What is an Oxygen Sensor and what does it do?

An Oxygen Sensor, also called a Lambda Sensor, is fitted in the exhaust pipe of a petrol engine to measure how much unburned oxygen is left in the exhaust gases. It sends this reading continuously to the Engine Control Unit (ECU), which uses it to fine-tune the air-fuel mixture for the best balance of performance, fuel economy, and low emissions. A faulty Oxygen Sensor is one of the most common reasons for poor mileage and a lit 'Check Engine' light.

What is a Mass Air Flow (MAF) Sensor?

The Mass Air Flow Sensor is mounted between the air filter and the throttle body, and it measures the exact amount of air entering the engine at any moment. The ECU uses this reading to calculate precisely how much fuel to inject to match that air, keeping the air-fuel ratio correct under all driving conditions. Without an accurate MAF reading, the engine can run too rich or too lean, causing rough idling, poor power, or higher fuel consumption.

What is a Manifold Absolute Pressure (MAP) Sensor?

The MAP sensor is fitted on the intake manifold and measures the air pressure (vacuum) inside it, which changes depending on engine load and throttle opening. Many petrol vehicles use this pressure reading, along with engine speed, to estimate the amount of air entering the cylinders and calculate the correct fuel quantity — this is called 'speed-density' fuel injection. It also helps the ECU adjust ignition timing correctly as driving conditions change, such as going uphill or accelerating hard.

What is a Throttle Position Sensor (TPS)?

The Throttle Position Sensor is mounted on the throttle body and tells the ECU exactly how far the throttle valve is open at any moment — in other words, how much the driver is pressing the accelerator. The ECU combines this with other sensor data to decide fuel injection quantity, ignition timing, and gear shift points in automatic transmissions. A faulty TPS often causes hesitation, jerky acceleration, or an unstable idle speed.

What is a Crankshaft Position Sensor (CKP)?

The Crankshaft Position Sensor detects the exact position and rotational speed (RPM) of the engine's crankshaft, usually by reading teeth on a toothed wheel attached to it. This information is critical for the ECU to time the fuel injection and spark ignition precisely for each cylinder. If this sensor fails, the engine typically will not start at all, since the ECU has no way of knowing where each piston is.

What is a Camshaft Position Sensor (CMP)?

The Camshaft Position Sensor monitors the rotation and position of the camshaft, which controls the opening and closing of the intake and exhaust valves. Working together with the Crankshaft Position Sensor, it tells the ECU exactly which cylinder is on its intake or power stroke, allowing sequential fuel injection and precise ignition timing for each cylinder individually. It also enables features like Variable Valve Timing found in many modern petrol engines.

What is an Engine Coolant Temperature Sensor (ECT)?

The Engine Coolant Temperature Sensor is fitted in the engine's cooling passage and measures the temperature of the coolant circulating through the engine block. The ECU uses this reading to enrich the fuel mixture during cold starts, control the cooling fan, and adjust ignition timing based on engine temperature. It is also the main source of the temperature reading shown on the dashboard gauge, and a faulty sensor can cause overheating warnings or poor cold-start performance.

What is an Intake Air Temperature Sensor (IAT)?

The Intake Air Temperature Sensor measures the temperature of the air entering the engine, since cold air is denser and contains more oxygen than hot air. The ECU uses this reading, along with the airflow measurement, to fine-tune the exact amount of fuel needed for a correct air-fuel mixture in every season and driving condition. It also helps the ECU adjust ignition timing to prevent engine knock when intake air is very hot.

What is a Knock Sensor?

A Knock Sensor is mounted on the engine block and detects the vibration pattern caused by 'engine knock' or 'pinging' — abnormal, uncontrolled combustion inside the cylinders that can seriously damage an engine over time. As soon as it senses this vibration signature, it alerts the ECU, which immediately retards the ignition timing slightly to stop the knocking. This protects the engine and allows it to safely run on a range of petrol fuel qualities.

What is an Engine Oil Pressure Sensor?

The Engine Oil Pressure Sensor is screwed into the engine block or oil filter housing and continuously measures the pressure of the lubricating oil being pumped through the engine's moving parts. If oil pressure drops too low — due to a leak, a failing oil pump, or very low oil level — the sensor immediately triggers the oil pressure warning light on the dashboard. Ignoring this warning can lead to severe engine damage within minutes, since parts inside the engine can seize without proper lubrication.

What is an Engine Oil Level Sensor?

