Top Ten Breakdown Causes
The most common problems dealt with by AA patrols
These are the most common problems dealt with by AA patrols. Many can be fixed at the roadside, but most can be avoided with the correct preventative care.
Flat or faulty battery
Most common problems are caused by terminals and clamp connections or by a loss of voltage, often caused by constant use on short journeys without regular recharging.
At every service, check that terminals have been cleaned and protected from corrosion with a layer of petroleum jelly or grease. Clamps and connections must be secure.
If you seldom make a long journey, a fortnightly overnight charge prolongs battery life.
Modern maintenance-free batteries need no top-up.
Read about battery problems in winter »
Lost keys
Many modern cars have a 'transponder' key to prevent theft.
If you lose the key, recovery to an authorised dealer is usually the only answer.
Even a dealer may take several days to obtain a replacement, so always carry a spare set of keys.
Flat/damaged tyres and wheels
Know the correct pressures for different speeds and loads, and adjust accordingly.
Kerb impact can damage sidewalls and, possibly wheel rims. Both can result in slow leaks. Consult a specialist tyre dealer if any damage is visible.
When checking tread depth, look for uneven tyre wear – the wheels may be misaligned.
Look at the spare tyre. A worn or flat spare won't be of use in an emergency.
Check that the jack and wheel-removal tools are in good condition and that the key or removal tool for locking wheel nuts is accessible.
Alternator faults
Persistent battery problems and dim headlights when the engine is idling can indicate alternator/generator faults.
Belts driving the alternator may also operate the radiator fan and water pump. A red ignition warning light plus a rapid rise in engine temperature could indicate a broken belt. Stop immediately.
Starter motor
Though usually robust, starter motors can fail.
Good, regular garage maintenance should highlight potential faults.
Distributor cap
Moisture and dirt are the chief enemies of this vital ignition-system component.
A crack in the cap's insulation may be almost invisible but can be sufficient to allow high ignition voltage to leak away, especially in damp weather, so there may be no ignition spark.
Replace the cap at the car manufacturer's recommended intervals.
If the weather protection covering the cap splits, replace it.
Fuel problems
Empty fuel tanks cost AA patrols a lot of time and members unnecessary inconvenience.
Fill up at the start of your journey.
Every year more than 100,000 motorists put the wrong fuel in their car – petrol in diesel engines or vice versa. In these cases the car will have to be recovered to a garage and draining the tank and disposing of contaminated fuel is expensive.
Clutch cables
The clutch cable is under high stress. Abrasion can weaken the wire strands until they break.
Temporary repairs can often be made at the roadside, but replacement at the first signs of wear is the best answer.
Spark plugs
The spark plug is a much-neglected part of the ignition system.
Make sure that you replace plugs at the manufacturer's recommended service intervals.
HT leads
High-tension (HT) leads and their connections can deteriorate with age. Water and dirt enter cracks in the insulation, reducing the ignition voltage.
Damp-repellent sprays are only a temporary solution.
Ask your garage to check the condition of the leads and replace as necessary.
http://www.theaa.com/motoring_advice/breakdown_advice/top_ten_causes.html
You won't lose all your warranty if you don't get it serviced as per the schedule, just the bits relating to items affected by the items which should be serviced 
