GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 1999 🢒 Aurora 🢒 Suspension 🢒 Automatic Level Control 🢒 Rear of Vehicle Low

Step

Action

Value(s)

Yes

No

1

Is any aftermarket equipment installed on the vehicle that could affect the ALC system?

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Go to Step 2

Go to Step 4

2

Inspect the aftermarket equipment to ensure that it is not affecting ALC performance.

Is the aftermarket equipment affecting the ALC performance?

--

Go to Step 3

Go to Step 4

3

Correct the condition.

Is the condition corrected?

--

Go to Automatic Level Control System Operation Check

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4

Inspect the ELC fuse and the HVAC CONT fuse for an open fuse.

Is the fuse open?

--

Go to Step 5

Go to Step 6

5

Important: If the fuse is open repeatedly, check CKT 41 (BRN) or CKT 340 (ORN) for a short to ground.

Replace the fuse.

Is the replacement complete?

--

Go to Automatic Level Control System Operation Check

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6

Inspect the height sensor and link for proper connection or damage.

Are the height sensor and the link properly connected and in good condition?

--

Go to Step 8

Go to Step 7

7

Repair or replace the height sensor or the link. Refer to Automatic Level Control Sensor and Bracket Replacement .

Is the repair or replacement complete?

--

Go to Automatic Level Control System Operation Check

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8

Does the vehicle leak down when not used for an extended period of time (overnight), but then come up to normal trim height with vehicle use?

--

Go to Step 28

Go to Step 9

9
  1. Turn the ignition ON.
  2. Add approximately 300 lbs of weight to the rear of the vehicle.

Does the rear of the vehicle rise and not leak down? NOTE: Allow 27 seconds for the air compressor to start and then additional time for the shock absorbers to inflate.

--

Go to Step 10

Go to Step 12

10

Measure the trim height at the rear underbody points. Refer to Trim Height .

Is the trim height correct?

--

Go to Automatic Level Control System Operation Check

Go to Step 11

11

Adjust the height sensor. Refer to Automatic Level Control Sensor Adjustment .

Is the adjustment complete?

--

Go to Automatic Level Control System Operation Check

--

12

Did the air compressor operate when weight was added?

--

Go to Step 28

Go to Step 13

13
  1. Disconnect the height sensor electrical connector.
  2. Turn the ignition ON.
  3. Connect a fused jumper from the height sensor connector (vehicle side) terminal B to ground.

Did the air compressor operate?

--

Go to Height Sensor Operational Check

Go to Step 14

14
  1. Turn the ignition OFF.
  2. Connect the height sensor electrical connector.
  3. Remove the ALC relay from the LH rear fuse block.
  4. Turn the ignition ON.
  5. Measure the voltage from the terminal where relay pin 85 was removed, to ground, with a DMM.

Is the measurement within the specified values?

10.5-15 V

Go to Step 16

Go to Step 15

15

Repair the open in CKT 41.

Is the repair complete?

--

Go to Automatic Level Control System Operation Check

--

16

Measure the voltage from the terminal where relay pin 30 was removed, to ground, with a DMM (this terminal is hot at all times).

Is the measurement within the specified values?

10.5-15 V

Go to Step 18

Go to Step 17

17

Repair the open in CKT 340 between the RH and LH rear fuse blocks.

Is the repair complete?

--

Go to Automatic Level Control System Operation Check

--

18
  1. Turn the ignition OFF.
  2. Connect a DMM between the terminals where relay pins 85 and 86 were removed.
  3. Turn the ignition ON.

Is the measurement within the specified values after 17 to 27 seconds (17 to 27 seconds is the height sensor delay period).

10.5-15 V

Go to Step 20

Go to Step 19

19

Inspect for a poor connection at the height sensor connector, terminal B, or an open in CKT 321.

Was a poor connection or an open found and repaired?

--

Go to Automatic Level Control System Operation Check

Go to Height Sensor Operational Check

20

Connect a 30-amp fused jumper between the terminals where relay pins 30 and 87 were removed.

Did the air compressor operate?

--

Go to Step 21

Go to Step 22

21

Replace the ALC relay.

Is the replacement complete?

--

Go to Automatic Level Control System Operation Check

--

22
  1. Leave the jumper from the previous step in place.
  2. Disconnect the air compressor electrical connector.
  3. Measure the voltage from the air compressor electrical connector (vehicle side), terminal B to ground, with a DMM.

Is the measurement within the specified values?

10.5-15 V

Go to Step 24

Go to Step 23

23

Repair the poor connection or the open in CKT 322.

Is the repair complete?

--

Go to Automatic Level Control System Operation Check

--

24
  1. Leave the jumper from the previous step in place.
  2. Measure the voltage from the air compressor connector (vehicle side), terminal B to terminal D, with a DMM.

Is the measurement within the specified values?

