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

Rear of Vehicle Low w/o Road Sensing Suspension

Step

Action

Value(s)

Yes

No

DEFINITION: The rear of the vehicle will not raise, is always low, or leaks down when the vehicle is not used. 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?

--

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?

--

Go to Step 3

Go to Step 4

3

Correct the condition.

Is the condition corrected?

--

Go to Automatic Level Control System Operation Check

--

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?

--

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 or reset complete?

--

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 the link properly connected and in good condition?

--

Go to Step 8

Go to Step 7

7

Reconnect 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 the vehicle is 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 switch to the ON position.
  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 struts to inflate.

--

Go to Step 10

Go to Step 12

10

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 11

11

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

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 switch to the ON position.
  3. Connect a fused jumper from the height sensor connector (vehicle side) terminal B to ground.

Is the air compressor operating?

--

Go to Height Sensor Operational Check

Go to Step 14

14
  1. Turn the ignition switch to the OFF position.
  2. Connect the height sensor electrical connector.
  3. Remove the ALC relay from the rear compartment relay center #2.
  4. Turn the ignition switch to the ON position.
  5. Measure the voltage from terminal A3 to ground.

Is the measurement within the specified values?

10.5-15 V

Go to Step 16

Go to Step 15

15

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

Is the replacement or repair complete?

--

Go to Automatic Level Control System Operation Check

--

16

Measure the voltage from terminal A1 to ground (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 circuit condition in CKT 1340 (ORN) between the ALC MaxiFuse® block and the rear compartment relay center #2.

Is the repair complete?

--

Go to Automatic Level Control System Operation Check

--

18
  1. Connect a voltmeter between the terminals where relay pins 85 and 86 were removed.
  2. Turn the ignition switch to the ON position. NOTE: The ignition switch must be cycled if the ignition was left on from the previous step.

Is the measurement within the specified values after 17 to 27 seconds.

10.5-15 V

Go to Step 20

Go to Step 19

19

Check for a poor connection at the height sensor connector, terminal B, or an open-circuit condition in CKT 321 (YEL).

Was a poor connection or open-circuit condition found and corrected?

--

Go to Automatic Level Control System Operation Check

Go to Height Sensor Operational Check

20

Connect a 30-amp fused jumper between terminals A1 and B3.

Is the air compressor operating?

--

Go to Step 21

Go to Step 22

21

Replace the ELC 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.

Is the measurement within the specified values?

10.5-15 V

Go to Step 24

Go to Step 23

23

Repair the open-circuit condition in CKT 322 (DK GRN).

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 the same connector, terminal D.

Is the measurement within the specified values?

10.5-15 V

Go to Step 26

Go to Step 25

25

Repair the open-circuit condition in CKT 1050 (BLK).

Is the repair complete?

--

Go to Automatic Level Control System Operation Check

--

26
  1. Disconnect the jumper and install the ALC relay.
  2. Jumper the air compressor connector (compressor side), terminal D, to ground.
  3. Jumper the air compressor connector (compressor side), terminal B to B+ using a 30-amp fused jumper wire.

Is the air compressor operating?

--

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

Check the following:

    • Rear struts for a leaking air sleeve. NOTE: If the air sleeve is worn through, perform the Residual Air Pressure Check .
    • Air tube for kinks or pinched tubes.
    • Air tubes for a disconnected condition
    • All air tube connections using soap and water.

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-B adapter tube to the air dryer.
  3. Connect the J 22124-B gage to the J 22124-B adapter tube with the toggle valve on the opposite side (away from the air compressor) and closed.
  4. Disconnect the air compressor electrical connector.
  5. Jumper the air compressor electrical connector (compressor side), terminal A to ground.
  6. Jumper the air compressor electrical connector (compressor side), terminal C, to B+ using a 30-amp fused jumper wire.
  7. Allow the air compressor to operate until the pressure reaches 690 kPa (100 psi).
  8. Disconnect the jumper from terminal A when 690 kPa (100 psi) is reached.

Is the air compressor able to reach it 690 kPa (100 psi)?

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 stay at 690 kPa (100 psi)?

690 kPa (100 psi)

Go to Step 32

Go to Air Compressor Leak Test

32

The air tube or a shock absorber is leaking.

Replace the component with the leak.

Is the replacement complete?

--

Go to Automatic Level Control System Operation Check

--

Rear of Vehicle Low 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.

Does the air compressor come on within 30 seconds?

30 seconds

Go to Step 9

Go to Step 3

3
  1. Turn the ignition OFF.
  2. Disconnect the ALC connector from the ALC air compressor assembly.
  3. Disconnect connector C1 from the CVRSS control module.
  4. Turn the ignition ON.
  5. Connect pin C15 of CVRSS connector C1 (harness side) to ground using a jumper wire.
  6. Measure the voltage between pin B of the ALC air compressor connector (harness side) and ground.

Does the voltmeter display a voltage greater than 10 volts?

10 volts

Go to Step 4

Go to Step 7

4
  1. Remove the jumper wire from pin C15.
  2. Turn the ignition OFF.
  3. Check for continuity between pin D of the ALC air compressor connector (harness side) and ground.

Is there continuity?

--

Go to Step 6

Go to Step 5

5
  1. Turn the ignition OFF.
  2. Repair the open circuit condition in CKT 1050.

Is the repair complete?

--

Go to Automatic Level Control System Operation Check

--

6
  1. Replace the ALC air compressor assembly. Refer to Air Compressor Replacement .
  2. Replace the air tube. Refer to Air Tube Replacement .

Is the repair complete?

--

Go to Step 12

--

7
  1. Remove the jumper wire from pin C15.
  2. Turn the ignition OFF.
  3. Check for the following:
    4. • tripped (open) ALC circuit breaker
    • blown (open) IGN-0-BODY fuse
    • open CKT 322
    • open CKT 321
    • open CKT 1340
    • open CKT 147

Was a problem found?

--

Go to Step 8

8

Repair the open circuit condition or reset/replace the circuit breaker/fuse. NOTE: A tripped circuit breaker may indicate:

    • no head relief - check for CVRSS codes
    • faulty air compressor
    • a short to ground in CKT 1340

Is the repair complete?

--

Go to Automatic Level Control System Operation Check

9

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

Are any damaged sensors or disconnected links present?

--

Go to Step 13

Go to Step 10

10

Perform the ALC System Leak Test.

Is a leak present?

--

Go to Step 11

Go to Step 12

11

Repair the leak in the ALC System.

Is the repair complete?

--

Go to Step 14

--

12
  1. Turn the ignition OFF.
  2. Connect the scan tool to the DLC.
  3. Turn the ignition ON with 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 14

--

13

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

Is the replacement complete?

--

Go to Automatic Level Control System Operation Check

--

14
  1. Reconnect all of the connectors that were removed.
  2. Clear the CVRSS DTCs. Refer to Clearing DTCs .
  3. Wait for at least 5 minutes.

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

--

System OK

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