Otto Explains — Car Terms
Automotive Terminology Explained: A Driver’s Glossary
Short Answer
This glossary explains the car terms Otto uses most, in plain language: from the engine control unit (ECU) and fault codes to ABS, oil viscosity grades and the alternator. Each entry gives a short definition and points to the Otto article that covers the subject in depth. The same approved terms are used in English and Arabic across every Otto article.
What do the diagnostic and warning-light terms mean?
The engine control unit (ECU) is the computer that manages the engine's fuel mixture, ignition timing and emissions system; it also monitors how the car runs and helps diagnose problems. The check engine light is the dashboard lamp the car's on-board diagnostic system switches on when it detects a fault in an emissions-related component; when it flashes, it signals a more serious malfunction that could damage the catalytic converter. Otto explains what the check engine light means and what to do. A fault code is the information the system stores about a detected fault so a technician can trace it. A diagnostic scan reads those codes and live data, the sensor readings shown in real time, but a scan is not a full diagnosis: see what a diagnostic scan can tell you.
What do the engine and cooling terms mean?
Spark plugs ignite the air-fuel mixture using energy from the ignition coil. A misfire happens when the spark fails to jump the plug's gap properly, for example because of fouling or worn ignition parts. A turbocharger uses energy from the exhaust gases to spin a turbine linked to a compressor, which pushes more air into the engine so more fuel can be burned. The catalytic converter in the exhaust treats hydrocarbons, carbon monoxide and oxides of nitrogen from petrol engines. In the cooling system, the water pump circulates coolant between the engine and the radiator, the thermostat is a valve that controls when coolant flows to the radiator, and airflow from driving and the cooling fan lets the radiator shed heat. When the temperature gauge climbs, Otto explains what to do if your car is overheating.
What do the oil and maintenance terms mean?
An oil's viscosity grade, such as 5W-30, describes how it flows: the W stands for winter, the first number relates to flow when the oil is cold, such as at start-up, and the second to flow at normal operating temperature. Manufacturers specify which grades are approved for their engines. A service interval is the time or distance between scheduled services. Otto never gives one figure for every car: your manufacturer's schedule applies, including its severe-service schedule where conditions such as heat, dust, short trips, long idling and stop-start traffic call for it. Otto explains how often engine oil should be changed.
What do the brake and safety-system terms mean?
In a disc brake, brake fluid pressure moves pistons in the caliper, which press the brake pads against both sides of the brake disc; the friction slows the wheel and the disc absorbs the heat. Otto explains when brake pads need replacing. ABS, the anti-lock braking system, stops the wheels locking under hard braking by reducing and restoring brake pressure up to 40 times a second, so you can still steer. Electronic stability control (ESC) helps prevent skids by braking individual wheels automatically, and automatic emergency braking (AEB) brakes on its own if it detects something in the car's path. Airbags (SRS) inflate instantly in a crash and work best when seat belts are worn, and a seat-belt pretensioner tightens the belt at the start of a crash. If the airbag warning light stays on, read what the airbag light means.
What do the gearbox and suspension terms mean?
The gearbox, or transmission, transfers power from the engine to the wheels. Shock absorbers control the bouncing and rebound movement of the springs and suspension and help keep the tyres in contact with the road. Despite a common belief, they don't carry the car's weight.
What do the electrical and air-conditioning terms mean?
The battery supplies the current to start the car. The starter motor is the electric motor that turns the engine over, and the alternator, driven by a belt, generates electricity to keep the battery charged. When a car won't start, Otto explains the most common reasons. In the air-conditioning system, the refrigerant absorbs heat from the cabin, and the condenser at the front of the car releases that heat to the outside air. For weak cooling, see why a car's AC stops cooling.
Common Questions
- What does the W in 5W-30 stand for? Winter. The number before the W relates to how the oil flows when cold, such as at start-up, and the number after it to how it flows at normal operating temperature. Use the grade your manufacturer approves.
- What is the difference between ABS and ESC? ABS stops the wheels locking when you brake hard, so you can still steer. ESC helps prevent the car from skidding by automatically braking individual wheels.
- Do shock absorbers hold the car up? No. Shock absorbers control the movement of the springs and help keep the tyres on the road; they don't support the car's weight.
- Is a diagnostic scan the same as a diagnosis? No. A scan reads the fault codes and live data the car has stored, which point a technician in a direction. Testing is still needed to confirm the cause before anything is replaced.