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Home >> Lincoln >> 1997 >> Mark VIII Base >> Repair and Diagnosis >> Suspension >> Electronic Suspension >> Suspension - Electronic Air >> Self-Diagnostic Tests >> DTC 99: Unable To Detect Raising Or Lowering Of One Or More Corners >> Control Module Operation

Control Module Operation

Control module uses output voltage from height sensors to determine ride height of vehicle. If control module senses a corner is too high, it applies battery voltage to vent solenoid and spring solenoid for that corner. If control module does not receive a change in output for height sensor, DTC 99 will be stored in control module memory.

  1. Inspect Vehicle

    Look for corners that are obviously lower or higher than trim height. Always repair low corner before repairing high corner. If a corner is too low, repair and go to next step. If a corner is too high, repair and go to step  3. If all corners are about trim height, go to DTC 98 .

  2. Pump Low Corners

    Turn air suspension off. Perform Function Test on suspect corner pump (LF is 212, RF is 214, LR is 216 and RR is 218). See FUNCTION TEST . If air spring is low on pressure, it may take 1.0-1.5 minutes for spring to raise. If compressor does not run, go to DTC 75 . If vehicle starts to raise, go to step  4.

  3. Vent High Corners

    Turn air suspension off. Perform appropriate Function Test to vent high air spring (LF is 213, RF is 215, LR is 217 and RR is 219). See FUNCTION TEST . If air spring has a very high pressure, it may take up to one minute for corner to begin to lower. If suspect corner goes down, height sensor may be out of range, go to DTC 50  for LF, DTC 55  for RF, or DTC 60  for LR. If suspect corner does not go down, go to step  11.

  4. Inspect Ball Stud Brackets

    Turn air suspension off. Position vehicle over a lube pit or alignment rack. Inspect height sensors and mounting brackets. If ball stud and/or brackets are damaged or height sensors are off ball studs, replace and/or repair components as necessary. If there is no damage and height sensors are in place, go to next step.

  5. Test For Open Height Sensor Ground

    Turn air suspension off. Disconnect accessible end of height sensor from ball stud. Enter Function Test for trim detection and audible output for suspect height sensor (LF is 223, RF is 224 and LR is 225). See FUNCTION TEST . Slowly move sensor over full range of travel, completing a full stroke in approximately 5 seconds. If frequency of tone pulses remains constant, go to DTC 50  for LF, DTC 55  for RF, or DTC 60  for LR. If tone pulses are not constant, install sensor to ball stud and go to next step.

  6. Check For Blocked Air Lines

    Inspect air lines for kinks etc. Disconnect air line from suspect spring solenoid and compressor air drier. Attach hand vacuum pump to air line and draw vacuum. If vacuum can be drawn and held, locate and repair kink or pinch in air line. If air line does not hold vacuum, go to next step.

  7. Open In Air Line

    Install air line to air spring. Attach vacuum pump to drier side of suspect air line. If vacuum can be drawn and held, go to next step. If vacuum cannot be held, locate and repair open in air line and repeat Auto Test.

  8. Check Air Spring Solenoid

    Attach shop air supply to drier end of suspect air line and spring assembly. Perform Function Test to open suspect spring solenoid (LF is 213, RF is 215, LR is 217 and RR is 219). See FUNCTION TEST . Inflate air spring to full up travel. If air flows into suspect air spring and there are no leaks, go to next step. If air does not flow into spring and/or there is a leak, replace air spring solenoid or leaking air spring. Restore system and repeat Auto Test.

  9. Check Compressor For Output & Leaks

    Reconnect air line to drier. Remove right front air spring line at spring solenoid. Connect line to pressure gauge having at least a 0-200 psi (0-14.1 kg/cm2 ) range. Perform Function Test No. 221. Within 30 seconds, pressure gauge should reach at least 130 psi (9.1 kg/cm2 ). Stop Function Test No. 221. Pressure gauge should hold pressure until relieved by vent (Function Test No. 213, 215, 217 or 219) or until gauge is disconnected. If compressor output reaches 130 psi (9.1 kg/cm2 ) but does not hold, locate and repair leak in drier. If compressor output does not reach 130 psi (9.1 kg/cm2 ), go to next step. If compressor output reaches 130 psi (9.1 kg/cm2 ) and holds, compressor is okay.

  10. Check Drier & Compressor Assembly

    Remove drier canister from compressor assembly. Use care not to lose or damage "O" ring on nose of drier canister. Blow shop air through disconnected air line port. If air flows freely through drier canister, replace compressor assembly. If air does not flow freely through drier canister, replace drier canister. Restore system and repeat Auto Test.
    11. WARNING: Vehicle may drop quickly when performing this procedure.

  11. Check Air Flow Between Spring & Drier
    Disconnect air line to suspect air spring at drier canister. Perform Function Test to open suspect spring solenoid (LF is 213, RF is 215, LR is 217 and RR is 219). See FUNCTION TEST . If corner of vehicle lowers, go to step  12. If corner of vehicle does not lower, go to step 14).

  12. Check For Blocked Air Lines

    Inspect air lines for kinks etc. Disconnect air line from suspect spring solenoid and compressor air drier. Attach hand vacuum pump to air line and draw vacuum. If vacuum can be drawn and held, locate and repair kink or pinch in air line. If air line does not hold vacuum, go to next step.

  13. Check For Stuck Solenoid Valve

    Reconnect air line to air spring solenoid. Attach air drier end of air line to shop air. Perform Function Test to open suspect spring solenoid (LF is 213, RF is 215, LR is 217 and RR is 219). See FUNCTION TEST . If air does not flow into spring, replace spring solenoid. If air flows into spring and vehicle raises, air lines or solenoid may be contaminated causing an intermittent condition. Check system operation
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