Land Rover Discovery Owners & Service Manuals

Land Rover Discovery: Vehicle Dynamic Suspension - Operation

The SUM uses a combination of information from other system modules and data from the height sensors to measure the vehicle and suspension states and driver inputs. Using this information, the SUM applies algorithms to control the shock absorbers for the current driving conditions.

The SUM receives the following signals on the high speed CAN Chassis bus from the stated system components:

  • Brake pressure - Anti-lock Brake System (ABS) control module.
  • Brake pressure quality factor - ABS control module.
  • Car configuration parameters - Central Junction Box (CJB).
  • Engine speed - Engine Control Module (ECM).
  • Engine speed quality factor - ECM.
  • Engine torque flywheel actual - ECM.
  • Engine torque flywheel actual quality factor - ECM.
  • Gear position target - Transmission Control Module (TCM) - automatic transmission vehicles only.
  • Lateral acceleration - ABS control module.
  • Power mode (ignition signal) - CJB.
  • Power mode quality factor - CJB.
  • Roll stability control mode - ABS control module.
  • Steering wheel angle - ABS control module.
  • Steering wheel angle speed - ABS control module.
  • Steering wheel angle status - ABS control module.
  • Terrain mode requested - Terrain Response (TR) switchpack - automatic transmission vehicles only.
  • Torque converter slip - TCM - automatic transmission vehicles only.
  • Vehicle information parameters HS - CJB.
  • Vehicle speed - ABS control module.
  • Vehicle speed quality factor - ABS control module.
  • Front left wheel speed - ABS control module.
  • Front left wheel speed quality factor - ABS control module.
  • Front right wheel speed - ABS control module.
  • Front right wheel speed quality factor - ABS control module.
  • Rear left wheel speed - ABS control module.
  • Rear left wheel speed quality factor - ABS control module.
  • Rear right wheel speed - ABS control module.
  • Rear right wheel speed quality factor - ABS control module.

The SUM also outputs information on the high speed CAN Chassis bus for use by other systems as follows:

  • Fault message - Instrument Cluster (IC).
  • Terrain mode change status - TR switchpack - automatic transmission vehicles only.
  • Terrain mode - TR switchpack - automatic transmission vehicles only.

The SUM monitors the input signals and operates the shock absorber solenoids. The input signals are used in control functions and a force required for each shock absorber, for each function, is calculated. An arbitrator monitors the force requirements from each function and apportions a force to a shock absorber. The force is converted to the appropriate current and sent to the shock absorber.

The control functions are as follows:

  • Body Control - Uses suspension height sensors and CAN bus inputs.

    Calculates road induced body motions 200 times a second and sets each shock absorber to the appropriate level to maintain a flat and level body attitude. Provides improved body control without loss of ride quality.

    Roll Rate Control - Uses CAN inputs. Predicts vehicle roll rate due to driver steering inputs 100 times a second and increases damping to reduce roll rate. Provides improved control and driver confidence.

  • Pitch Rate Control - Uses CAN inputs. Predicts vehicle pitch rate due to driver throttle and braking inputs 100 times a second and increases damping to reduce pitch rate. Provides improved control and driver confidence.
  • Bump Rebound Control - Uses suspension height sensor and CAN inputs.

    Monitors the position of the wheel 1000 times a second and increases the damping rate as the shock absorber approaches the end of its travel.

    Provides improved ride quality.

  • Wheel Control - Uses suspension height sensor and CAN inputs. Monitors the position of the wheel 1000 times a second and provides the appropriate level of damping for the suspension velocity.
  • Dynamic program - Uses suspension height sensor and CAN inputs. The Dynamic program uses a completely separate tune from the normal control, an alternative set-up for the body, wheel, roll rate, pitch rate and bump/rebound control to give a tighter, sportier driving feel.
  • Off-road modification - Uses suspension height sensors and CAN inputs.

    Evaluates the road surface roughness and appropriately adapts the level of damping control demanded from the various functions: body, wheel, roll rate, pitch rate and bump/rebound control.

Under normal road conditions, when the vehicle is stationary with the engine running, the dampers are set to the lowest damping condition to reduce power consumption.

The SUM has a constant power supply, and an ignition power feed from the Rear Junction Box (RJB). The ignition power feed relay is energized by the CJB. The relay remains energized for a period of time after the ignition is off. This allows the SUM to record and store any Diagnostic Trouble Code (DTC) relating to adaptive damping system faults.

CONTROL DIAGRAM

NOTE: A = Hardwired; AL = Pulse Width Modulation (PWM); AM = High speed - Controller Area Network (CAN) Chassis bus; AN = High speed CAN Powertrain bus.

CONTROL DIAGRAM

  1. Suspension Control Module (SUM)
  2. Engine Control Module (ECM)
  3. Instrument Cluster (IC)
  4. Transmission Control module (TCM)
  5. Transmission Control Switch (TCS)
  6. Central Junction Box (CJB)
  7. Rear Differential Control Module (RDCM)
  8. Anti-lock Brake System (ABS) control module
  9. Power Steering Control Module (PSCM)
  10. Terrain Response (TR) switchpack
  11. Gateway Module (GWM)
  12. Adaptive shock absorber (4 off)
  13. Ground wire
  14. Power supply
  15. Height sensor (4 off)

Vehicle dynamic suspension diagnosis and testing

PRINCIPLES OF OPERATION

For a detailed description of the Vehicle Dynamic Suspension, refer to the relevant Description and Operation section in the workshop manual. REFER to: Vehicle Dynamic Suspension (204-05 Vehicle Dynamic Suspension, Description and Operation).

INSPECTION AND VERIFICATION

CAUTION:

Diagnosis by substitution from a donor vehicle is NOT acceptable.

Substitution of control modules does not guarantee confirmation of a fault, and may also cause additional faults in the vehicle being tested and/or the donor vehicle.

NOTES:

  • If a control module or a component is suspect and the vehicle remains under manufacturer warranty, refer to the Warranty Policy and Procedures manual, or determine if any prior approval programme is in operation, prior to the installation of a new module/component.
  • When performing voltage or resistance tests, always use a digital multimeter that has the resolution ability to view 3 decimal places.

    For example, on the 2 volts range can measure 1mV or 2 K Ohm range can measure 1 Ohm. When testing resistance always take the resistance of the digital multimeter leads into account.

  • Check and rectify basic faults before beginning diagnostic routines involving pinpoint tests.
  1. Verify the customer concern
  2. Visually inspect for obvious signs of damage and system integrity

Visual Inspection

Visual Inspection

  1. If an obvious cause for an observed or reported concern is found, correct the cause (if possible) before proceeding to the next step
  2. If the cause is not visually evident, verify the symptom and refer to the Symptom Chart, alternatively check for Diagnostic Trouble Codes (DTCs) and refer to the DTC Index
  3. Check DDW for open campaigns. Refer to the corresponding bulletins and SSMs which may be valid for the specific customer complaint and carry out the recommendations as required

DTC INDEX

For a list of Diagnostic Trouble Codes (DTCs) that could be logged on this vehicle, please refer to Section 100-00. REFER to: Diagnostic Trouble Code Index - DTC: Suspension Control Module (SUM) (100-00 General Information, Description and Operation).

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