Suspension Control ( Automatic - Electronic ): Description and Operation
DESCRIPTIONFig. 1 Automatic Leveling System. 1989 Lincoln Town Car, 1989-91 Crown Victoria & Grand Marquis:
The automatic level control system, Fig. 1, is used on 1989 Lincoln Town Car, 1989-91 Crown Victoria and Grand Marquis models and is an addition to the standard rear suspension system and adjusts the vehicles trim height with varying vehicle loads automatically.
The system consists of air adjustable rear shocks, a compressor assembly, air dryer with minimum retention valve, exhaust solenoid, compressor relay, rotary height sensor, microcomputer, connecting wiring and nylon tubing.
SYSTEM OPERATING MODES
Ignition switch in Off position
The system will operate for approximately 30 minutes after the ignition switch is turned from the Run to the Off position. Then, the system is inoperable through the microcomputer. The system will allow down requests only (lower vehicle) as required during the 30 minutes except that the exhaust control is suspended after continuous ON operation for one minute. Turning the ignition switch to ON position resets the operation. If the sensor arm moves to a neutral or low position, this function is also reset and normal ignition Off venting control resumes.
Ignition switch in Run position (less than 10 seconds)
The system will not allow any requests from the height sensor for the first 10 seconds, although requests are monitored continuously and stored in the microcomputer control memory.
Ignition switch in Run position (more than 10 seconds)
The leveling system is activated when weight is added to or removed from the rear of the vehicle to maintain the rear of the vehicle level at a predetermined rear suspension height. This is known as the vehicle's trim height. Trim height is controlled by the height sensor. Distance of the body to ground will change with tire size and inflation pressure. When load is added to the vehicle, the body is forced downward, causing the height sensors actuating arm to rotate upward (low-out-of-trim), generating two sensor signals to the control module. After a continuous height sensor of approximately 7 to 13 seconds (time delay), the module activates the air compressor (through a relay), sending air to the adjustable rear shock absorbers through the nylon tubing. As the body raises, the height sensor actuator arm continues rotating downward until the pre-set trim height is obtained. The air compressor is turned Off by the control module.
A similar action takes place whenever weight is removed. The body raises causing the sensor actuator arm to rotate downward (high, out-of-trim), generating two sensor signals to the control module. After a continuous high sensor signal of 7 to 13 seconds (time delay), the module opens the vent solenoid. As the body lowers, the sensor actuating arm is rotated upward until its pre-set trim is obtained. The module then closes the vent solenoid which prevents further air from escaping.
Air required for raising or lowering the vehicle is distributed from the compressor by one nylon air line which is connected between the compressor dryer and the LH air shock absorber, which has a dual port quick connect fitting. A second nylon air line starts here and connects to the RH air shock absorber. The air lines are color coded to identify which air shock they attach to. Shock-to-shock air lines are color coded, natural. Shock-to-compressor air lines are color coded blue on except station wagon models or yellow on station wagon models.
Fig. 2 Automatic Leveling System Wiring Diagram/Connectors (Part 1 Of 2):
Fig. 2 Automatic Leveling System Wiring Diagram/Connectors (Part 2 Of 2):
Referring to Fig. 2, electrical power to operate the load leveling system is distributed by the main body wiring harness. The wiring harnesses involved, and their function in the leveling system, are as follows:
1. 14401-Provides an extension of the ignition switch circuit 298 (ignition switch in Run position input to the control module).
2. 14A435-Supplies battery power to system. Directly connects to the air compressor motor, air compressor relay and control module.
3. 12614-Directly connects to the rotary height sensor, compressor motor, relay, vent solenoid, and the control module.
The compressor relay and compressor vent solenoid incorporate internal diodes for electrical noise suppression and are polarity sensitive. Ensure care is taken when servicing these components as not to switch the battery feed (positive) and ground (negative) circuits or serious component and/or system damage will result.
After turning the ignition switch to the Run position, if any upward or downward requests cannot be allowed within 2 minutes (compressor run time out) and 1 minute vent time out, the module controls are suspended. Reset operation occurs by cycling the ignition switch from Off to Run positions.