling system. 

The car’s engine coolant temperature sensor (ECT sensor) might not be reading the vehicle’s coolant temperature correctly, preventing the fan from switching on. Corroded electronics or damaged wires can also cause a radiator fan to stop working, so look out for that as well.

Electric Radiator Fan Mechanical Issue

Price to Repair: $100-$600

DIY Difficulty: Moderate

Beyond just the electronics associated with an electric radiator fan, there are some mechanical gremlins that can also cause the fan to stop working. With that being said, electrical issues are far more common than mechanical ones. After many miles of driving, most components on a vehicle need to be replaced or serviced. A radiator fan also falls under this umbrella. Electrical radiator fans tend to be far more reliable than engine-driven ones. However, fan motors can degrade and either break completely or be very ineffective. At that point, the fan motors will need to be replaced.

Additionally, there can be an issue with the fan’s condition itself. Over time, debris and other foreign objects can worm their way into the engine bay. If a radiator fan blade hits a piece of debris, it can do sizable damage to a fan’s function overall. For that reason, it is important to check the state of your radiator fan.

Coolant Leak

It would be fair to say that coolant is a car’s equivalent to blood. While they might serve different purposes, they’re both necessary for everything to operate properly. As we have already covered, coolant’s primary job is to ensure that an engine remains in a particular temperature range without it ever exceeding its normal operating temperature. If there is a leak somewhere, there is a decreased amount of coolant in the system. Eventually, the majority of coolant will escape, leaving little left in the system and causing the car to overheat.

Old or Cracked Coolant Hoses

Price to Fix: $10-$200

DIY Difficulty: Easy

Coolant leaks are extremely common due to the fact that there are a ton of coolant hoses that route coolant to multiple different places in the engine bay. As a result, there are tons of connection points that can be gradually leaking some coolant. Most coolant hoses are also made from rubber or another flexible-but-brittle material that cracks with age. Generally, the older a car is, the more likely it is to have coolant leaks for this very reason.

There are a few easy ways to tell if your vehicle is leaking coolant. One way is simply to look under the hood for any light-colored residue on parts near coolant hoses. Pay special attention to the junctions where coolant hoses meet other parts, as connection points are common areas for leaks. Inspect the coolant hoses themselves, when the vehicle is off and cool, checking for cracks or signs of damage. Alternatively, you can drive the vehicle until it is up to operating temperature and park above a clean piece of pavement. If there is a puddle under the vehicle when you pull away, a leak is likely. 

You can also check for a coolant leak based on smell. Antifreeze has a very distinct smell that is immediately noticeable, especially when it comes in contact with a hot component. For those that don’t know, coolant has a sweet, almost maple-syrup-y, type of smell. Sometimes it is possible to sniff around the engine bay to see what area is producing the most pungent aroma.

Coolant Level Low

Price to Fix: $0-$50

DIY Difficulty: Easy

One of the very first things to check after an “Engine Hot AC Off” message appears on your dash is the vehicle’s coolant level. It is extremely important that you do not open either the radiator cap or expansion tank cap while the vehicle is hot. This can result in serious injury from coming in contact with boiling coolant. With that being said, once you have stopped at a safe location and have let the vehicle cool down, there are a couple of ways to check your vehicle’s coolant level. 

The first way is by checking the coolant level in your radiator. Of course, this varies from car to car, as not all vehicles have radiator caps located in the same place and some cars don’t have radiator caps at all. But, the process is simple. After the vehicle has cooled, open the radiator cap typically located near the very front of the engine bay. Look into the radiator filler neck and if you cannot see coolant then your coolant level is low. If you can see coolant, the level is fine.

Another way to check your vehicle’s coolant level is to look at the markings located on the coolant overflow/expansion tank. Make sure that you are parked on a flat surface or the coolant reservoir won’t be accurate. There are typically two lines on the outside of the semi-transparent tank. The two lines are generally labeled “Low” or “Full” or something to that effect. If the coolant level is below the “Full” line, you’ll need to add coolant.

Water Pump Failure

Price to Fix: $400-$800

DIY Difficulty: Difficult

In terms of cooling system components, a vehicle’s water pump is one of the most vital. A vehicle’s water pump plays a massive role in ensuring that a vehicle’s engine remains at a steady and normal temperature. The primary job of a water pump is to pump coolant out of the radiator and circulate it around the engine. This draws heat away from areas of the engine that are getting too hot. Without a water pump, a vehicle’s coolant would sit stagnant in the radiator. With the engine running, a failed water pump can cause an engine to overheat very quickly. 

