Car Sensor Problems? 11 Common Problems & Solutions

Modern cars have multiple sensors spread throughout the car to optimize performance, maximize fuel efficiency, and maintain safety.

Each car may have upwards of 70 or more sensors monitoring performance, but many of them will never need to be replaced.

Of those that will need to be replaced, we’ve gathered the most common problematic sensors that you may need to diagnose and replace over the lifetime of your car.

#1 – Coolant Temperature Sensor

The coolant temperature sensor measures the engine temperature and relays that information to the engine control unit (ECU) and possibly a temperature gauge in the gauge cluster.

The ECU monitors the temperature to adjust the air-fuel ratio as the engine warms up to operating temperature, and it can also shut off the engine if it detects the temperature approaching a level that will damage the engine or other components.

How to Fix It

Coolant temperature sensors operate within a set range of resistance. That resistance will change based on temperature, and the ECU will use the resistance to measure a change in voltage through the sensor.

You can use a multi-meter to measure voltage in and out of the sensor and to measure the exact resistance of the sensor to determine if the sensor has gone bad.

A bad sensor may prevent the car from starting or idling when the engine is cold, and it can also give a false reading to the gauges you see inside the car.

Most coolant temperature sensors are threaded into the intake manifold or a cylinder head where the end is submerged in coolant. Only change the sensor when the engine is cold to prevent pressure from spraying hot coolant on the engine and you.

#2 – Coolant Level Sensor

Your engine uses coolant circulated through the cooling system to stay within a pre-determined operating temperature range.

The coolant level sensor indicates when the amount of coolant in the system is below a minimum threshold in the coolant reservoir or overflow reservoir.

How to Fix It

The coolant level sensor is connected to the coolant/overflow reservoir and should illuminate a light in the gauge cluster when the amount is low.

In a worst-case scenario, the sensor triggers a safety protocol in the engine control unit to prevent the engine from running and overheating.

The sensor is easy to replace with a new one and should be done when the engine (and coolant) is cold. This will prevent spraying hot coolant on your car and you.

#3 – Engine Oil Pressure Sensor

The engine oil pressure sensor measures the oil pressure after the oil pump. It can be next to the intake manifold or threaded into the engine block.

Most sensors are made from metal and plastic, both of which can fatigue and fail.

When the sensors fail, they often trigger a safety setting to shut the engine off because the engine control unit may think the engine is in danger of being damaged.

How to Fix It

Most oil pressure sensors are monitored by the engine control unit. They may also be connected to a gauge in the gauge cluster to give the driver a visual readout for monitoring.

When the sensors fail, the ECU may shut the engine off and the gauge may show the minimum (usually 0) or maximum pressure allowed.

The sensor can be disconnected from the wiring connector and threaded out of the engine block when the engine is cold. A replacement sensor can be threaded in its place, the wiring harness reconnected, and then you can start the engine to verify the replacement sensor works.

#4 – Engine Oil Level Sensor

One sensor most cars have will be the oil level sensor. It measures the amount of oil in the oil pan at the bottom of the engine to ensure you have a minimum amount of oil to safely run the engine.

When the oil level drops below the sensor, it will illuminate a light in your gauge cluster to alert you that the oil level is low.

Some cars may have two separate oil level sensors: one for a low oil level indicator, and the second to prevent the engine from starting when the amount of oil is at an unsafe level.

How to Fix It

The oil level sensors will be attached to the side of the oil pan on the bottom of your engine. You may find one or two on the oil pan, oftentimes on opposite sides of the pan to prevent mixing the wiring connectors.

If the low-level sensor fails, it will often indicate a low level of oil in the engine when the engine is full of oil. If the unsafe level sensor fails, it will often prevent the engine from starting when there is enough oil in the engine.

The low indicator light will often not illuminate, which suggests only the unsafe sensor has failed. Both can be removed from the oil pan with basic tools and replaced with a new sensor.

#5 – Exhaust System Oxygen Sensor

Oxygen sensors (also called O2 sensors) measure the air-fuel ratio in the exhaust gas after the combustion process. There are typically two separate sensors per cylinder bank that measure the gas pre-catalytic converter and post-catalytic converter.

The engine control unit compares the values between the sensors to determine if the catalytic converter is reducing the exhaust emissions.

