Low coolant light comes on when AC, defrost or heater is on, but only if the car is in gear and stopped, what’s wrong with my car?

My low coolant light comes on when AC, defrost or heater (I will just say AC for short, the problem applies to all) is on, but only if the car is in gear and stopped. If I stop at a stoplight with the AC on the light comes on within 30 seconds, the light goes off as soon as the car begins moving again or if I turn the AC off. If I sit through the light with the AC on and the light lit up, at the next light the low coolant light will not come on. If the car is on and in park with the AC on the light doesn't come on. This happens in all weather and temperatures, at any time of day, whether t
Experienced mechanics share their insights in answering this question :
First, you want to make sure your cooling system is full. Check the radiator not the coolant jug. And check it when it is cold. If it needs coolant, add some. Of course, I don’t feel this problem is an actual low coolant condition. I would expect to find an electrical failure in the instrument cluster or from a component or wiring harness that is connected to the instrument cluster.

As a technician, I have access to reports from technicians across the country. I could not find any reports of this problem, so diagnosing this will require an experienced tech as this is not a common problem. In addition, this happens at intermittent times making it difficult to recreate. The most challenging part of this diagnosis will be recreating the symptom. I suspect it has something to do with the brake switch circuitry because it only seems to happen when you have your foot on the brake. I would begin my diagnosis there with a wiring diagram and test light in hand. The brake switch, instrument cluster, and environmental controls all interact with each other. Something is crossed either because of a failed module or damaged wiring in a harness.

Aside from making sure the coolant is full, this will not likely leave you on the side of the road. If you take it in to be diagnosed, be prepared for them to spend more time than usual to figure it out. Since it isn’t a key problem, you may need to live with it until it completely fails making it much easier to diagnose. Either way, I do recommend having a certified mechanic diagnose the warning light to make sure there isn’t anything serious going on.

Good luck.

How to Identify and Fix Common car Problems ?

Our sources include academic articles, blog posts, and personal essays from experienced mechanics :

If your AC coolant is low, there is a leak somewhere. To simply add more coolant without isolating and repairing the leak is to literally watch your money disappear into thin air. A trained professional will identify and repair the leak, making the system properly sealed and closed once again.
The most common reason for the coolant light to become illuminated is simply that the coolant level is too low. There may be a floating sensor in your coolant tank that triggers the warning light when the level drops. You may need to book a coolant change.
The indicator is telling you that the fluid level is below the sensor, however, once you start driving and the engine heats up, the light should go off. If your coolant light stays on even after driving for a few minutes, then it`s time to check your coolant levels and the coolant sensor.
Low coolant: Whether caused by a leak or water evaporation, low coolant is the most common source of poor heater output. Thermostat: A stuck-open thermostat prevents the engine (and coolant) from heating up. Heater core: A clogged heater core restricts coolant flow, giving up little or no heat.
AC system leaks and/or a faulty evaporator temperature sensor can cause poor AC cooling. The failed sensor can prevent the AC compressor from coming on.
If your coolant light is on, but the coolant is not low in the reservoir and it appears there are no leaks, then your vehicle may have a coolant sensor malfunction. A faulty coolant sensor can falsely trigger the dashboard warning light.
your coolant level is low

solution: this is potentially an easy fix. simply top up your coolant to the “max” or “full” level when the engine is cold. use a 50/50 coolant-and-water mix, as specified in your owner`s manual.

If your car has a low coolant you can drive for some time. It really relies on the level of coolant. If it is low but it is above the minimum, you can drive your car for a few days. But if it is below the minimum, please do not even try to run your engine.
Coolant Leaks

Oftentimes when the thermostat fails, it remains in its closed position. As the engine overheats, coolant will overflow out of the thermostat housing. This means that coolant leaking out of your engine could be a sign that your thermostat has gone bad.

