Check the handbook - many warning lights are specific to the manufacturer or even the model
As cars have become more complex, the number of different dashboad warning lights has grown significantly. Modern electronic systems like airbags or stability control are constantly self-testing and it's important for you to know whether a warning light requires immediate attention or whether you can continue your journey and get a garage to investigate later.
If a warning light comes on (or fails to extinguish after you've started the engine) you should stop as soon as possible in a safe place.
Many warning lights are specific to the car make or even the model - the vehicle handbook should give you a detailed explanation of their meaning and the action to take.
MOT
Some new mandatory test items are included in the MOT test from January 2012. These will include checks for the correct function of the following warning lights, where fitted:
Oil
This light should illuminate when the ignition is switched on and should extinguish as soon as the engine starts.
If the light stays on after starting or illuminates during a journey, stop immediately, switch off the engine and check the engine oil level.
Top up straight away if the level is low.
If the warning lamp illuminates, even though the oil level is correct, do not start the engine and seek assistance.
Charging
This light should illuminate when the ignition is switched on and should extinguish as soon as the engine starts.
If it does not illuminate at all, or if it illuminates while driving, your battery is not being charged as there is a fault with your charging system.
This may be due to one of the following;
If the drive belt is broken, it must be replaced before you restart the engine. The coolant system may rely on this belt and its failure could cause the engine to overheat, in turn causing engine damage.
Immediately move the vehicle to a safe location and switch off the engine. Do not restart the engine and seek assistance.
Brakes
This light will remain illuminated when the handbrake is engaged. Illumination after releasing the handbrake may indicate low brake fluid level.
Refer the the handbook and add the correct brake fluid at once to bring the level up to the MAX mark. As the brakes wear the fluid level will slowly drop. Check your brake fluid level frequently to ensure there is no further rapid loss of fluid.
If the brake fluid is too low and brake pedal travel is distinctly longer than usual, one of the two hydraulic brake circuits may have failed. Do not continue your journey and seek assistance.
If the light remains illuminated, even though the brake fluid level is correct, this may indicate a sensor fault. Take your vehicle to a dealer or garage as soon as possible.
DPF
Diesel Particulate filters (DPF) or 'traps' do just that, they catch bits of soot in the exhaust.
As with any filter (think of the bag in your vacuum cleaner) they have to be emptied regularly to maintain performance. For a DPF this process is called 'regeneration' – the accumulated soot is burnt off at high temperature to leave only a tiny ash residue. Regeneration may be either passive or active.
Passive regeneration takes place automatically on motorway-type runs when the exhaust temperature is high. Many cars don't get this sort of use though so manufacturers have to design-in 'active' regeneration where the engine management computer (ECU) takes control of the process.
When the soot loading in the filter reaches a set limit (about 45%) the ECU can make small adjustments to the fuel injection timing to increase the exhaust temperature and initiate regeneration. If the journey's a bit stop/start the regeneration may not complete and the warning light will illuminate to show that the DPF is partially blocked.
It should be possible to start a complete regeneration and clear the warning light by driving for 10 minutes or so at speeds greater than 40mph.
Engine management
Illuminates when the ignition is switched on. It should extinguish as soon as the engine starts.
If it illuminates with the engine running, it indicates a malfunction with the engine management system. Have this checked as soon as possible.
If it flashes when driving, reduce the vehicle speed immediately until the light illuminates constantly. If it continues to flash, avoid heavy acceleration and high engine speed, stop the vehicle and have it checked immediately.
On some vehicles this light may be red – again stop the vehicle and seek assistance.
If it is safe to do so, try stopping the vehicle, switching off the engine, wait two minutes, then restarting the engine to reset the engine management system.
With the light illuminated, the vehicle is still safe to drive as long as no other faults are apparent with the engine. Have the vehicle checked by a dealer or garage as soon as possible to avoid any damage being caused to the catalytic converter.
ABS
When the ignition is switched on, the light illuminates briefly to confirm that the system is operational.
If it illuminates when driving, it indicates a malfunction. Have this checked as soon as possible.
Normal braking (without ABS) will be generally be maintained and many cars will be safe to drive on, but some will not - check the handbook for advice.
Have the vehicle checked by a dealer or garage as soon as possible.
Brakes & ABS
If both warning lights illuminate at the same time when driving, stop the vehicle as soon as it is safe to do so.
Reduce vehicle speed gradually and immediately move the vehicle to a safe location. Use the brakes with great care. Do not step on the brake pedal abruptly. Seek assistance.
Fuel filter
This light illuminates when the ignition is switched on and should extinguish after a few seconds.
If it illuminates while driving, it indicates that water has been detected in the fuel filter.
This light warns you that the amount of accumulated water in the fuel filter has reached the specified level.
Normally the vehicle is quite safe to drive, but have the accumulated water in the fuel filter drained off as soon as possible.
If the vehicle has just been re-fuelled, immediately move the vehicle to a safe location and switch off the engine. The fuel may have been contaminated and could cause damage to the injection system.
(1 November 2011)
