GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 1999 🢒 Eldorado 🢒 Suspension 🢒 Road Sensing Suspension (RSS) 🢒 Rear of Vehicle High

Rear of Vehicle High w/o Road Sensing Suspension

Step

Action

Value(s)

Yes

No

DEFINITION: The rear of the vehicle is above trim height. This diagnostic procedure only applies to vehicles without Road Sensing Suspension.

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

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

Is the aftermarket equipment affecting the ALC performance?

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Go to Step 3

Go to Step 4

3

Correct the condition.

Is the condition corrected?

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Go to Automatic Level Control System Operation Check

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4

Check the ELC fuse in the rear compartment fuse Block and the ALC circuit breaker in the ALC MaxiFuse Block® for an open (blown) or tripped (open) condition.

Is the fuse open or the circuit breaker tripped?

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Go to Step 5

Go to Step 6

5

Replace the fuse or reset the circuit breaker. NOTE: If the fuse is open (blown) repeatedly, check CKT 2141 (BRN) for a short circuit to ground condition. If the circuit breaker trips repeatedly, check CKT 1340 (ORN) for a short circuit to ground condition.

Is the replacement complete?

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Go to Automatic Level Control System Operation Check

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6

Check the height sensor and link for proper connection and damage.

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

--

Go to Step 8

Go to Step 7

7

Reconnect or replace the height sensor or 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
  1. Turn the ignition switch to the ON position.

    2. Important: The vehicle must be raised on a drive-on lift or be supported at the rear under the rear axle. Full vehicle weight must be on the rear suspension.

  2. Raise the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
  3. Disconnect the link from the height sensor. Refer to Automatic Level Control Sensor and Bracket Replacement .
  4. Move the height sensor lever down so that it is approximately 45 degrees below level (to the floor) and hold it there.

Will the rear of the vehicle lower to trim level or below? NOTE: The height sensor has a 17 to 27 second delay period before the exhaust solenoid is activated.

--

Go to Step 9

Go to Step 10

9

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

Is trim height at the rear underbody points correct? Refer to Trim Height in Suspension General Diagnosis.

--

Go to Automatic Level Control System Operation Check

Repeat this Step

10

Move the height sensor lever up so that it is approximately 45 degrees above level (to the floor) and hold it there for a minimum of 27 seconds (17 to 27 seconds is the height sensor delay period).

Does the air compressor come on?

--

Go to Step 11

Go to Height Sensor Operational Check

11

Disconnect the air tube from the air dryer.

Will the rear of the vehicle lower to trim level or below?

--

Go to Step 19

Go to Step 12

12
  1. Connect the link to the height sensor lever.
  2. Disconnect the air tube from both struts.

Will the rear of the vehicle lower to trim level or below?

--

Go to Step 13

Go to Step 14

13

Replace the air tube. Refer to Air Tube Replacement .

Is the replacement complete?

--

Go to Automatic Level Control System Operation Check

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14

Is the vehicle uneven (more than 12 mm (0.5 in) from side to side at the rear?

--

Go to Step 16

Go to Step 15

15

Replace both rear springs. Refer to Coil Spring Replacement in Rear Suspension.

Is the trim height at the rear underbody points correct? Refer to Trim Height in Suspension General Diagnosis.

--

Go to Automatic Level Control System Operation Check

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16
  1. Note which side of the vehicle is high.
  2. Bounce the rear of the vehicle three times.

Is the vehicle still uneven more than 12 mm (0.5 in) from side to side at the rear?

--

Go to Step 17

Go to Step 18

17

Replace the rear spring on the side of the vehicle that is high. Refer to Coil Spring Replacement in Rear Suspension.

Is the trim height at the rear underbody points correct? Refer to Trim Height in Suspension General Diagnosis.

--

Go to Automatic Level Control System Operation Check

Go to Step 1

18

Replace the rear shock absorber on the side of the vehicle that is high. Refer to Shock Absorber Replacement in Rear Suspension.

Is the trim height at the rear underbody points correct? Refer to Trim Height in Suspension General Diagnosis.

--

Go to Automatic Level Control System Operation Check

Go to Step 1

19
  1. Raise the rear of the vehicle up as much as possible by holding the height sensor up. NOTE: The height sensor has a 17 to 27 second delay period before the air compressor is activated.
  2. Reconnect the link to the height sensor.
  3. Disconnect the air compressor electrical connector.
  4. Check for continuity between terminals C and A of the air compressor connector.

Is continuity present?

Continuity

Go to Step 21

Go to Step 20

20

Replace the air compressor head. Refer to Automatic Level Control Air Compressor Head Replacement .