Can you top your coolant up with water? Coolant should only be topped up with water in case of an emergency when the coolant liquid level is lower than it should be. While topping up with water will help you get safely to the nearest RAC Approved Garage and identify any issues, it shouldn`t be relied upon.
In fact, most units only need to be recharged once every two to five years – and sometimes even longer than that. The main exception to this rule is if there`s a leak in the system, which will cause the refrigerant level to drop over time.
The short answer is yes, coolant can affect air conditioning performance in a number of ways. Typically, coolant can affect your AC`s temperature, humidity, and airflow. Your AC`s temperature may be affected by the proximity of your car`s interior to your engine.
The AC sensor on your thermostat is located near the evaporator coils. Indoor air moving toward the return vents passes by the sensor and coils. In turn, the sensor reads the temperature and checks if it matches what you`ve set on the thermostat.
There are two temperature sensors in some vehicles, one to send information from the engine system to the control unit and another from the control unit to the dashboard. The device follows the principle of dependence of potential difference in temperature.
Start your car`s engine and allow it to idle. Look through the radiator filler neck to see if the coolant flows. At this time, it should not be flowing as your car has not reached the operating temperature to cause the thermostat to open. If you find the coolant is flowing, it means the thermostat valve is open.
In the winter, it keeps it from freezing, hence the dual name. Your A/C system uses a type of refrigerant (commonly called Freon) to cool the interior of your vehicle. Having a coolant flush performed will not help your A/C stay cool, or visa versa.
The short answer is yes, coolant can affect air conditioning performance in a number of ways. Typically, coolant can affect your AC`s temperature, humidity, and airflow. Your AC`s temperature may be affected by the proximity of your car`s interior to your engine.
In the winter, it keeps it from freezing, hence the dual name. Your A/C system uses a type of refrigerant (commonly called Freon) to cool the interior of your vehicle. Having a coolant flush performed will not help your A/C stay cool, or visa versa.
In theory, your air conditioner should never need more freon refrigerant. You will only need more refrigerant if there is a leak in your cooling system. It could be leaking out slowly over time, which is a problem because not only will this affect your AC, it is very expensive to replace.
In the winter, it keeps it from freezing, hence the dual name. Your A/C system uses a type of refrigerant (commonly called Freon) to cool the interior of your vehicle. Having a coolant flush performed will not help your A/C stay cool, or visa versa.
Your engine`s cooling system uses coolant, also known as antifreeze, to keep your engine cool even on the hottest days. A separate cooling system for the inside of your vehicle is the air conditioning system. It uses refrigerant (commonly called Freon) to keep you and your family cool and comfortable.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

Low coolant light comes on when AC, defrost or heater is on, but only if the car is in gear and stopped, what’s wrong with my car?
ANSWER : First, you want to make sure your cooling system is full. Check the radiator not the coolant jug. And check it when it is cold. If it needs coolant, add some. Of course, I don’t feel this problem is an actual low coolant condition. I would expect to find an electrical failure in the instrument cluster or from a component or wiring harness that is connected to the instrument cluster.

As a technician, I have access to reports from technicians across the country. I could not find any reports of this problem, so diagnosing this will require an experienced tech as this is not a common problem. In addition, this happens at intermittent times making it difficult to recreate. The most challenging part of this diagnosis will be recreating the symptom. I suspect it has something to do with the brake switch circuitry because it only seems to happen when you have your foot on the brake. I would begin my diagnosis there with a wiring diagram and test light in hand. The brake switch, instrument cluster, and environmental controls all interact with each other. Something is crossed either because of a failed module or damaged wiring in a harness.

Aside from making sure the coolant is full, this will not likely leave you on the side of the road. If you take it in to be diagnosed, be prepared for them to spend more time than usual to figure it out. Since it isn’t a key problem, you may need to live with it until it completely fails making it much easier to diagnose. Either way, I do recommend having a certified mechanic diagnose the warning light to make sure there isn’t anything serious going on.

Good luck.

Read Full Q/A … : Low coolant light comes on when AC, defrost or heater is on, but only if the car is in gear and stopped, what’s wrong with my car?

No coolant in the reservoir. Seen low coolant message. I added 2 quarts of 50/50 coolant. Still getting the message. How much coolant doe it need?
ANSWER : Hi there. For the coolant light to go out, you would need to have the coolant between the low line and the full line for the light to go out. If the coolant is low and keeps on being low, then look for any signs of coolant leaks. You may have to use a coolant pressure tester to pressurize the reservoir to allow the leak to be found.

If you need further assistance with the coolant being low and the warning light being on, then seek out a professional, such as one from Your Mechanic, to help you.

Read Full Q/A … : Low coolant light comes on when AC, defrost or heater is on, but only if the car is in gear and stopped, what’s wrong with my car?

When I turn on my AC the radiator fans do not turn on. The fans do come on when the car warms up so I know they are working and the fuses are good. The AC compressor does come on and the air blows ice cold when the car is moving. Car is a 2006 Chrysler Sebring Sedan 2.7l v6.
ANSWER : The control circuit for the fans needs to be checked. For example, there is usually a condenser fan relay in the A/C electrical controls. There could be a fault with that relay and/or wiring problems, perhaps even just a loose connection, blown or loose fuse, and so forth. To resolve something like this, the recommended service is an electrical component diagnostic. If you request that diagnostic service, the responding certified mechanic will get the problem pinpointed and resolved. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

Read Full Q/A … : Low coolant light comes on when AC, defrost or heater is on, but only if the car is in gear and stopped, what’s wrong with my car?