If the sensors need to be replaced, the incorrect values could cause the computer to change the fuel mixture.

How to Fix It

The oxygen sensors are closely monitored by the engine control unit and will cause the check engine light (CEL) to illuminate if a problem is detected.

Most diagnostic computers can check each sensor individually and notify you which sensor is out of the manufacturer’s range.

O2 sensors should be replaced around the 75,000 – 100,000-mile mark if not before, and they just thread into the exhaust piping. It is recommended to replace all of them as a set at the 75,000-mile mark.

#6 – Camshaft And Crankshaft Position Sensors

The engine control unit (ECU) uses sensors to monitor where the crankshaft and camshaft(s) are in their rotations and compares these values to adjust combustion timing for maximum power and to reduce emissions.

If one sensor fails, the computer should illuminate the check engine light (CEL) and default to a basic timing program without adjusting the timing.

How to Fix It

Your car may or may not start if one of these sensors fails. If it does start, it may take a longer time to initially start, and the engine may run rough because the computer isn’t receiving the information it needs from all sensors.

A diagnostic scanner can verify which sensor has failed, and you can replace the sensor individually with simple hand tools. Each sensor should be attached to the engine with one or two fasteners.

#7 – Engine Knock Sensor

Your engine has knock sensors to detect pre-ignition (also called detonation) and will adjust the combustion timing to prevent engine damage.

If this sensor fails it can cause the engine control unit to adjust timing until the engine goes into “limp mode”. This will reduce engine power and may prevent you from driving the car until the sensor is replaced.

How to Fix It

The knock sensors are attached to the side of the engine block with one or two fasteners. They can be replaced with basic hand tools such as a socket and ratchet but be careful not to drop the sensor.

It is very delicate and can be damaged with a simple impact.

#8 – Fuel Level Sensor

The fuel level sensor reads how much fuel is in your fuel tank and your fuel gauge is the visual indication of that reading as you drive.

If the sensor fails, your fuel gauge will read incorrectly. It may always show a full or empty tank if the sensor fails.

How to Fix It

The fuel level sensor is located inside the fuel tank. You may need to remove the fuel tank from the car to remove the sensor unless there is an opening in the car floor with access to the top of the fuel tank.

The sensor can be removed and replaced easily, and a new sensor should restore the accuracy of your fuel gauge.

#9 – Fuel Pressure Sensor

The fuel pressure sensor measures the fuel pressure in the fuel pressure line coming from the fuel tank. The sensor is typically attached to the fuel pressure rail for easy access and replacement.

The engine control unit (ECU) uses the sensor information to modulate line pressure and adjust the air-fuel ratio in the combustion process.

How to Fix It

A faulty fuel pressure sensor may cause the engine control unit to add extra fuel to the combustion process.

This extra fuel will reduce your fuel mileage, but it can damage the spark plugs and catalytic converters that are continuously soaked in extra fuel.

The sensor can be removed and replaced but do it after the car has sat for a minimum of 15 minutes or more. This will reduce the pressure in the fuel line and prevent pressurized fuel from being sprayed on you and your car.

#10 – Mass Airflow (MAF) Sensor

The mass airflow (MAF) sensor measures the amount of air entering the engine, and your engine control unit adjusts the fuel amount injected in the combustion process to achieve the optimum air-fuel ratio.

If the MAF sensor sends incorrect information, the engine may stumble and fail to idle.

How to Fix It

The MAF sensor will be located on the intake ducting between the intake manifold and the air filter housing.

It can become dirty, and cleaning it requires the removal of the sensor and screen. The sensor is held to the ducting by small fasteners and can be removed with simple tools.

Try cleaning the sensor and screen before completely replacing it.

#11 – Manifold Absolute Pressure (MAP) Sensor

Your fuel injection system may have an additional sensor to measure incoming air going to the engine.

The manifold absolute pressure (MAP) sensor measures pressure in the intake manifold to optimize the air-fuel mixture for maximum performance.

How to Fix It

The MAP sensor is commonly used in factory turbocharged intake systems as it measures the boost pressure the turbocharger is supplying to the engine.

If the sensor fails, the engine control unit will incorrectly adjust the air-fuel mixture and may reduce power output.

The sensor is located on the intake manifold and can easily be replaced with basic hand tools.

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