As a rule of thumb, water pumps tend to have a lifespan of around 60,000 to 90,000 miles. At that point, it is a good idea to have the pump replaced. Over time, the internal gaskets and seals that are responsible for containing coolant inside the water pump degrade causing coolant to escape. If your vehicle is overheating and displaying an “Engine Hot AC Off” light and you have already checked your cooling system for leaks, it might be due to a failing water pump. 

There are typically a few telltale signs that your vehicle’s water pump is failing. If you notice that your vehicle is leaking coolant under the front middle of your car there is a chance that the leak is coming from the water pump. Due to the fact that a vehicle’s water pump is belt driven, a high-pitched whining sound from the engine bay can also indicate that the water pump has loose bearings or that the belt is too loose. 

How Much Does It Cost To Fix Engine Hot AC Off Light?

When it comes to how much it will cost to repair the issue that caused the warning light, the final figure will vary depending on a few factors. What is the underlying problem? Are you planning on doing any of the labor yourself? Are the parts expensive? These are all questions that can factor into the final price.

Generally speaking, cooling system issues can either be extremely cheap or quite hefty. If the light was triggered by a lack of coolant in the radiator, causing the car to overheat, the solution is as easy as simply adding more coolant. Replacing a radiator cooling fan relay or fuse is also very inexpensive. Rubber coolant hoses are a dime a dozen from the manufacturer. They can usually be installed by drivers with limited automotive knowledge as well. With that being said, it is important to have your vehicle towed to a reputable repair center if you don’t feel comfortable doing the work yourself.

While the most common underlying issues that can trigger an “Engine Hot AC Off” light are easy and inexpensive repairs, some of the more serious cooling system issues can get pricey. While you can generally find electronic cooling fans for cheap, it might take a mechanic a bit of time to install them, leading to inflated labor costs. The same is true for replacing a water pump, as that can be a very involved job on some vehicles.

As a ballpark figure, it can cost anywhere between $10 and $800 to fix the underlying issue that triggered the light. 

How Do You Prevent Your Car From Overheating?

At its core, the “Engine Hot AC Off” light is almost always caused by an overheating engine. Luckily, there are ways to preventatively ensure that your vehicle remains safe from overheating. 

One of the best ways to ensure the safety of your engine is to frequently check your vehicle’s coolant level. Low coolant is what kills the majority of overheating cars. As such, it is imperative to check both the radiator and expansion tank often. A good rule of thumb is to check your coolant level every other time that you fill up for gas. That will allow you to stay on top of your vehicle’s cooling system health.

While not necessarily preventative “maintenance,” it is also crucial to pay attention to your vehicle’s temperature gauge. Most car owners disregard the temp gauge as many people underestimate how important keeping an engine’s temperature low is. Ultimately, if you aren’t paying attention to your vehicle’s temp gauge and the vehicle overheats you could be looking for a new car. You don’t have to stare at the gauge, but glance over at it every once in a while. 

Lastly, it is hard to overstate the importance of staying on top of regular service intervals. Oftentimes, car owners will turn down recommended service items due to cost or time constraints. That is completely understandable. However, it is important to not forget about these items and get them done eventually. As it relates to the warning message, it is important to get a radiator flush and coolant exchange every 30,000 miles, replace your water pump every 60,000 to 90,000 miles, and replace brittle coolant hoses as necessary. 

Engine Hot AC Off Summary

It is never fun to see a new warning light pop up on your vehicle’s dashboard. That is especially true if you aren’t sure what the light even means. If the “Engine Hot AC Off” warning light appears, there is likely an issue with your vehicle’s cooling system. Essentially, the vehicle automatically turned off the AC in order to reduce the strain on your vehicle’s engine. It is important to pull over and turn the vehicle off quickly after seeing this light. If you keep driving while this issue is present, you could do permanent damage to your engine.

There are numerous potential underlying causes for the warning light. Most of these issues relate directly to the vehicle’s cooling system. Some potential causes include a low coolant level, a coolant leak, a malfunctioning cooling fan, and a bad water pump. All of these issues can cause your vehicle to overheat and trigger a warning light. Checking the easy-to-fix causes first, like the radiator fan relay, fuse, and coolant hose condition is a good idea to eliminate them first. If none of these are the cause, you can move on to more involved issues.

The “Engine Hot AC Off” warning light can be an alarming one to see. There is some cause for concern, as it can lead to expensive repairs down the line if you don’t take care of the issue immediately.

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