Ignition Switch

Ignition Switch

the ignition switch signal enables the ECM to detect if the ignition is on or off. the signal is a power feed that is connected to the ECM while the ignition switch is positions II and III. On the New Range Rover, the power feed comes from the ignition relay in the engine compartment fuse box.

When it first receives the signal, the ECM 'wakes-up' and initiates a power-up sequence to enable engine starting and operation. the power-up sequence includes energizing the main relay, which supplies the main power feed to the ECM, energizing the fuel pump relay and initiating a self check of the engine management system.

When it detects the ignition has been turned off the ECM stops activating the fuel injectors and ignition coil to stop the engine, and de-energizes the fuel pump relay, but keeps the main relay energized while it performs a power down sequence. During the power down sequence the ECM records the engine sensor values required for a quick-start function to operate the next time the engine is cranked. At the end of the power down sequence, the ECM de-energizes the main relay to switch itself off.