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Car Keys

A guide to car keys and remote controls

Most modern car keys are three keys in one.

  1. A mechanical key will release the steering lock
  2. A coded 'electronic transponder chip' is read by the car when the key is inserted in the ignition
  3. A remote control will unlock the doors and turn off the alarm

These keys are secure but are also expensive and time consuming to replace if lost or broken. Treat keys as you would expensive jewellery – keep them in a safe/secure place.

keys Transponder keys
Master keys
Rolling codes
Remote controls
What if the remote doesn't work?

Transponder keys

  • Electronic, coded transponder chips embedded in the plastic body of the key were introduced from 1995. The chip is passive, so it doesn't need a battery – the code is read when you turn the key in the ignition.
  • If the transponder chip is broken or missing, the engine won't start.
  • You will need to return to the dealer if you wish to replace your key. The dealer will have to reprogramme the immobiliser's control unit to recognise the new key code.

Master keys

Many early cars were supplied with a 'master key' (often red), which was not intended for normal use. The dealer uses the master key to programme a new or replacement key for the car.

  • Unfortunately, if you damage or lose the master key it could cost hundreds of pounds to replace. You may have to replace the complete engine management system costing more than £1,000.
  • Car manufacturers have virtually stopped using master keys. They now hold car-specific security information in a central database, which the dealer uses when reprogramming the car and a replacement key.
  • If you're buying a used car, check the handbook. Make sure you get all the keys including a master key if necessary.

Rolling codes

Early transponders used 'fixed codes' – the key sends exactly the same coded signal every time it's used.

  • Keys with 'rolling codes', which means the transponder code changes every time the key is used, were introduced from 1999 and are now very common.
  • These should be virtually impossible to copy. They offer improved security but they're even more expensive to replace if lost.
  • Time and cost vary from manufacturer to manufacturer – expect to pay around £100 and wait up to three days for a replacement key.
  • The key might be even more expensive to replace if it includes a remote control for operating central locking and the alarm.

Remote controls

More that 90% of all new cars are now supplied with a remote control to unlock the doors and turn off the alarm. Very convenient, but not without their problems.

  • Some use infrared but most use a radio transmitter to send a coded signal to a receiver on the car.
  • The operating frequency (418Mhz or 433.92Mhz) is close to those used by MoD communication, radio amateurs and other common applications.
  • Interference can occur and in extreme cases the car can't be unlocked.
  • The AA helped to establish the Radio Activated Key Entry (RAKE) Committee in 1997 to ensure that the problem was recognised and researched. Car manufacturers were encouraged to improve the design of their systems to make them less susceptible to interference.
  • Modern cars are generally now much less likely to suffer from radio interference but the problem remains for older cars, particularly those built before 1995.

What if the remote control doesn't work?

  1. Check the battery is not flat.
  2. If you suspect radio interference try using the remote control close to your vehicle.
  3. In extreme cases, AA patrols have had to tow vehicles away from interference, so the remote can work.
  4. Cars with remote central locking should have a bypass system using the normal metal key to unlock the doors without setting the alarm off. This 'auxiliary entry' system should be explained in the handbook.
  5. Having said that, the handbook will probably be locked in the car when the remote fails – familiarise yourself with the procedure now.