Ignition switch (ISM), detailed description
Ignition switch (ISM), detailed description |
As soon as the key is inserted the ISM will continuously send key position on the communication cable to the CIM. The CIM then conveys key position to the P and I-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 the ISM. +15 receives battery voltage only in positions ON and ST. There are also three relays that are activated directly by the cable from +15, one in each fuse box. All the control modules on the I-bus depend on the key position transmitted by the CIM and are not wired for +15 (except the airbag control module).
Besides separate leads for B and +15, there is also one for +X, which is energised 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.