How to fix common car problems yourself

Before you start: stay safe

Knowing how to fix a car problem yourself can save a tow, a call-out fee or a wasted trip to the workshop. It only pays off if you do it safely.

• Park on firm, level ground, put the handbrake on and switch the engine off.
• Let a hot engine cool before touching anything under the bonnet.
• Never work under a car held up only by a jack. Use proper axle stands or ramps.
• Disconnect the battery before working on wiring, and protect your eyes and hands around the battery.

Warning lights use a simple colour code. Red means stop or get help soon, amber means have it checked, and green or blue lights are just information.

Warning lights: ABS and ESP

ABS light

When the ABS light comes on, the anti-lock braking system has switched itself off because of a fault. The ordinary brakes still work. Common causes are a dirty or damaged wheel speed sensor, a broken sensor wire near a wheel, low brake fluid or, less often, a faulty ABS module.

To fix the ABS light on a car, start with the simple checks:

1. Check the brake fluid level in the reservoir under the bonnet.
2. Check the fuses for the ABS system, using the diagram in the handbook.
3. Look at the sensor wiring behind each wheel for damage, especially after a pothole, kerb strike or tyre change.
4. Read the fault code. An OBD scanner that supports ABS codes shows which sensor or circuit has the problem. Basic engine-only readers can’t see ABS faults.

Clearing the code without fixing the cause only makes the light come back.

ESP or stability control light

A flashing ESP light while you are cornering or on a slippery road is normal: it means the system is working. If the light stays on, the system has a fault or has been switched off. Check you haven’t pressed the ESP off button. The stability system uses the same wheel speed sensors as the ABS, so the two lights often come on together. On some cars the steering angle sensor needs recalibrating after a wheel alignment or battery change, which a workshop can do with a scan tool.

Overheating: what to do and temporary fixes

If the temperature gauge climbs or a red coolant light comes on, act straight away.

1. Turn off the air con and turn the heater to full hot with the fan on high. It is uncomfortable, but it pulls heat away from the engine as a temporary fix for an overheating car while you find a safe place to stop.
2. Pull over and switch off the engine.
3. Wait at least 30 minutes. Never open the radiator or coolant cap on a hot engine: the coolant is under pressure and can scald.
4. Check the coolant level in the reservoir once it is cool, and look for leaks, a split hose or a wet patch under the car.
5. Top up if it is low. Use coolant if you have it. Plain water will do in an emergency, but get the mixture corrected afterwards.

If the coolant was full, the cause may be a cooling fan that isn’t switching on, a failed water pump or a thermostat stuck closed. Replacing a car thermostat is a manageable job on some engines and a long one on others. Either way, the cooling system needs bleeding of air afterwards, so many owners leave it to a mechanic. If the car overheats again, have it towed rather than driving it.

Oil leaks

Engine oil is brown or black and feels slippery. To find a leak, put a piece of cardboard under the engine overnight to see where the drips land, then look above that spot. Cleaning the engine first makes the fresh oil easier to see.

• Check the oil filler cap is on properly and its seal is intact.
• Check the sump plug and oil filter, especially if the leak started after an oil change.
• Oil on top of the engine and around the spark plugs often comes from the rocker cover gasket.

Stop-leak additives can swell old seals and slow a leak for a while, but they are not a repair. Keep the oil topped up in the meantime, and get it fixed soon if oil is dripping onto the exhaust, because it can catch fire.

Corroded battery terminals

White, blue or green crust on the battery terminals stops current flowing and can make a good battery seem flat. To fix corroded car battery terminals:

1. Put on gloves and eye protection. The deposits contain acid.
2. Disconnect the negative (−) clamp first, then the positive (+).
3. Scrub the terminals and clamps with a solution of baking soda and water and an old toothbrush. It will fizz as it neutralises the acid.
4. Wipe clean and dry with a damp cloth, then a dry one.
5. Reconnect positive first, then negative, tighten the clamps and smear a little petroleum jelly or terminal grease on top.

If the battery case is swollen, cracked or leaking, replace the battery rather than cleaning it.

Windows, central locking and electrics

Window won’t go up

Check the window lock button on the driver’s door, then try both the driver’s master switch and the switch on the door itself. Listen as you press it. Silence points to a fuse, switch or motor. If you can hear the motor but the glass doesn’t move, or the glass drops into the door, the regulator has broken. To get home, you can sometimes help the glass up by hand while holding the switch. If the one-touch function stops working after a battery change, hold the switch in the up position for a few seconds after the window closes to reset it.

Sticky or slow windows

A window that moves slowly or judders usually has dirty, dry rubber channels. Clean the channels and apply a silicone spray made for rubber seals. A window that is slow even after that may have a tired motor.

Central locking

If the remote doesn’t work but the key does, replace the remote battery first. If one door won’t lock or unlock with the others, its door lock actuator is probably failing. If none of the doors respond, check the fuse before suspecting the control module. Fixing central locking in a car beyond these checks is a job for an auto electrician.

Small interior fixes

• Loose air vents. Vents are held in by plastic clips that break with age. Many vent units unclip from the dashboard and can be replaced as a part, so check before reaching for glue.
• Speakers not working. Check the stereo’s balance and fader settings first, then the fuse. If one speaker is silent, the connector behind the door trim may have come loose or the speaker may have blown.
• Bluetooth audio delay. Update your phone and the car’s software, delete the pairing on both and pair again, and turn off the phone’s battery saver. A cable connection through USB, Apple CarPlay or Android Auto gives the least lag.
• Car mats. Replace worn mats and make sure they are held by the retaining clips in the floor. A loose mat that slides under the pedals is dangerous.

If a fix isn’t working, or you’re not sure what you’re looking at, stop and get a professional opinion. It is usually cheaper than undoing a DIY repair.