The Basics of a Town Car Suspension
The rear air suspension of a Town Car, is an air operated, computer controlled suspension system which replaces a conventional coil spring suspension with an airbag and provides low spring rates for improved ride and automatic REAR load leveling. It is standard on the Town Car and was an option on the Mercury Grand Marquis as well as the Ford Crown Victoria.
Two airbags replace the conventional steel springs and support the vehicle load at the rear wheels. Like most automotive applications, the air springs are a Rolling Lobe type design. The airbags are mounted onto the axle spring seats and to the frame upper spring seats, similar to the conventional rear steel spring system. Each airbag has its own solenoid that acts as a gate for air to go in or out. In other words, no air should go in or out of the airbag unless the solenoid has been opened by the module.
The suspension is operational in the run position and has limited operation for ONE HOUR after the ignition is turned to the off position.
The air suspension switch, located on the right side of the trunk, must be turned off when the vehicle is on a hoist, being towed, or when one side is off the ground (when changing a tire). The rear leveling system operates by adding or removing air in the springs to maintain the level of the vehicle at a predetermined height known as TRIM HEIGHT.
Air required for leveling the vehicle is distributed from the air compressor (underneath the air filter box) to the airbags by a single nylon air line which runs from the compressor dryer to the back of the car. The line is joined at a Y junction (just before the frame bends upwards on the drivers side) and splits 1 line into 2.
The Town Car is a 1-channel system. In other words, it has only one input for height sensing (1 sensor in the back) and in this case, the airbags are powered together. In other words, one airbag can't be open without the other. Because this system only has 1 sensor, it senses the height by an average between the two sides.
PULLING AIR SUSPENSION CODES ON THE TOWN CAR, GRAND MARQUIS & CROWN VICTORIA
(1990-1997)SUPER STAR II Tester 007-0041A must be used for this procedure
The absolute best way to find out whats going on with an Ford/Lincoln air suspension system, is to use a scan tool and retrieve any codes stored in the memory. Having the codes in the memory allows you to learn what fault(s) occured sometime in the past and depending on the system, will usually store these codes for 50 ignition cycles. When working on an intermittent problem, knowing the code(s) in the memory maybe the difference between fixing the problem and just guessing. This same scan tool can also be used to perform function tests which work great for Hard Fault problems that occur all the time.
This part of diagnostics is divided into three areas:
Auto/Manual Diagnostic Check
Diagnostic Trouble Code (DTC) Display
AUTO TEST DIAGNOSTICS
BEFORE TRYING TO RETRIEVE ANY CODES IN THE SYSTEM, YOU MAY WANT TO HAVE THE BATTERY & CHARGING SYSTEM CHECKED. A WEAK BATTERY WILL CAUSE ALL SORTS OF PROBLEMS IN THE AIR SUSPENSION. AUTOZONE AND A FEW OTHER AUTO PARTS STORES WILL USUALLY DO THIS FOR FREE
READ THIS FIRST
At the beginning of the automatic portion of the test, the control module checks for defective control module (DTC 70), for unstable battery voltage (DTC 80), then for shorted or open conditions that would create DTCs 39 through 46, and 68 through 71. If shorts or opens are detected, the automatic portion of the test is ended and a DTC 13 (Auto Test Failed) will be displayed on the SUPER STAR II tester. If no shorts or opens are detected, the automatic portion of the test continues. The control module attempts to raise and lower the vehicle to verify that the height sensor states (trim, high, and low) can be reached. A properly functioning vehicle will be at trim height at the end of the Auto Test. If all three states are not reached, the Auto Test will end and again a DTC 13 will be displayed. A DTC 12 will be displayed at the end of the Auto Test only if everything checked to this point is functional.
After the DTC 12 (or DTC 13) is displayed, the control module is ready to check for manual inputs. The manual inputs check the steering sensor and the door courtesy lamp switch circuits. During the manual test, the module continually monitors the door Circuit 159 or 24 and the steering sensor Circuits 633 and 634 Town Car, Circuits 834 and 835 Crown Victoria/Grand Marquis for activity. To pass the manual test the control module must detect that all four doors have been opened and closed, and that the steering wheel has been turned at least 1/4 turn in each direction. After the manual test, the STAR tester button must be toggled, or the control module will continue to monitor the manual test inputs indefinitely. Either a DTC 11 (Air suspension OK) or other DTCs will be displayed at this time.
After the Auto/Manual tests, the DTCs will be displayed automatically. Each DTC detected will be displayed for about 15 seconds. The code display will continue until all DTCs have been displayed. The display will repeat the DTC until the STAR test button is released (up). After all DTCs are written down, the pressed tester button may be released. DO NOT disconnect or turn OFF the tester. After this, the tester is ready to enter the Functional Test.
Lets get started
*Remove all extra loads from luggage and passenger compartments.
