1. Oxygen Sensors

Oxygen sensors, or O2 sensors, keep tabs on the oxygen levels in exhaust gases before and after they leave the tailpipe. They send this info to the vehicle’s electronic control unit (ECU), which tweaks the air-fuel mix for a smooth ride. Most cars have two O2 sensors per exhaust pipe—one before and one after the catalytic converter.

If an O2 sensor fails, fuel economy could drop by up to 20%. Keep an eye out for black smoke, a sulfur smell, or engine hiccups.

2. Mass Airflow Sensor

The mass airflow sensor (MAF) is crucial for the fuel injection system, measuring the air entering the engine. This data helps the ECU decide how much fuel to inject for optimal combustion. Typically, it’s located between the air filter and the intake plenum.

If the MAF sensor goes bad, expect rough starts, stalling, or sluggish acceleration.

3. Engine Oil Level Sensor

Running low on oil can lead to some serious engine drama. Luckily, modern cars come with an engine oil level sensor that warns drivers when oil levels dip too low. This sensor usually sits on the oil pan, visible from beneath the vehicle.

Signs of a faulty sensor include incorrect oil level readings and a flickering oil light on the dashboard.

4. Engine Oil Pressure Sensor

The oil pressure sensor alerts the ECU if the oil pressure drops below the safe zone. If it does, engine parts might not get enough oil, leading to wear and tear. Typically found near the engine block, symptoms of a faulty sensor include a warning light and strange noises from the engine.

5. Coolant Temperature Sensor

The coolant temperature sensor (CTS) keeps an eye on the engine’s coolant temperature. If it fails, it can send wrong signals to the ECU, causing overheating. Usually located near the thermostat housing, signs of trouble include overheating and poor fuel efficiency.

6. Throttle Position Sensor

The throttle position sensor (TPS) measures how far the throttle valve opens, letting more air into the engine. It’s usually found inside the throttle body. If the TPS fails, expect rough idling or stalling.

7. Intake Air Temperature Sensor

This sensor measures the temperature of the air entering the engine. It helps the ECU adjust the air-fuel mix. Typically located between the air filter and intake manifold, a bad IAT sensor can lead to poor acceleration and rough idling.

8. Coolant Level Sensor

The coolant level sensor checks the antifreeze level in the engine. If it drops too low, the ECU sends a warning. Usually found in the radiator or expansion tank, a faulty sensor might keep the warning light on even if coolant levels are fine.

9. Manifold Absolute Pressure (MAP) Sensor

The MAP sensor measures the pressure in the intake manifold, helping the ECU calculate air density for better performance. Typically located on the intake manifold, signs of a bad MAP sensor include reduced power and poor fuel economy.

10. Boost Pressure Sensor

11. Crankshaft/Camshaft Position Sensor

These sensors track the positions of the crankshaft and camshaft, crucial for engine timing. If they fail, expect startup issues and erratic acceleration.

12. NOx Sensor

Common in diesel engines, the NOx sensor measures nitrogen oxide emissions. If it fails, fuel economy and engine power can take a hit.

13. Fuel Temperature Sensor

This sensor tracks the temperature of the fuel, helping the ECU manage fuel injection. A faulty sensor can lead to poor performance and overheating.

14. Engine Knock Sensor

The knock sensor detects vibrations from the engine, helping the ECU adjust ignition timing. If it fails, power and fuel efficiency can drop, and knocking sounds may occur.

15. Fuel Pressure Sensor

Last but not least, the fuel pressure sensor monitors the pressure in the fuel rail. If it’s not working right, the engine might not get enough fuel, leading to stalls and poor performance.