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 switches
Resume switch
Cancel switch
Clock spring
Speed control warning indicator.

The speed control system also uses inputs from the brake pedal switch, the APP (accelerator pedal position) sensor, the ECM (engine control module) and the ABS (anti-lock brake system) module.

The speed control is operated by the driver using only the steering wheel switches. When speed control is active, the ECM regulates the PWM (pulse width modulation) signals to the fuel injectors to adjust the fuel supply as required to maintain the set speed.

During speed control operation, the ECM controls vehicle speed by adjusting fuel injection duration and timing. 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.
The difference between actual speed and the set speed is too great.
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.

There are 4 standard speed control switches:

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

The standard speed control switches are located on the RH (right-hand) side of the steering wheel. 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 LIN node which transmits the data to the CJB (central junction box) which passes the data onto the high speed CAN bus. In the event of the ECM logging a cruise switch fault DTC (diagnostic trouble code), fault finding should start at the switch assembly and clockspring. The ECM diagnostic detects that the switch assembly control module hasn't provided an updated live counter.