Can Low Coolant Cause Check Engine Light? Fixing Tips

The check engine light (or CEL) activates to alert oblivious drivers of any potential issue inside the engine.

Meanwhile, coolant is an engine liquid added to balance its internal temperature and control the heat.

Hence, here comes the important question: can low coolant cause check engine light? My guide will dig deep into the possible relationship between the two; keep scrolling.

Can Low Coolant Cause Check Engine Light? 

can low coolant cause check engine light

Yes. When the coolant amount within your radiators runs too low, the engine compartments will overheat sooner or later, prompting the light to flash and send overheating messages.

Long story short: the CEL is not triggered by the coolant levels themselves – but rather by the engine overheats that result from low coolant! 

And even when the overheating has not yet occurred, the fact that the temperature regulation does not function as well as it used to is more than enough to alert the coolant sensors.

They will send false readings to your car computer immediately.

Although the computer can detect issues within the coolant systems, it cannot read the voltage signals at all – and hence, fail to sustain constant communication with the coolant sensors.

No wonder the CEL is forced to light up! 

On another note, do not mistake the check engine lights for the coolant engine light:

  • CEL can be triggered by many issues, not just the low coolant amounts
  • Many car vehicles only have the CEL and not the coolant check engine light
  • Low coolant issues do not always trigger the CEL – unless they cause engine damage serious enough (ex: overheat conditions) that force the CEL to illuminate.

How to Fix Low Coolant Symptoms To Turn Off The Check Engine Light?

will low coolant cause check engine light

Wait until the engine components have cooled down, then remove the coolant caps and drain all the old coolants off the tank.

Create the coolant mixture according to your manufacturer’s recommendation (an antifreeze- water ratio of 50:50 or 70:30) and pour it into the tank.

Once done, drive the car for a little while and check the coolant levels again.

Keep an eye out for possible leakage holes and have them properly patched; otherwise, the coolant will end up dripping off the tank!

My full guide is as below: 

Step 1. Gather The Necessary Tool

To add coolants to the reservoir, you obviously need antifreeze and water (commercial premixed solutions bought at shops are also great).

And do not forget your jack stands, car’s manual, and protective clothing for possible burning injuries.

Step 2. Turn Off Your Vehicle And Wait For The Engine To Cool Down

Wait until your engine has gone completely cool to prevent severe scalding.

The process might take 5 to 30 minutes depending on the surrounding temperature and usage history (ex: has the car been idle for days or just recently used?)

Step 3. Find Your Coolant Reservoir or Radiator

On most cars, the reservoir has a translucent color with black or metal screw-on lids, accompanied by a hose connected to the radiators.

You should find them at the front of the engine (behind the grills) with the marked fill range on the side.

To learn where exactly the radiator/reservoir lies, it would be best to consult your service manuals for guidelines and directions.

Step 4. Pull Off The Coolant Cap 

Now open your car hood to locate the coolant cap, which usually looks much more popping/outstanding than any other circular cap within the engine bays.

Not to mention, some modern car models even provide clear labels for the caps, making them even easier to locate! Once spotting the coolant cap, start removing it completely – but before you do so: 

  • Ensure the coolant caps are not hot. If they burn under your hand, do not open them; the scalding fluid and pressured gas may spiral out and leave severe burns on your skin! 
  • When the engine cools down a bit, loosen the reservoir cap gradually to help release the trapped pressure. Open it bit by bit; do not do so abruptly.
  • Use a thick cloth or rag for better safety when you finally unscrew the cap. Also, safety goggles and gloves are highly recommended (even when your engine stays cool) to sidestep injuries.

What if the coolant caps are too tight? Press on them when twisting to help them loosen. I also suggest using small rubber mats below the cloth to gain a better grip.

Step 5 (optional). Drain Your Old Coolant

Most of the time, refills are enough to turn the coolant level to its required number. There is no need to drain the old ones – unless they are contaminated or contain the wrong antifreeze-water ratio.