Is the replacement complete?

--

Go to Automatic Level Control System Operation Check

--

21

Measure the voltage between the air compressor electrical connector (vehicle side), terminal C and ground.

Is the measurement within the specified values?

10.5-15 V

Go to Step 23

Go to Step 22

22

Repair the open circuit condition in CKT 2141 (BRN).

Is the repair complete?

--

Go to Automatic Level Control System Operation Check

--

23
  1. Cycle the ignition switch and return it to the ON position.
  2. Measure the voltage from the air compressor electrical connector (vehicle side), terminal C to the same connector, terminal A. NOTE: The link must be connected. Voltage will not be present within 17 to 27 seconds of the ignition switch cycle (height sensor delay). Voltage will not be present after approximately seven minutes.

Is the measurement within the specified values?

10.5-15 V

Go to Step 25

Go to Step 24

24

Check for an open circuit condition in CKT 320 (WHT). Also, check for a poor connection at the height sensor connector.

Was an open circuit or poor connection found and repaired?

--

Go to Automatic Level Control System Operation Check

Go to Height Sensor Operational Check

25

Replace the air compressor head. Refer to Automatic Level Control Air Compressor Head Replacement .

Is the replacement complete?

--

Go to Automatic Level Control System Operation Check

--

Rear of Vehicle High with Road Sensing Suspension

Step

Action

Value(s)

Yes

No

1

Was the ALC System Check performed?

--

Go to Step 2

Go to Automatic Level Control System Operation Check

2
  1. Turn the ignition ON with the engine OFF.
  2. Listen for the ALC air compressor to activate.

Is the ALC air compressor running for more than 5 minutes?

5 minutes

Go to Step 3

Go to Step 6

3
  1. Turn the ignition OFF
  2. Remove the ALC compressor relay.
  3. Turn the ignition ON with the engine OFF.

Is the air compressor running?

--

Go to Step 4

Go to Step 5

4
  1. Turn the ignition OFF.
  2. Reinstall the ALC compressor relay.
  3. Repair the short to voltage in CKT 322.

Is the repair complete?

--

Go to Step 13

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5
  1. Turn the ignition OFF.
  2. Replace the ALC compressor relay.

Is the replacement complete?

--

Go to Step 13

--

6

Inspect the left and right rear position sensors for damage and disconnected links.

Are any damaged sensors or disconnected links present?

--

Go to Step 7

Go to Step 8

7

Replace the damaged rear position sensor or reconnect the link. Refer to Electronic Suspension Rear Position Sensor Replacement .

Is the replacement complete?

--

Go to Step 13

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8
  1. Remove the ALC intake filter from the vehicle body (do not remove it from the ALC air compressor or hose). Refer to Automatic Level Control Air Compressor Air Filter Replacement .
  2. Using the scan tool, cycle output ALC compressor.
  3. After 1 minute, stop cycling.
  4. Cycle the ALC exhaust while checking to see if air is exiting the ALC intake air filter.

Is air exiting the ALC intake air filter?

--

Go to Step 11

Go to Step 9

9
  1. Stop exhausting.
  2. Disconnect the air tubes from both rear shock absorbers. Refer to Air Tube Replacement .
  3. Connect the J 22124-B gage to both (between) the air tubes.
  4. Open the J 22124-B gage toggle valve.
  5. Disconnect the air tube from the ALC air dryer. Refer to Air Tube Replacement .
  6. Apply shop air to the J 22124-B gage schrader valve.

Is air exiting both of the air tubes at the ALC air dryer connection?

--

Go to Step 10

Go to Step 12

10
  1. Turn the ignition OFF.
  2. Replace the ALC air compressor assembly. Refer to Air Compressor Replacement .
  3. Install the ALC intake air filter on the vehicle body. Refer to Automatic Level Control Air Compressor Air Filter Replacement .

Are all of the replacements and/or installations complete?

--

Go to Step 13

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11
  1. Turn the ignition OFF.
  2. Connect the scan tool.
  3. Turn the ignition ON with the engine OFF.
  4. Perform the ALC Trim Height Adjustment. Refer to Trim Height Adjustment .

Has the ALC Trim Height Adjustment been completed?

--

Go to Step 13

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12

Replace the air tube going from the air dryer to both the rear shock absorbers. Refer to Air Tube Replacement .

Is the replacement complete?

--

Go to Step 13

--

13
  1. Turn the ignition OFF.
  2. Turn the ignition ON with the engine OFF.
  3. Wait for at least 5 minutes.

Is the rear of the vehicle trim (level)? Refer to Trim Height in Suspension General Diagnosis.

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System OK

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