Garage speak – our guide to understanding car mechanic jargon

Garage speak – our guide to understanding car mechanic jargon
It can be daunting going to the garage for the average driver.

According to research to support the launch of the RAC’s complete breakdown policies more than half of drivers (56%) say they’ve been left struggling to understand the language used by garages when describing faults with cars.

As part of our complete breakdown service that includes garage support as standard, we've put together a jargon buster to help you better understand the lingo next time you take your car for a check-up.


abs warning light

Anti-lock braking systems (ABS) prevent your wheels from locking up so you can maintain grip on the road when you press hard on the brake pedal.

The technology comes as standard on modern cars and helps avoid dangerous skidding situations. If your ABS system is faulty, the dashboard warning light above should illuminate.


ADAS or Advanced Driver Assistance Systems come in many forms. Imagine systems that automatically brake when the car detects an imminent crash or helps with steering to maintain your position in a driving lane.

The systems are designed to help rather than replace drivers and it’s vital you keep control of a vehicle while using them. Car safety experts Thatcham Research and Euro NCAP launched a first-of-its-kind grading system in October 2020 to help drivers understand ADAS technology.



AGM or Absorbent Glass Mat batteries are well known for their performance in stop/start engines. They’re more reliable than conventional lead-acid batteries when starting an engine from cold and are well suited to vehicles with sophisticated electric systems.

Although stop/start technology can help reduce fuel consumption by 5%-10% not all cars are compatible with AGM batteries. You can check if your vehicle works with an AGM by entering your reg in the RAC battery checker.


Automated Lane Keeping Systems or ALKS are one of many ADAS or Advanced Driver Assistance Systems.

ALKS technology can steer vehicles for extended periods of time to help maintain your position in a driving lane.

In August 2020, the Department for Transport announced a consultation to consider how the technology could make driving “safer, smoother and easier for motorists”

Big end

The ‘big end’ on a car is easy to understand if you picture the pistons that work under your bonnet.

It simply refers to the larger side of a connecting rod or ‘conrod’ in a combustion engine. The rod powers the back and forth motion of the piston into the rotating motion of the crankshaft.

‘Rod knock’, or the sound of rods knocking against the crank, can be heard when bearings inside the engine have extra space and movement is affected. 

MOT due?

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MOT due?
MOT due?


Dampers or shocks minimise the up and down motion in a car when tyres hit bumps in the road. They are usually used alongside springs to form the suspension system for a smoother ride.

The dampers use hydraulic fluid to dissipate kinetic (moving) energy in the springs to heat energy.

Over time the shocks can become worn and less effective, meaning your car is more likely to bounce on an uneven surface.


dpf warning light

A DPF can be found in the exhaust system on diesel cars. The Diesel Particulate Filters (DPFs) are fitted on cars to collect soot and reduce emissions.

You may need to visit a garage if your DPF becomes clogged with soot and needs to ‘regenerate’. If you see the warning light above appear on your dashboard, you can contact an RAC Approved Garage for a ‘forced regeneration’.


An electrohydraulic brake system (EHB) uses an electric motor controlled by sensors to apply hydraulic pressure on brakes.

The system often appears in hybrid and electric cars and is sometimes referred to as sensotronic brake control (SBC), offering improved brake power and shorter braking distances.

Its smart sensors allow stopping power to vary between wheels for a safer drop in speed.

EML light

eml dashboard warning light

An EML or engine management light will illuminate on your dashboard if there’s a problem with your engine module. The light is connected to the engine control unit and sometimes referred to as the ECU light.

You might notice a lack of power or stuttering as you press the accelerator, either way it’s important to find your nearest RAC approved garage as soon as possible. You can even get a mobile mechanic in to take a look from the convenience of your driveway.

Service, repair or MOT?

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Service, repair or MOT?
Service, repair or MOT?

Excess play

Mechanics may use the term excess play to describe a steering wheel that turns without properly moving tyres. Think of it as extra ‘give’ in your steering.

A loose steering wheel can have major problems when controlling your car, especially at high speeds. The excess play might occur in a number of parts in the steering system and it’s best to get professional help as soon as possible.

Head gasket

The head gasket sits between cylinders at the top of the engine and the engine block, the main structure of your engine.

It’s vital that the head gasket remains tightly sealed so that oil and coolant doesn’t leak into parts that they’re not designed to reach.

If you’re having trouble with milky oil, white exhaust smoke or an overheating engine you should check our head gasket guide to help diagnose the problem and enlist the help of an RAC expert from one of our motoring services.

MIL light

The malfunction indicator lamp or MIL is another name for the EML light. It will light up when there’s a problem with the fuel management system or the ‘electric brain’ of your engine.



You might hear a professional describe your car as misfiring. This simply means that cylinders in your engine are failing to work correctly.

When the ratio of fuel and oxygen isn’t what it should be your vehicle can lose power, give off more CO2 and run less efficiently.

If your car jerks while driving, the cylinders or other parts of the fuel-delivery system may be faulty and you should seek the help of a professional.

Car playing up?

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Car playing up?
Car playing up?


Your car’s module could be referred to as an electronic control module, ECM, or electronic control unit. The electric part uses sensors to perform calculations and work out timings in the fuel-ignition process.

The EML light should illuminate if there are problems with your module. If not, you may notice your engine misfiring or struggling to start up.

Poor fuel economy and reduced power are also tell-tale signs your module could be faulty.


A TPMS or tyre-pressure monitoring system does exactly what it says on the tin. The tools measure tyre pressure and give a reading in bar (metric) or pounds per square inch or PSI (imperial).

Your car’s bodywork or owner’s manual will tell you the ideal pressure for your vehicle which you should aim to check roughly once a month. Keeping your tyres properly inflated will help with fuel economy and improve the handling of your vehicle.


It may sound like a smart navigation tool but tracking refers to the angle and direction that your tyres are set to, or your wheel alignment.

As tyres hit kerbs or speed through potholes, they can turn away from a straight position. When this happens you might notice a dragging to one side when steering, uneven tyre wear or in extreme cases, vibration through the steering wheel.

If you need help fixing the problem, ask an RAC approved garage about wheel alignment services.

You can keep on track with your car's maintenance and save money by getting a service or MOT plan to spread the cost over two years.

Book a car service today

It’s easy to book a service online at one of our local approved garages. Find a trusted local garage with the RAC stamp of approval.

Book a car service today
Book a car service today