Symptoms of a Bad or Failing Low Water Sensor

Low water sensors are more commonly known, or referred to, as coolant level sensors. The purpose of these sensors is to alert the driver of low coolant level in the engine cooling system. When coolant level in the engine is low, the cooling system cannot adequately remove excess heat from the engine. This causes the engine to overheat which will lead to eventual engine failure. The most common results of engine overheating include warped or cracked cylinder heads, and blown head gaskets.

Normal operation

The typical coolant level sensor has two probes that, when inserted into engine coolant, pass electricity between them. This creates a complete electrical circuit. When coolant level falls below the probes, the circuit is broken and the low coolant level warning lamp is illuminated. This alerts the driver to have the cooling system checked.

There are basically two symptoms of a failed coolant level sensor.

Low Coolant Warning Light always on

Since the Low Coolant Warning Light is illuminated when the lamp circuit is electrically open, the sensor could go open internally regardless of actual coolant level. This would cause the coolant light to always be on. The necessary repair here would be to replace the sensor.

Low Coolant Warning Light does not illuminate on low level

If the coolant level sensor is electrically shorted internally, the coolant level circuit will never go open when coolant level falls too low. This prevents the Coolant Level Warning Light from illuminating and alerting the driver to a potentially hazardous situation. If the cooling system isn’t checked on a regular basis, engine damage may occur.

Have a trained technician like those at YourMechanic diagnose the condition. If the sensor needs replacement, they can do that. If another issue is the cause, they can fix that, too.


Next Step

Schedule Vehicle Engine Cooling Inspection

The most popular service booked by readers of this article is Vehicle Engine Cooling Inspection. Once the problem has been diagnosed, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. YourMechanic’s technicians bring the dealership to you by performing this job at your home or office 7-days a week between 7AM-9PM. We currently cover over 2,000 cities and have 100k+ 5-star reviews... LEARN MORE

SEE PRICING & SCHEDULING

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Recent Vehicle Engine Cooling Inspection reviews

Excellent Rating

(191,118)

Rating Summary
179,680
6,078
1,268
920
3,172
179,680
6,078
1,268
920
3,172

Matthew

34 years of experience
1438 reviews
Matthew
34 years of experience
Hyundai Elantra L4-1.8L - Air Filter - Hampton, Virginia
This is the 3rd time that Matt has had my service calls. He’s the consummate professional. He always shows up on time or earlier than the appointment time and he gets right to work. He’s also quite personable. I’d recommend his services and I wouldn’t hesitate to refer him to anyone that I know!
GMC C1500 - Ignition Ignitor - Hampton, Virginia
best mechanic ever friendly

Nathan

22 years of experience
298 reviews
Nathan
22 years of experience
Honda Accord V6-3.5L - Oil Change - Austin, Texas
The service was fast and super convenient. He was extremely friendly and had an answer to all my questions.
Chevrolet Silverado 1500 - Windshield Wiper/Washer System Inspection - Austin, Texas
He was timely, thorough and informative.

William

35 years of experience
731 reviews
William
35 years of experience
Mazda 3 L4-2.0L - Vehicle Engine Cooling Inspection - Phoenix, Arizona
Earlier than expected! Diagnosed car within an hour and had an estimate for repairs quick

Glenn

22 years of experience
38 reviews
Glenn
22 years of experience
Pontiac Grand Prix V6-3.8L Turbo - Vehicle Engine Cooling Inspection - Indianapolis, Indiana
Ok

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

Related articles

How to Replace a Coolant Temperature Sensor
The coolant temperature sensor switch is not working if the engine emits black smoke. The switch may have failed if the car gets poor fuel economy.
How to Replace a Brake Booster Vacuum Sensor
The brake booster vacuum pressure sensor is a vital part of power brake operation. A Check Engine Light or a hard brake pedal are signs of failure.
How to Replace an Exhaust Gas Recirculation (EGR) Temperature Sensor
Exhaust gas recirculation (EGR) temperature sensors monitor the EGR cooler's operation. One is on the exhaust manifold and one is near the EGR valve.

Related questions

Air conditioning blockage pressure - 1988 Mercedes-Benz 300TE
Hey there. The condenser is blocked or the expansion valve is stuck causing the problem. Make sure when testing you have proper air flow across the condenser. If the fan clutch is not working good then the pressures will be...
Where is the camshaft sensor position A in a 2008 Honda Odyssey 3.5L V6 engine?
Facing the motor in the van you will find the sensor in the front of the rear of the cylinder head. That would be passenger side of the rear head. Mounted in the end of the head.
Still overheating after replace radiator
Certain engine faults, such as a leaking head gasket(s) or poor engine running condition can cause overheating. If bubbles are coming up in the coolant, you should test for exhaust in the coolant. If present, that would suggest either a...

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1 (855) 347-2779 · hi@yourmechanic.com