Engine Hot AC Off: What Does It Mean And How To Fix It?

(Last Updated On: March 14, 2024)

What action should you take when the warning light for Engine Hot AC Off is activated?

This warning light implies that the engine’s computer has identified a circulation problem causing the engine to run too hot. 

We’ll get into the Engine Hot AC Off warning details and explain how to fix it in this post. Let’s take it to the end with great tips that will help you understand this warning light and how to prevent the problem altogether. 

Here we go. 

What is the meaning of engine hot AC off?

Your car can give the warning in terms of two different messages: “Engine Hot AC Off” or “Engine Hot AC Turned Off”. In both cases, the electric cooling fan is not working correctly, or something is wrong with the cooling system. 

When this happens, you may feel the need to turn on the car’s air conditioner, but nothing will operate. The car shuts off the AC to reduce the heat and load, hence the “Engine Hot AC Off” warning. 

Another meaning could be that the wiring to your electrical components is faulty or you’re low on refrigerant. Either way, you’ll need to get to the bottom of why your engine is running too hot. 

Can I keep driving when my car warns “engine hot AC off”?

An overheating engine is a serious problem. The situation is all too familiar. You’ve parked your car in the sun for too long or have not taken the time to perform maintenance only until the “engine hot” warning comes on.

The first thing you’ll want to do is pull over and evaluate the situation, then turn off the engine. It’s important to know that driving with an overheating engine may cause permanent damage to the engine. 

So, check the engine if it is overheating, do not continue your journey, and call a professional mechanic for advice on the next steps.

If you’re in a situation where you can’t come to a complete stop, you can turn on the heat to the highest level. This process will help pull as much heat as possible from the engine bay. And while you do this, roll down the windows so that the heat flows out of the vehicle. 

Can I fix this problem myself?

It depends on what’s causing the warning light. In some cases, a simple DIY repair can be the fix you require. So, if you’ve managed to stop and have got DIY experience, the first thing you’ll need to do is inspect the cooling system. 

Here, look for any leaks from the radiator or hoses. A leak on the radiator hose requires waiting for a minimum of 30 minutes for the engine to cool down before attempting repairs.

Next, tighten the radiator clamps using a screwdriver. You may notice that the clamp has been loose for some time. If so, adjust the hose to make a secure fit. Then, go ahead and tighten it with the screwdriver.

For a hole in the radiator hose, the temporary fix is to patch it using insulating tape.

Causes and how to fix it

Using an OBD2 scanner to read the fault codes from the engine is another way to fix the “Engine Hot AC Off” warning light. This method can make DIYs or mechanics easily find out the reasons for this warning. 

1. Malfunctioning thermostat or temperature sensor

You will need to diagnose the engine to determine if you have a malfunctioning thermostat or temperature sensor. 

How to diagnose the “engine hot AC off” using a scan tool?

Connect a diagnostics scan tool to the OBD2 connector under the dash of your car. You can use a standalone, Bluetooth, or USB scan tool. 

Depending on the scanner, you may be asked for the vehicle information. If the scanner reads the VIN automatically, it will save you a few minutes.

The “Engine Hot AC Off” warning light triggers two trouble codes. The first is the P0118 code, and the second is the P0128 code. 

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How to fix the P0118 code?

The P0118 code stands for “Engine Coolant Temperature (ECT) Sensor Circuit High Voltage”. It means the engine coolant temperature circuit is getting high input. Notably, it indicates that the Electric Control Module (ECM) has read an ECT sensor output above 4.91V or lower than -40F. 

Some of the causes for this trouble code are a low level of engine coolant, faulty Engine Coolant Temperature sensor, or issues with the engine coolant thermostat. If you’re an experienced DIYer or mechanic, you should be able to inspect for disconnected or damaged sensor connectors. 

Then, carry out the necessary repairs. These include;

• Replace or repair the ECT connector 
• Replace or repair the wiring open circuit as you see fit
• Use a new sensor to replace the ECT 

How to fix the P0128 code?

The P0128 code stands for “Coolant Thermostat Temperature Below Regulating Temperature”. It means the engine coolant is not getting up to temperature fast enough. This shows that the engine is not reaching optimum temperature within the required time. The typical response helping to turn off the warning light is to replace the thermostat.

But First, Inspect for a Stuck Open Engine Coolant Thermostat

To do this, feel the radiator hose and keep track of how high the temperature of the coolant goes as it starts flowing into the radiator hose. You must be careful because you could get burned quickly.

The hose should remain barely warm to the touch until the thermostat opens and then quickly become warm as the hot coolant flows through the radiator hose. If the temperature increases slowly, you’re dealing with a thermostat stuck open or opening prematurely. It will need replacing. 

How to replace the thermostat?

• Locate the thermostat where the top radiator hose joins the engine. 
• Place a 2-gallon container under your working station to trap any escaping liquid. After you finish the job, you’ll replace the fluid.
• Remove the clamp which locks in the radiator hose.
• Pull the hose, and then the liquid will escape. 
• Remove the old thermostat by loosening the bolts holding it in place.
• Take out the gasket and scrape off any pieces of gasket that may be left behind. Please ensure they don’t fall back into the hole.
• Insert the new gasket in its place.
• Drop in the new thermostat and replace the bolts. 
• Replace the hose by screwing it back or clamping it. Then replace the fluid down the radiator fill hole.

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Why is the warning still there after replacing the thermostat?

It’s time to inspect the coolant sensor.

The coolant sensor is close to the exhaust manifold, next to the number one spark plug. Typically, it gets very hot sitting close to the exhaust manifold. All that heat causes damage over time. 

