Keyless fobs

Regarding keyless entry and keyless start systems, is the keyfob signal that's used to unlock the door the same as the signal used to switch on the ignition and start the engine? Also, does the code/signal change each time the system is operated, as with the rolling code in an older version of the immobiliser with the transponder fitted inside the ignition key? Peter Kenny Althugh there are slight variations between different car manufacturers, the systems work by using a remote function module in the vehicle. The unit detects the passive signal being given off by the remote key-fob and, provided that signal is correct, allows the ignition to be activated and the steering lock to be released. On vehicles that are fitted with these systems, the steering lock needs to be activated by a solenoid.

The systems normally use a rolling or hopping code which will change at each detection or operation of the system. To prevent the vehicle and keyfob becoming out of sync too easily, there is normally a safety margin of around 250 different code changes before the systems will not talk to each other. Using a 40-bit rolling code, the permutations give a possibility of around one trillion different codes. This replaces the immobiliser system used on vehicles with a standard key, as the system itself is coded and it is this which provides the security.

The keyless entry system uses the same key with the signal being picked up by small antennae normally within the front door handles and the boot. Most keyless entry vehicles also have remote buttons on the fob, but these will operate on a different frequency to the passive system. The passive system uses an LF signal (25 khz) and the remote entry is 433.92 MHZ for European vehicles.