System Operation

WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2015 Jaguar XF, 2014 Jaguar XF, 2013 Jaguar XF, 2012 Jaguar XF, and 2011 Jaguar XF. However, it is still accessible from the selected car via links, so may be relevant.

The passive start function prevents the vehicle from being started by unauthorized persons. It does this by immobilizing the ignition, fuel and engine crank functions. The system is automatic and requires no input from the driver.

At the request of the Central Junction Box (CJB), the keyless vehicle module prompts each of the Low Frequency (LF) antennae to output a signal. When the Smart Key is in the vehicle cabin, it detects the LF signals and responds with a Radio Frequency (RF) data-identification signal back to the keyless vehicle module via the RF receiver.

If the data received matches that stored in the keyless vehicle module it continues the passive start process by communicating a 'Smart Key valid' signal to the CJB via the medium speed CAN (controller area network) bus.

Once the CJB receives the authorization and confirms a response with an internal calculation, it passes the result to the instrument cluster on the medium speed CAN bus.

Before the instrument cluster sends a mobilization signal to the Engine Control Module (ECM) it will exchange encrypted data with:

The electric steering lock mechanism to authorize unlocking the steering column.
The Rear Junction Box (RJB) to authorize fuel pump operation. Once the RJB receives the authorization and confirms the response with an internal calculation, it will enable the FPDM (fuel pump driver module).
The CJB to authorize the ignition status. If the drive selector is in the park position and the driver presses the brake pedal and simultaneously presses the start/stop switch, the CJB interprets this as an engine crank request. Before the engine crank request is allowed, the CJB compares a brake pressure signal received from the ABS (anti-lock brake system) module. The brake pressure signal is compared to an internally stored threshold value within the CJB. If the signal is greater than the stored threshold value, a crank request signal is sent to the ECM on the high speed CAN bus.

Once these factors have been confirmed, and the vehicle is in 'Park', the engine can be started by pressing the brake pedal and the Stop/Start button simultaneously.

To ensure optimum long term reliability of the smart key the battery must be replaced with a brand new, unused battery. If a used battery is installed the "SMART KEY BATTERY LOW" message may not be cleared. To avoid contamination of the contacts the battery should be removed from its packaging and installed into the smart key while wearing gloves. To confirm that the replacement battery is working correctly press the unlock button twice while holding the smart key outside the vehicle, then enter the vehicle with the smart key, press the start button and confirm that the "SMART KEY BATTERY LOW" message is not displayed.