How to inspect coolant sensor

• Check out coolant level and condition. 
• Look for poor coolant conditions like excessive rust. If this is the case, your cooling system is clogged up, and it’s causing the thermostat to stick. 
• For bad coolant, flush the coolant system and then replace the coolant. 
• Check the coolant temperature with a multimeter. The ohm reading should change with the temperature. If this is not happening, you’ll need to look for damage in the sensor wiring and repair it. 
• Unplug the coolant sensor. Strip out the protection, including the grey clip. If damage has occurred, you will find cracked wires with the copper exposed. A damaged coolant sensor increases the resistance in the circuit, reducing the voltage going into the ECM. It causes a false low temperature reading on the engine. 
• You’ll need to replace the coolant sensor if this is the case.

How to fix the coolant sensor

You will need

• A new coolant sensor
• Pair of pliers 
• Solder wire
• Soldering iron 
• Heat shrink tubing 
• Lighter
• Black tape 
• Flexible conduit 

Steps 

• A new coolant sensor will not have the ends pre-stripped. 
• Use a pair of pliers to strip the ends. 
• Cut the insulation off the ends high enough that you leave healthy insulation on the wire. 
• Insert the shrink tubing and crimp connectors on each of the wires.
• Mesh the strands of the sensor wires with those of the connecting cables. At this point, the connection is strong enough for soldering.  
• Use a soldering wire and soldering iron to create a solder-filled connection.
• Center the shrink tubing over the connection and get one end to shrink by passing a lighter over it. Then, quickly go over the rest of the tubing on both wires. 
• Crimp connection as a second layer of protection.
• Push the crimp connector over the shrink tubing and repeat the shrinking process. 
• Tidy up the excess wire using the black tape.
• Put the flexible conduit back over the wired connection. 
• Finally, plug in the coolant sensor, and you’re done. 

The warning light should not come back. 

2. Fail radiator cooling fan

Your engine may overheat because the radiator cooling fan does not come on. If the cooling engine fails or burns out, the radiator fan will be disabled. You will need to physically inspect the fan because it will not trigger a fault code. 

If your car was running when you discovered the problem, leave it about 30 minutes for the engine and radiator to cool down before attempting any repairs. 

How to fix the problem?

If you don’t have access to 12V, check the fuses. Then, if there are any signs of damage, replace the fuses and proceed to reattach the fan. And remember to connect the wired connection.

These steps should fix the error if the radiator fan is causing the warning light. If not, the next cause should suffice. 

3. Low level of coolant 

If the engine is overheating, you may be low on coolant. In this case, you need to inspect for leaks in the radiator, hoses, or radiator cap. Fix the leak as necessary, and then open the coolant reservoir to refill it with coolant up to the full line. 

Read more: Low coolant light: Is it dangerous? And what should I do?

4. Blown head gasket 

The head gasket seals and protects the cylinders from engine oil or coolant infiltration to ensure maximum compression. However, mechanical forces, heat, vibration, and overheating can cause a blown head gasket. 

Some of the signs of a blown head gasket include a strong, sweet smell from heated coolant, low level of coolant, white exhaust smoke, engine overheating, and misfiring. 

But the only way to be sure is by having a mechanic take your engine apart and perform a visual inspection.

Before replacing a blown head gasket, your mechanic will apply a head gasket sealant to the cracks. Please make sure you pick one from a good brand like Bar’s Leak. 

If the head gasket is fully damaged, it will need replacing. But this is an expensive repair, so make sure that it is worth replacing instead of repairing. 

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Read more: Coolant Boiling in Reservoir: The Causes and How to Fix It

5. Bad AC compressor

A problem with the AC compressor will impact the entire air conditioning system. Some of the ways to diagnose a bad AC compressor include:

• Check for physical damage and oil leaks 
• Check temperature fluctuations 
• Inspect the clutch and see that it rotates freely
• Check engine refrigerant leaks 
• Listen for squealing and skipping noise

After verifying that you have a bad AC compressor, it should be changed. A professional mechanic is best-equipped to perform this repair.  

Read more: Car Shakes When AC Is On: Why and How to Fix It

How much will it cost to fix the “engine hot AC off” warning light in a repair shop?

The cost of resetting this warning depends on each cause and solution. If your head gasket is severely damaged, it will be replaced for around $2000. But if you only have to change a faulty coolant sensor, it is only about $200 at the repair shop. 

Tips to prevent your car engine from overheating

1. Inspect your car periodically

A technical car inspection prioritizes the engine. Among other things, it detects oil spills and traces of different liquids. It also requires a change of engine oil, air, and pollen filters. In addition, a technician will inspect and change the antifreeze liquid if necessary. 

2.  Perform regular coolant flushes and changes

Coolant flushing involves examining the radiator, draining it, and adding new coolant. You should aim for coolant flushes every 50,000-100,000 miles for regular driving or 30,000-50,000 miles for severe driving. 

3. Recirculate of fresh air setting for the A/C system

Regular use of the air-recirculation button ensures that your AC works at an optimum level. It allows your vehicle to be as cool as possible quickly. Hence, the engine bay will be cold at the start of your journey. 

4. Pay attention to your car’s temperature gauge

It’s essential to read and understand your car’s temperature gauge. It is as straightforward as checking for an indication that the engine is hot, cold, or in a safe zone, which will help you know how to react when a certain setting comes up. 

5. Check the engine coolant level regularly 

The coolant level should always be the same unless there’s a leak. So, it’s best to discover the leak in your free time instead of on the road. You’ll need to perform the check when the engine bay is cold since the cooling system is pressurized. 

Conclusion 

An overheating engine can spell lots of trouble. It can cause permanent damage to the engine, which will be thousands of dollars to fix. That’s why when the “Engine Hot AC Off” warning light comes up, you should not take it lightly. 

And as they say, “take care of your car, and it will take care of you”, prevention is the best way not to face an overheating engine. 

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