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Ignition switch, detailed description

Ignition switch, detailed description


Inserting the key closes a contact, whereby +B is energized. The column integration module (CIM) is woken up via a direct lead for +B from the ignition switch (ISM). ISM releases the steering column lock (SCL) locking pin after a command from CIM. ISM wakes up, reads the key transponder code and sends the code on the communication cable to CIM. A code exchange then takes place to ensure that SCL and CIM belong together. If this code exchange and the key transponder code are approved, CIM will unlock SCL and CIM will send a signal to ISM via the communication cable to release the key so that it can be turned past LOCK to OFF and then to ON and ST. The key is blocked mechanically so that it can only be removed in LOCK position.

As soon as the key is inserted, ISM will transmit the key position continuously to CIM on the communication cable. CIM then conveys the key position to the P and I-buses. The infotainment control panel (ICM) also makes it available on the O-bus.

CIM also generates +54 as a bus signal. This is active in key position ON but not ST and is used by the body control module (BCM) to operate a relay in the instrument panel fuse signal.

The P-bus control modules are wired for +15 directly from ISM. +15 receives battery voltage only in positions ON and ST. There are also three relays that are activated directly by the lead from +15, one in each fuse box. All the control modules on the O-bus and I-bus depend on the key position transmitted by CIM and are not wired for +15 (except the airbag control module on the I-bus).

Besides separate leads for B and +15, there is also one for +X, which is energized in positions ON and OFF. +X is connected to the engine control module (ECM) for activating the fuel pump so that it can build up pressure at an early stage.