If your car does need complete coolant drains, follow the steps given here: 

  • Raise your car with a jack stand and support its front end. Next, place a big oil pan/ drain pan/ disposable pail/ bucket under the radiators.
  • Remove the pressure/radiator caps off your coolant tanks. Locate the drain cock and unscrew it according to the manuals. Since drain cocks are divided into several styles (quarter-pull-and-turn, quarter-twist, and screw threads), remember to read the guidelines carefully.
  • Remove the engine hose and radiator clamp; if your clamps are spring-style, use a slip-joint plier to pull them from the necks.
  • Drain the remaining engine coolant. Once done, return the radiator hoses and drain cocks to their places.

Step 6. Create The Coolant Mixture

A popular assumption is that coolant and antifreeze are identical, but that is not the case at all. Long story short:

  • Coolant: Comprising both antifreeze and water in the recommended ratio
  • Antifreeze: one of the main coolant ingredients (besides water)

Although antifreeze alone can absorb and disperse excessive heat, a well-made coolant mixture still proves to be much more potent.

So either make your own water-antifreeze mixture (50:50 or 30:70) or purchase premixed solutions at automobile stores or retail establishments.

Certain brands also required extended life coolants for their vehicle models – which you may not find in local auto stocks.

Buy them from dealers instead; do not resort to cheaper alternative products that don’t fit the car’s demands at all.

Step 7. Add The Coolant Into The Tank

Before proceeding, do not forget to check the MIN (minimum) and MAX (maximum) lines on the reservoir or overflow tank.

They indicate where the coolant levels currently are: anything near or below MIN means extra coolants will be needed.

  • You may use distilled water or diluted coolants in emergencies. However, they should be considered the last resort; replace them immediately when resources are available.
  • The best way to add coolant is via the coolant tanks instead of the radiator. Still, the latter can be accepted if your car is a classic, older model with no overflow tank (provided your engine has cooled down already). Fill the radiators slowly until the coolant reaches one inch underneath the radiator’s neck.
  • Always use funnels to keep spillage at bay. That way, the coolant never spills onto the floor or clings to your skin. Keep in mind how dangerous this substance can be, and take extra caution every step of the way.

Step 8. Wait Before Driving

  • If you add coolant before driving:

Once adding the coolants with my steps above, close the car’s hood and start your engine.

Keep it running until the dash’s cooling/heating gauge reaches standard operating temp – which should only take a few minutes.

  • If you add engine coolants after driving: 

How long you should wait depends on the current season, the time spent driving on the street, and your driving speed.

For instance, a short drive to a nearby 24/7 store requires 20 to 30 minutes of waiting; meanwhile, motorway passing at 70 MPH means your vehicle needs at least 1 hour to rest.

Plus, colder climates shorten your waiting time – while long summer increases it.

Step 9. Check Your Engine Coolant Levels Again. Look For External Coolant Leaks

After taking the car out for test rides and giving the engine enough cooling time, it does not hurt to re-confirm your level of coolant again.

Plus, you should always look for leaks and faulty water pumps before, during, and after the coolant fills.

There is no point adding as much coolant as possible into the tank if it eventually blows out through the leakage hole anyway!

Why Is Your Check Engine Light Still On After Filling Coolant?

coolant low check engine light

Does low coolant cause check engine light? Yes, but after the new flow of coolant, the light still refuses to turn off; what happened? Then one of the scenarios below must have happened to your car:

  • Your check engine light coolant thermostats are stuck open
  • The check coolant temperature sensors are at fault
  • Other issues are behind the activated CEL 

For the first two (stuck thermostats and faulty sensors), your only job is to have them replaced. But the last scenario is much more serious. 

Activated CELs and low coolant fluids happening simultaneously lead to the common belief that the latter triggers the former – but that is not always the case.

The CEL blinking may stem from numerous other reasons, too, so use a scanning tool to read its error codes and get down to the root of the problem.

How Often Should You Check The Engine Light Coolant?

Coolants are obviously a very critical part of the engine, so I suggest checking them at least once per month – or whenever you drive to the gas station for gas fills.

Using premium/ higher-end coolants would also reduce the need to inspect them too often. Do not hold back on your investments! 


Can low coolant cause check engine light? Yes, if it causes severe engine issues that might trigger the warning light, such as overheating or wrong data readings.

Add the coolant according to my guidelines to turn the low coolant check engine light off.

If you struggle with any part of the process, or the light is still turned on after the coolant fills, write to me for more expert advice.

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