10.5-15 V

Go to Step 26

Go to Step 25

25

Repair the open in :

    • (OLDS) - circuit 1250
    • (BUICK) - circuit 1050

Is the repair complete?

--

Go to Automatic Level Control System Operation Check

--

26
  1. Disconnect the jumper.
  2. Install the ALC relay.
  3. Connect a jumper from the air compressor connector (compressor side), terminal D to ground.
  4. Connect a 30-amp fused jumper from the air compressor connector (compressor side), terminal B to B+.

Did the air compressor operate?

--

Go to Step 13

Go to Step 27

27

Replace the air compressor. Refer to Air Compressor Replacement .

Is the replacement complete?

--

Go to Automatic Level Control System Operation Check

--

28

Inspect the following:

    • Rear shock absorbers for a leaking air sleeve. NOTE: If the air sleeve is worn through, perform the residual air pressure check. Refer to Residual Air Pressure Check .
    • Air tube for kinks or pinched tubes.
    • Air tubes for loose connections at the shock absorbers or at the air dryer.
    • All air tube connections for leaks using a soap and water solution.

Was a leak or damage found and corrected?

--

Go to Automatic Level Control System Operation Check

Go to Step 29

29
  1. Disconnect the air tube from the air dryer.
  2. Connect the J 22124-91 to the air dryer.
  3. Connect the J 22124-B to the J 22124-91 with the toggle valve on the opposite side (away from the air compressor) and closed.
  4. Disconnect the air compressor electrical connector.
  5. Connect a jumper from the air compressor electrical connector (compressor side), terminal D to ground.
  6. Connect a 30-amp fused jumper from the air compressor electrical connector (compressor side), terminal B, to B+.
  7. Allow the air compressor to operate until the pressure reaches the specified value.
  8. Disconnect the jumper from terminal D.

Did the pressure reach the specified value?

690 kPa (100 psi)

Go to Step 31

Go to Step 30

30

Replace the air compressor. Refer to Air Compressor Replacement .

Is the replacement complete?

--

Go to Automatic Level Control System Operation Check

--

31

Does the air pressure reading on the J 22124-B remain steady at the specified value?

690 kPa (100 psi)

Go to Step 32

Go to Air Compressor Leak Test

32
  1. Open the J 22124-B toggle valve.
  2. Disconnect the vehicle air tube from the LH rear shock absorber.
  3. Connect the J 22124-B adapter tube to the LH rear shock absorber and to the J 22124-B .
  4. Connect a jumper from the air compressor connector, terminal D, to ground (terminal B should still be connected to B+).
  5. Allow the air compressor to operate until the pressure reaches the specified value.
  6. Disconnect the jumper from terminal D.

Did the pressure reach the specified value?

690 kPa (100 psi)

Go to Step 34

Go to Step 33

33

Replace the LH rear shock absorber. Refer to Shock Absorber Replacement .

--

Go to Automatic Level Control System Operation Check

--

34
  1. Disconnect the adapter tube from the LH rear shock absorber.
  2. Connect the vehicle air tube to the LH rear shock absorber.
  3. Disconnect the vehicle air tube from the RH rear shock absorber.
  4. Connect the adapter tube to the RH rear shock absorber.
  5. Connect a jumper from the air compressor connector, terminal D, to ground (terminal B should still be connected to B+).
  6. Allow the air compressor to operate until the pressure reaches the specified value.
  7. Disconnect the jumper from terminal D.

Did the pressure reach the specified value?

690 kPa (100 psi)

Go to Step 36

Go to Step 35

35

Replace the RH rear shock absorber. Refer to Shock Absorber Replacement .

Is the replacement complete?

--

Go to Automatic Level Control System Operation Check

--

36
  1. Disconnect the adapter tube from the RH rear shock absorber and the J 22124-B . Do not connect the vehicle air tube.
  2. Disconnect the J 22124-91 from the air dryer and the J 22124-B .
  3. Connect the vehicle air tube to the air dryer.
  4. Connect the J 22124-B to the vehicle air tube at the RH rear shock absorber. The J 22124-B toggle valve must be on the side of the gage away from the air tube.
  5. Close the J 22124-B toggle valve.
  6. Connect a jumper from the air compressor connector, terminal D, to ground (terminal B should still be connected to B+).
  7. Allow the air compressor to operate until the pressure reaches the specified value.
  8. Disconnect the jumper from terminal D.

Did the pressure reach and maintain the specified value?

690 kPa (100 psi)

Go to Step 38

Go to Step 37

37

Replace the air tube. Refer to Air Tube Replacement .

Is the replacement complete?

--

Go to Automatic Level Control System Operation Check

--

38

Inspect the rear shock absorbers for binding or damage.

Was a binding or damaged shock absorber found?

--

Go to Step 39

System OK

39

Replace the binding or damaged shock absorber. Refer to Shock Absorber Replacement .

Is the replacement complete?

--

Go to Automatic Level Control System Operation Check

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