The Engine Oil Level Sensor sits inside the oil pan (sump) and measures how much oil is currently present in the engine, unlike the oil pressure sensor which measures flow pressure. Many modern petrol cars use this sensor to warn the driver on the dashboard if the oil level drops below the safe minimum, without needing to check the dipstick manually. This early warning helps prevent engine damage caused by running with insufficient oil.

What is a Fuel Level Sensor?

The Fuel Level Sensor sits inside the fuel tank, usually attached to a float that rises and falls with the fuel level, connected to a variable resistor. As the float moves, the resistance changes, and this change is converted into the fuel gauge reading shown on the dashboard. This is the sensor responsible for warning the driver with a low-fuel light when the tank is nearly empty.

What is a Fuel Pressure Sensor?

The Fuel Pressure Sensor is fitted on the fuel rail or fuel line and continuously measures the pressure at which petrol is being delivered to the fuel injectors. Modern fuel-injected engines need very precise fuel pressure for the injectors to spray the correct amount of fuel at the correct time. If pressure is too low or too high, the ECU adjusts the fuel pump accordingly, and a failing sensor can cause hard starting, poor acceleration, or stalling.

What is a Turbocharger Boost Pressure Sensor?

In turbocharged petrol engines, the Boost Pressure Sensor measures the extra air pressure created by the turbocharger as it forces more air into the engine than it could draw in naturally. The ECU uses this reading to control the turbo's wastegate and adjust fuel injection to match the extra air, ensuring maximum power is delivered safely without over-boosting, which could damage the engine. It is essential for the performance and reliability of any turbo-petrol vehicle.

What is an EGR Position Sensor?

The EGR (Exhaust Gas Recirculation) Position Sensor monitors exactly how far the EGR valve is open. This valve recirculates a small, controlled amount of exhaust gas back into the intake to lower combustion temperature, which reduces harmful NOx emissions. The sensor reports the valve's actual position back to the ECU, which then makes fine adjustments to keep emissions within limits without hurting engine performance.

What is a Vehicle Speed Sensor (VSS)?

The Vehicle Speed Sensor, usually mounted on the transmission or gearbox output shaft, measures how fast the vehicle is actually moving. This reading is used for the speedometer display, for shift timing in automatic transmissions, for cruise control, and by the ECU to adjust idle speed and fuel delivery when the vehicle is moving versus stationary. A faulty VSS can cause an inaccurate speedometer, harsh gear shifts, or a non-functional cruise control.

What is a Wheel Speed Sensor (ABS Sensor)?

A Wheel Speed Sensor is fitted at each wheel hub and continuously measures how fast that individual wheel is rotating. The Anti-lock Braking System (ABS) module compares the speed of all four wheels, and if it detects one wheel slowing down much faster than the others — a sign it is about to lock up under hard braking — it rapidly pulses the brake pressure at that wheel to prevent skidding. This same sensor data is also used by traction control and electronic stability control systems.

What is an Airbag Crash Impact Sensor (SRS)?

Airbag Crash Impact Sensors are placed at the front, sides, and sometimes rear of the vehicle, and they detect sudden, severe deceleration caused by a collision. Within milliseconds of detecting an impact strong enough to be a real crash, these sensors signal the Supplemental Restraint System (SRS) control unit, which instantly fires the airbags and, in many vehicles, also tightens the seat belt pretensioners. Getting the sensor's sensitivity right is critical — it must trigger during a real crash but never during normal driving, like hitting a pothole.

What is a Seat Belt Buckle Sensor?

The Seat Belt Buckle Sensor is built into the seat belt buckle and detects whether the belt has been properly fastened. If the driver or a front passenger starts the vehicle or drives without buckling up, this sensor triggers the seat belt reminder chime and warning light on the dashboard. In many modern cars, this same sensor also communicates with the airbag control unit, since seat belt status affects how the airbag system deploys in a crash.

What is a Steering Angle Sensor?

The Steering Angle Sensor is mounted on the steering column and measures how far, and in which direction, the driver has turned the steering wheel, along with how quickly it is being turned. This information is used by Electronic Stability Control to compare the direction the driver intends to go with the direction the car is actually moving, and by electric power steering systems to adjust assist levels. It is also used by some vehicles to adjust headlight direction while cornering.

What is a Yaw Rate and Lateral Acceleration Sensor?

The Yaw Rate Sensor measures how fast the vehicle is rotating around its vertical axis — in simple terms, how quickly it is spinning or turning — while the Lateral Acceleration Sensor measures sideways forces, such as during hard cornering. Together, usually combined in a single unit, they are core inputs for Electronic Stability Control (ESC), which compares this actual motion with what the steering angle suggests the driver intends, and automatically applies individual brakes to help correct a skid.

