Power Supplies: Description

The ECM requires a permanent battery level voltage supply and a switched battery level voltage supply. The switched voltage supply is controlled by the ECM via a relay based on the condition of the ignition switch input (key position 2). At "key off" the ECM will maintain the switched supply active until various internal self-checks have been completed. See Fig 1 .

There are three battery voltage plausibility checks during which a fault is detected if:

1. The battery voltage supply is less than a minimum voltage threshold.
2. The battery voltage supply is greater than a maximum voltage threshold and a jump-start condition has not been detected.
3. The battery voltage supply is less than a voltage threshold 60 seconds after the engine has been started.

Fig 1: Power Supplies Battery Voltage DTC Testing

Courtesy of LAND ROVER NORTH AMERICA, INC.