For 1990-2009 cars

### Raising Vehicle

The vehicle body is forced downward when a load is added to the vehicle. This load causes the sensor actuating arm to rotate upward. The upward movement of the sensor actuating arm activates the internal timing circuit. The sensor completes the compressor circuit to ground after an initial delay of 25 seconds. With the compressor circuit complete, the compressor runs, taking in air through the air compressor filter and sending the air through the tubing to the shock absorbers. As the shock absorbers inflate, the rear of the vehicle moves upward, rotating the sensor actuating arm back toward the original position prior to the load addition. The sensor opens the compressor circuit and shuts off the compressor once the body reaches the original height +/- 19 mm (+/- 0.75 in).

### Lowering Vehicle

The body is forced upward when an excess load is removed from the rear of the vehicle. This causes the sensor actuating arm to rotate downward. The downward rotation of the actuating arm activates the internal timing circuit. The sensor completes the solenoid valve circuit to ground after an initial delay of 25 seconds. With the solenoid valve energized, the air begins to exhaust out of the shock absorbers back through the air dryer, the solenoid valve, the air compressor filter and into the atmosphere. The sensor actuating arm rotates upward toward the original position as the rear of the vehicle lowers. When the vehicle body reaches the original height +/- 19 mm (+/- 0.75 in), the sensor opens the solenoid circuit. This de-energizes the solenoid valve, which prevents any further air from escaping.

### Air Replenishment Cycle (ARC)

The air replenishment cycle ensures that the shock absorbers are filled with at least the minimum residual pressure. The sensor commands an air replenishment cycle each time the ignition switch is turned on. Sensor position is checked when the ignition switch is turned on. If the sensor indicates that the vehicle does not need raising or lowering, an internal timer circuit is activated. After a 35 to 40 second delay, the compressor is turned on for approximately 4 seconds. This ensures that the shock absorbers are filled with adequate residual pressure.

If weight is added to, or removed from, the vehicle during the initial 35 to 40 second delay, the air replenishment cycle will be overridden and the vehicle will raise or lower after the normal delay.

### Compressor Head Relief

A 1.5 second actuation of the exhaust solenoid valve occurs each time the compressor is to start in order to ensure the low compressor motor starting current. The 1.5 second actuation of the exhaust solenoid valve reduces the air pressure in the compressor head cavity.

### Vehicle Speed Input

The ALC system uses vehicle speed input from the electronic brake traction control module/brake pressure modulator valve (EBTCM/BPMV) assembly in order to change the vehicle leveling response time.

When the vehicle is stationary, the response time of the intake or the exhaust control switch is 3 seconds. When the vehicle is moving faster than 1 km/h (0.62 mph), the response time of the intake or the exhaust control switch is 25 seconds.