My engine coolant light is coming on and after hitting a pot hole my thermostat light pops on, and after a few miles car run hot
ANSWER : Hi there. It is quite possible that you may have damaged the radiator when hitting the pot hole. Although there are protective shields located under the radiator itself, they are typically very thin and made of plastic in most cases. Sometimes the quick impact can cause cracking along the base of the radiator. When this happens, coolant will leak rather quickly. I would recommend two things, first, stop driving the vehicle until this issue is repaired. Second, contact a professional mobile mechanic to complete a coolant leak inspection so they can pinpoint precisely what is causing the leak and what repairs will be needed. This will allow you to have an accurate estimate for repairs.

Read Full Q/A … : Low coolant light comes on when AC, defrost or heater is on, but only if the car is in gear and stopped, what’s wrong with my car?

Car won’t start. The check engine light, battery light, and oil change light are coming on. I tried jumping the car and nothing happened. Why won’t my car start?
ANSWER : Hi and thanks for contacting Your Mechanic. If sometimes your vehicle will start with the new alternator and sometimes it won’t, then there is a loose connection in your charging system. Check all of the wires to the alternator and to the battery. Make sure that the battery cables are clean and tight. Make sure that the wires to the starter are clean and tight. A loose ground to the ignition system will cause the vehicle to not crank over. Check all of the ground wires from the battery to the starter. Make sure that they are clean and tight. If you need further assistance troubleshooting your no start situation, then seek out a technician, such as one from Your Mechanic, that can assist you.

Read Full Q/A … : Low coolant light comes on when AC, defrost or heater is on, but only if the car is in gear and stopped, what’s wrong with my car?

Battery and oil light come on when trying to start car, take keys out try again car starts no problem and lights go away
ANSWER : Of course, don’t switch gears without being fully stopped, unless your Owner’s Manual or the manufacturer has alternative advice. However, the gear shift issue has no relation to the no-start problem you are describing. Inasmuch as you only have 6,000 miles on the car, the "constant on and off" that you believe has occurred is meaningless in comparison to the expected total vehicle service life. That is, assume what you perceive as "constant on and off", during merely 6,000 miles, might be equivalent to using the car "normally" for three years. A new car should be trouble free for at least 5 years, unless there is a defect, so your "constant on and off" is not a causal factor for any fault on the vehicle. What you might have is a defect in the ignition switch, or perhaps the immobilizer system, but if the problem is not in the switch itself, clearly there is an electrical problem.

If your vehicle is under warranty, by law the dealer MUST repair the issue you are describing within a prescribed time frame and number of "attempts", otherwise the dealer will run afoul of Federal and state Lemon Laws that give you very specific rights, and recourse (contact an Attorney; we are Mechanics, NOT attorneys). Consequently, if the vehicle is still under warranty, to save yourself money do be sure to seek a resolution from the dealer. If the vehicle is not under warranty, obviously a certified Mechanic from YourMechanic could identify the electrical fault and resolve this for you. If you want to go that route, please simply request a no start diagnostic -electrical system and the responding certified mechanic will get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

Read Full Q/A … : Low coolant light comes on when AC, defrost or heater is on, but only if the car is in gear and stopped, what’s wrong with my car?

Engine Light and AT light. Car goes into limp mode
ANSWER : Hello. Most of the time this is the result of a transmission failure. It is common for this transmission to have internal pressure problem which will cause these codes. It can also be a voltage problem so I always check that first. I check the voltage going to the transmission and if it is too low I repair that issue which is commonly the ignition switch. If the voltage is fine, then the transmission pressures need to be checked and it will more than likely need to be replaced. I would have a transmission specialist look into this.

Read Full Q/A … : Low coolant light comes on when AC, defrost or heater is on, but only if the car is in gear and stopped, what’s wrong with my car?

When the stop engine oil low light keep coming on I put oil in the car why does it keep coming on
ANSWER : Hi there. From the description you have provided, your vehicle’s low oil light comes on when the engine is stopped; this may not be a low oil level. It is very important to not overfill the engine with oil. Always check the level using the dipstick before adding oil. The best time to check the level is at operating temperature, engine off, on level ground, and after the car has sat for at least 5 minutes allowing oil to return to the oil pan. The level should be between ’add’ and ’full’ on the dipstick (1 qt range). This could be a symptom of a faulty oil level sensor. It could be a poor electrical connection at the oil level sensor. It could also be a fault in the IPC (instrument panel cluster). I recommend having your vehicle’s oil low light keeps coming on diagnosed and repaired by a certified technician, such as one from YourMechanic.

Read Full Q/A … : Low coolant light comes on when AC, defrost or heater is on, but only if the car is in gear and stopped, what’s wrong with my car?

Eric smoalih

I am a certified master technician with the National Institute for Automotive Service Excellence (ASE), and I have been working as an auto mechanic for over 15 years. I am passionate about my work, and I take great pride in helping people keep their cars running smoothly.