*Set STAR Tester as follows: STAR: EEC/MCU Setting
*SUPER STAR II: EEC/MCU Setting, FAST codes
*Turn ignition switch OFF.
*Turn air suspension switch (RH side of luggage compartment) OFF, then ON.
*Remove RH luggage compartment trim panel.
*Connect STAR Tester to data link connector. (NOTE: Ensure STAR test button is in HOLD (up) position before connecting to vehicle).
*Start engine. If engine cannot be started, connect battery charger to maintain battery level and turn ignition switch to RUN.
*Wait at least two seconds, then press STAR Tester button so it remains in the TEST (down) position.
*Within 20 seconds, a DTC 10 should be displayed.
*DTC 10 will be displayed for up to two minutes.
*DO NOT put any weight on vehicle while DTC 10 is displayed.
*When Auto Test is complete a DTC 12 (Auto Test passed) or DTC 13 (Auto Test failed) will be displayed.
*With DTC 12 or 13 displayed:
*Open and close all four doors sequentially.
*Turn steering wheel 1/4 turn in both directions.
NOTE: The above manual inputs can be done in any sequence.
*Release STAR TEST button to HOLD (up) position.
*Wait two seconds and press button to TEST (down) position.
*Within 20 seconds DTCs will be displayed
NOTE: The DTCs will be displayed for about 15 seconds each. After all DTCs have been displayed, the DTCs will be repeated. The DTCs will continue to repeat as long as the STAR tester button is in the TEST (down) position.
TOWN CAR SUSPENSION CODES
10=Diagnostics entered, auto test in progress
12=auto test passed, perform manual inputs
13=auto test failed, perform manual inputs
15=no drive cycle errors detected
16=EVO diagnostic trouble code(electronic variable orifice)
17-EVO diagnostic trouble code
18=EVO diagnostic code
23=Function test, vent rear
26=function test, compress rear
28=steering wheel switch not detected (town car only)
31=function test, air compressor relay toggle
32=function test, vent solenoid toggle
33=function test, air spring solenoid toggle
35=ERASE CODES IN MEMORY
39=compressor relay control circuit short to ground
40=compressor or relay control circuit short to ground
42=air spring solenoid short to ground
43=air spring solenoid short to battery
44=vent solenoid short to battery
45=short in vent solenoid circuit
46=air suspension height sensor supply circuit shorted
51=unable to detect lowering of rear
54=unable to detect raising of rear
68=short in rear height sensor circuit
70=replace control module
71=height sensor open circuit
72=did not detect 4 open & closed door signals
74=EVO diagnostic trouble code
80=control module detects low battery voltage
Functional Tests are used in some of the DTC Pinpoint Tests to aid in system diagnosis.
The Functional Test mode can only be entered after Auto Test has been performed. A DTC 11 or any other DTCs must be displayed before the Functional Test mode can be entered.
Release Star Tester button to the HOLD (up) position.
Wait at least 20 seconds.
Press Star Tester button to the TEST (down) position.
DTC 23 should be displayed, then DTCs 26, 31, 32 and 33 will be displayed in order. Each DTC will be displayed for about 15 seconds. After all the DTCs are displayed, they will be repeated as long as the Star Test button is in TEST (down) position.
DTC 23: Vent Rear - During this test the control module will attempt to open the vent solenoid valve and air spring solenoid valves (5311) as long as the Star tester button is pressed. The rear of the vehicle will lower.
NOTE: DTC 26 is normally used to inflate the air spring after installation.
DTC 26: Compress Rear - During this test the control module will attempt to energize the compressor and open the spring solenoid valves as long as the Star tester button is pressed. The rear of the vehicle will rise.
NOTE: The extended use of this test can cause the self-resetting circuit breaker in the compressor to open. If this happens, allow the compressor to cool down for 15 minutes. Then, restart the diagnostic procedures.
DTC 31: Air Compressor Relay Toggle - During this test, the control module will attempt to cycle the compressor relay ON for one second and OFF for one second repeatedly. This cycle will repeat for as long as the Star tester button is pressed. The compressor will be heard cycling ON and OFF if this test is successful.
DTC 32: Vent Solenoid Valve Toggle - During this test, the vent solenoid valve is opened for one second, then closed for one second. This cycle will repeat for as long as the Star tester button is pressed. The vent solenoid valve in the air compressor will be heard cycling ON and OFF if this test is successful.
DTC 33: Air Spring Solenoid Valve Toggle - During this test, both air spring solenoid valves will be opened for one second, then closed for one second repeatedly. This cycle will repeat for as long as the Star tester button is pressed. The control module cannot turn one spring solenoid valve on without turning the other solenoid valve on (Circuits 114 (BR/PK) and 115 (T/W) are tied together inside the control module). To verify that both solenoid valves operate, raise the vehicle on a hoist. Do not turn the air suspension switch OFF. Remain in Functional Test DTC 33. Then, touch each solenoid valve to verify that it is cycling ON and OFF.
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