Speed Control: Notes

WARNING: This page is about a different car, the 2015 Jaguar XF, 2014 Jaguar XF, and 2013 Jaguar XF. However, it is still accessible from the selected car via links, so may be relevant.

The speed control system is integrated with the engine management system and uses fueling intervention to automatically maintain a set vehicle speed. Once engaged, the system can also be used to accelerate the vehicle without using the accelerator pedal. The speed control system comprises the following components:

'+' and '-' (set/accelerate and decelerate) steering wheel switchpack switches
Resume switch
Cancel switch
Clockspring
Speed control warning indicator.

The speed control system also uses inputs from the stop lamp switch, the APP sensor, the ECM and the ABS control module.

During speed control operation, when the accelerator pedal is pressed with speed control active, the ECM outputs a calculated throttle angle signal in place of the actual throttle angle signals produced by the APP sensor. The calculated throttle angle is derived from fuel demand based on the torque required to overcome the rolling resistance (vehicle motion drag).

The minimum set speed for speed control is 20 mph (32 (km/h). Speed control is automatically suspended if the following conditions apply:

Vehicle speed falls below 20 mph (32 km/h)
The brake pedal is pressed
The 'Cancel' button is pressed
Neutral, Park or Reverse gear is selected
Automatic Speed Limiter (ASL) is active
Electric park brake is operated
If the accelerator pedal is used to accelerate beyond the set speed for too long (more than 5 minutes)
Stability control system intervention
System error causes shut-off. These system errors can include:
- the adaptive speed control module
- the ABS control module
- speed control switch failure
- clockspring failure
- CAN or LIN bus errors
- stop lamp switch failure
- 'PARK' or 'NEUTRAL' detection error
- vehicle speed error
- vehicle speed control system errors
- electric throttle or APP sensor errors
- electric park brake errors.

There are four standard speed control switches:

Set speed '+' accelerate switch
Decelerate '-' switch
Cancel switch
Resume switch.

The standard speed control switches are located on the right steering wheel switchpack. The switches are resistive ladder type switches which vary the resistance of a voltage signal sent to them. The resistive ladder is wired to a control module within the switch assembly, the control module is a Local Interconnect Network (LIN) node which transmits the data to the Central Junction Box (CJB) which passes the data onto the high speed Controller Area Network (CAN) bus. In the event of the ECM logging a cruise switch fault Diagnostic Trouble Code (DTC), fault finding should start at the steering wheel switchpack assembly and clockspring. The ECM diagnostic detects various failure types such as switchpack assembly hasn't provided an updated live counter, an incorrect checksum for the data received and switch stuck on detection.