Electronic Suspension Control

Electronic Suspension Control Description and Operation

Electronic Suspension Control Description

The electronic suspension control system system independently controls each of the 4 shock absorbers in order to control the vehicle ride characteristics. The electronic suspension control (ESC) system is capable of making these changes within milliseconds. The ESC system consists of the following major components:

* The electronic suspension (ESC) module

* The front/rear position sensors

* The front/rear adjustable shock absorbers

* The shock absorber electrical actuators, which are integrated within the shock absorbers

* The rear air springs

The ESC controls the damping mode selection according to the following factors:

* The vehicle speed

* The steering position

* The body to wheel displacement

The ESC module evaluates these inputs in order to separately control the shock absorbers, providing an enhanced ride and comfort level over the widest possible range of operating conditions.

Electronic Suspension Control Module

The electronic suspension control (ESC) module provides electronic control logic and output drive for each shock absorber. The ESC module makes decisions due to road and driving conditions based on various inputs. The ESC module receives input information by sensors that are directly connected to the ESC module or by other systems through the serial data line and uses these inputs to independently control the shock absorbers at each corner.

Electronic Suspension Control Position Sensors

The electronic suspension control (ESC) position sensors provide the ESC module with the body to wheel displacement input. The ESC module uses this and other inputs in order to control the stiffness of the shock absorber. If any body or wheel motion is detected, the ESC module will determine how soft or firm each shock absorber should be to provide the best ride. The ESC position sensors are mounted at each corner of the vehicle between the control arm and the body/frame.

Electronic Suspension Control Shock Absorber or Strut

The electronic suspension control (ESC) shock absorbers provide variable damping to resist suspension movement. The ESC shock absorber has the capability of providing multiple modes or values of damping forces, in both compression and rebound direction. The damping forces are modified utilizing electrical actuators located internally within the shock absorbers.

Electronic Suspension Control Operation

The electronic suspension control (ESC) system uses the information from other systems in order to execute certain functions.

The ESC system does not have a malfunction indicator lamp, but instead uses the instrument panel cluster (IPC) for the display functions. When the ESC system detects a malfunction that sets a DTC, the ESC system sends a message on the serial data line directly or through the powertrain control module (PCM) to the IPC, which will display one of the following messages:

* SHOCKS INOPERATIVE

* SERVICE SUSPENSION SYSTEM or SERVICE RIDE CONTROL

* SPEED LIMITED

The SHOCKS INOPERATIVE message will only be displayed if the ESC system detects a malfunction that sets a DTC and causes the ESC system to disable all 4 shock absorbers. The ESC system will send a message on the serial data line to the IPC to display this message.

The SERVICE SUSPENSION SYSTEM or SERVICE RIDE CONTROL message will only be displayed if the ESC system detects any malfunction that sets a DTC. The ESC system will send a message on the serial data line to the IPC to display this message.

The SPEED LIMITED message will only be displayed if the ESC system detects a malfunction that sets a DTC and causes the ESC system to disable all 4 shock absorbers. The ESC system will send a message on the serial data line to the PCM indicating that all 4 shock absorbers were disabled. The PCM then sends a message to the IPC to display this message.

The ESC module has the ability to store DTCs as current or history codes. Most ESC system malfunctions will display a message in the IPC and set a DTC. The message will remain ON until the RESET button is pressed on the driver information center (DIC). As long as the DTC is current, the message will be displayed after every ignition cycle and the RESET button must be pressed to bypass the message.

The ESC system uses an ignition cycling diagnostic approach in order to reduce the occurrence of false or intermittent DTCs that do not affect the functionality of the ESC system. This allows for the fail-soft actions to be taken whenever a malfunction condition is current, but requires the malfunction to be current for a certain number of ignition cycles before the corresponding malfunction code and message will be stored or displayed.

If the ESC detects a malfunction, the ESC system defaults with a fail-soft action. A fail-soft action refers to any specific action the ESC system takes in order to compensate for a detected malfunction. A typical ESC fail-soft action would be if the ESC system detects a malfunction with a shock absorber.

Automatic Level Control

The automatic level control (ALC) system maintains a desired rear suspension position under all types of loading conditions.

When the vehicle is unloaded, the rear suspension is at a desired position, which is monitored by the ESCM using the position sensor signal voltage inputs. As weight is added to the rear of the vehicle, the position sensor's signal voltage inputs change. When the ESCM detects a steady substantial change in the position sensor signal voltages for at least 10 seconds, it responds by commanding ON the compressor relay, which activates the compressor causing the air pressure in the air spring to inflate. This inflation raises the rear of the vehicle to regain the desired suspension position. When weight is removed from the vehicle, the ESCM responds by commanding ON the exhaust valve causing the air pressure in the air spring to deflate. This deflation lowers the vehicle to regain the desired suspension position.

The compressor is a positive displacement piston air pump driven by a 12-volt DC permanent magnet motor. The compressor draws filtered air through an intake line attached to an under body rail. The compressed air is then run through a dryer containing a moisture-absorbing chemical that dries the compressed air before it is sent to the air springs. Each time the compressor is activated, the ESCM commands ON the exhaust valve for 1.5 seconds to release air from the compression chamber in the compressor's cylinder head ensuring low motor current draw upon compressor activation. The ESCM also limits the amount of compressor run time to 180 seconds to protect the compressor components from thermal damage.

The ESCM has the ability to detect malfunctions within the ALC system. Any malfunctions detected will cause the DIC to display the SERVICE LEVELING SYSTEM message.