Suspension control (auto-elec)
Lowering the Vehicle
When a load is removed from the vehicle, the vehicle body is moved upward. When the Automatic Level Control (ALC) Sensor has detected a "Car-High" state for 7-14 seconds , the Exhaust Control Switch is closed to ground. With CKT 320 grounded, the Exhaust Solenoid is energized allowing the Exhaust Valve to open. The ALC System vents into the atmosphere, lowering the rear of the vehicle. When the vehicle body reaches its original height of +25 mm (+1 inch) , the Sensor opens the Exhaust Control Switch, de-energizing the Solenoid and closing the Exhaust Valve.
Raising the Vehicle
When a load is added to the vehicle, the vehicle body is moved downward. When the Automatic Level Control (ALC) Sensor has detected a "Car-Low" state for 7-14 seconds , the Intake Control Switch is closed to ground. With CKT 321 grounded, the coil in the Compressor Motor relay is energized and the relay contacts close. Battery voltage is applied to the Compressor Motor, which operates the Compressor and pumps air into the adjustable shock absorbers. As the shocks extend, the rear of the vehicle rises. When the vehicle body reaches its original height of +25 min (+1 inch) , the ALC Sensor opens the Intake Control Switch, de-energizing the Relay coil and the Compressor Motor stops.
Automatic Level Control (Alc)
The Automotive Control keeps the rear of the vehicle at a constant height. If weight is added to the vehicle the Automatic Level Control (ALC) Sensor turns on the ALC Air Compressor. Air pumped into the shock absorbers until the ALC Sensor senses that the vehicle is level. An Actuator Arm is linked between the upper RH Control Arm and the Sensor, which is mounted to the rear crossmember of the frame. It turns as the vehicle height changes. The Sensor detects this motion and operates switches to control the air flow into and out of the shock absorbers.
Voltage is applied. at all time the Compressor by Underhood Electrical Centre Fuse #1 and to the Sensor by I/P Fuse block Fuse #27. This allows the ALC System to vent after a load is removed. Voltage is also applied to the Sensor by I/P Fuse block Fuse #12, with the ignition Switch in "RUN," "BULB TEST" or "START."
To ensure that the shock absorbers are filled with adequate residual pressure, the Compressor Motor will run for 3 to 5 seconds , approximately 35 to 50 seconds after the Ignition Switch is turned to "RUN."
The Sensor must detect a "Car-Low" or "Car-High" state for 7-14 seconds before activating the intake or exhaust outputs. This prevents system operation during normal ride motions. In addition, the Sensor limits Compressor Motor run time or Exhaust Solenoid energized time to a maximum of 4.5 to 7 minutes .
This time limit is necessary to prevent continuous Compressor Motor operation in case of a severe system leak or continuous vent. Cycling the Ignition Switch to "OFF" and back to "RUN" resets the 4.5 to 7 minute maximum run timer.
The Automatic Level Control (ALC) and Electronic Level Control (ELC) system adjusts rear trim height in response to changes in vehicle loading. This system consists of an air compressor assembly, air dryer, exhaust solenoid, compressor relay, height sensor, air adjustable shocks and air tubing. The compressor is activated when the ignition is On and weight is added to the vehicle. The exhaust solenoid is connected directly to the positive side of the battery, allowing the system to exhaust when the ignition is Off and excess weight is removed.
When a load is added to the vehicle, the body is moved down causing the height sensor arm to rotate upward. This movement activates the internal timing circuit which, after a predetermined delay of 8-15 seconds, grounds pin No. 3, thus completing the compressor relay circuit to ground. When the relay circuit is energized, the circuit to the compressor is complete, allowing the compressor to send pressurized air to the shocks.
As the shocks inflate, the vehicle body moves upward, causing the sensor arm to rotate downward. Once the body reaches its original height, the sensor opens the compressor relay circuit and shuts the compressor Off.
When excess load is removed from the rear of the vehicle, the body rises upward, which causes the sensor arm to rotate downward. This movement activates the internal timing circuit which, after a predetermined delay of 8-15 seconds, allows the sensor to complete the exhaust solenoid circuit to ground. With the solenoid energized, air exhausts from the shocks back through the air dryer and exhaust solenoid valve.
As the vehicle body lowers, the height sensor arm is rotated upward until the vehicle reaches its original height. When this height is reached, the sensor opens the exhaust solenoid circuit which prevents air from escaping.
The height sensor position is checked when the ignition is turned On. If the height sensor indicates that it is not necessary to raise or lower the vehicle, the internal timer circuit is activated. After 40 seconds, the compressor will run for four seconds. This ensures the shocks are filled with the proper residual pressure (7-14 psi). If weight is added or removed from the vehicle during this 40 second delay, the air replenishment cycle will be overridden and the vehicle will raise or lower after normal delay.
PERFORM BEFORE BEGINNING SYSTEM DIAGNOSIS
Check Underhood Electrical Center Fuse #1. If Fuse #1 is open, check for a short to ground in CKT 1040.
Check I/P Fuse Block Fuse #12. If Fuse #12 is open, check for a short to ground in CKT 639.
Check I/P Fuse Block Fuse #27. If Fuse #27 is open, check for a short to ground in CKT 740.
Check that G102 and G300 are clean and tight.
If ALC Air Compressor runs continuously for approximately 7 minutes , check system air hoses for cracks or leaks.
Check for a broken (or partially broken) wire inside of the insulation which could cause system malfunction but prove "GOOD" in a continuity/voltage check with a system disconnected. These circuits may be intermittent or resistive when loaded, and if possible, should be checked by monitoring for a voltage drop with the system operational (under load).
Check for proper installation of aftermarket electronic equipment which may affect the integrity of other systems (refer to General Troubleshooting Procedures ). See: Diagrams\Diagnostic Aids
Refer to System Diagnosis .
Vehicle must be on a level surface, doors closed, with no passengers or extra weight in car.
If any RTD rear position or rear damper codes are set, they must be repaired before performing trim height adjustment procedure.
Check rear position sensor values in diagnostics (RTD Data Parameters SD13 and SD14) to be sure they are within normal value ranges. If not, check for bent position sensor brackets or disconnected sensors.
Check fuel level reading in IPC (Data Parameter ID40) and round up to the nearest gallon (example, 12.1 gallons rounds up to 13 gallons).
Connect Tech 1 to Data Line Connector (DLC).
Key on, engine off. Important: Do not sit in vehicle while performing trim set procedure.
Proceed per instructions on Tech 1 readout.
When complete, remove Tech 1 from vehicle.