What is a Brake Pedal Position Sensor?

The Brake Pedal Position Sensor detects when, and often how far, the driver has pressed the brake pedal. At its simplest, this switches on the brake lights, but in modern vehicles it also signals systems like cruise control (to disengage it), brake assist (to add extra braking force in an emergency stop), and start-stop systems (to know when it's safe to restart the engine). It plays a direct role in overall vehicle safety.

What is an Accelerator Pedal Position Sensor?

In modern petrol vehicles with 'drive-by-wire' throttle systems, the Accelerator Pedal Position Sensor replaces the old mechanical cable, electronically measuring exactly how far the driver has pressed the accelerator pedal. This signal is sent to the ECU, which then electronically opens the throttle body by the appropriate amount, after factoring in other conditions like cruise control, traction control, or engine protection. This allows for smoother, computer-optimized throttle response compared to a purely mechanical link.

What is a Clutch Position Sensor?

The Clutch Position Sensor detects whether the clutch pedal is pressed in a manual transmission vehicle, or bike. This is commonly used so the engine can only be started with the clutch pedal pressed (a safety interlock preventing the vehicle from lurching forward), and it can also briefly cut fuel or ignition during very fast gear changes in performance-oriented vehicles to make shifts smoother. On motorcycles, a similar sensor is used to allow neutral-safe starting.

What is a Gear Position Sensor?

The Gear Position Sensor tells the vehicle's computer which gear is currently engaged, whether in an automatic transmission (Park, Reverse, Neutral, Drive) or a manual gearbox or motorcycle transmission. This information is used to show the correct gear indicator on the dashboard, prevent starting the engine in gear, enable reverse lights only in Reverse, and let the ECU adjust engine mapping appropriately for the selected gear.

What is a Tire Pressure Monitoring Sensor (TPMS)?

A Tire Pressure Monitoring Sensor is fitted inside each wheel, usually attached to the valve stem, and it continuously measures the air pressure (and often temperature) inside that tire, transmitting the reading wirelessly to a receiver in the vehicle. If pressure in any tire drops below a safe level, a warning light appears on the dashboard, alerting the driver before a slow leak becomes a dangerous blowout or causes uneven tyre wear and higher fuel consumption.

What is a Parking Ultrasonic Distance Sensor?

Parking sensors, usually mounted in the front and rear bumpers, send out ultrasonic sound waves and measure how long the echo takes to bounce back off a nearby object, such as a wall or another vehicle. As the vehicle gets closer to the obstacle, the beeping warning sound speeds up, and many vehicles also show the estimated distance visually on the dashboard or infotainment screen. This helps drivers park safely and avoid low-speed collisions in tight spaces.

What is a Rain Sensor?

A Rain Sensor is usually mounted behind the windshield near the rear-view mirror and uses an infrared light beam to detect water droplets on the glass. When rain is detected, it automatically switches on the wipers and adjusts their speed to match how heavily it is raining, without the driver needing to operate them manually. This is a common comfort and convenience feature in mid-range and premium petrol cars.

What is an Ambient Light Sensor?

The Ambient Light Sensor, usually placed on top of the dashboard or near the windshield, continuously measures the level of natural light outside the vehicle. When it senses that daylight has fallen below a set threshold, such as at dusk or when entering a tunnel, it automatically switches on the headlights without the driver having to do so manually. It is also often used to automatically adjust the brightness of the dashboard display for comfortable viewing.

What is a Bank Angle (Tip-Over) Sensor on a motorcycle?

The Bank Angle Sensor, fitted mainly on petrol motorcycles and scooters, continuously measures the lean angle of the bike. If the bike leans beyond a safe angle and falls over — for example, in an accident or a stationary tip-over — the sensor instantly signals the ECU to cut off the fuel pump, ignition, and sometimes the engine itself. This important safety feature helps reduce the risk of fire or the engine continuing to run dangerously while the bike is lying down.

What is a Battery Voltage / Charging Sensor?

The Battery Voltage Sensor, often called an Intelligent Battery Sensor, is fitted directly on the battery terminal and continuously monitors the battery's voltage, current, and temperature. This data helps the ECU decide exactly how much charging current the alternator should supply, improving fuel efficiency by not over-charging the battery unnecessarily, especially in vehicles with start-stop systems. It also helps warn the driver early if the battery is weakening and unlikely to start the vehicle reliably.