Suspension Control System - Suspension Leveling Cadillac STS I

Fastener Tightening Specifications

Fastener Tightening Specifications

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Scheme 2

Scheme 3

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Scheme 5

Automatic Level Control Suspension Connector End Views

Automatic Level Control (ALC) Compressor Connector End Connector Part Information OEM: 12129565 Service: 15306069 4-Way F Metri-Pack 280 Series, Sealed (GY) Terminal Part Information Terminal: Terminal Seal: Release Tool: Core Crimp: Insulation Crimp: Test Probe: Pin Wire Color Circuit No. Function A WH 320 Automatic Level Control Exhaust Solenoid Control B D-GN 322 Automatic Level Control Compressor Motor Supply Voltage C RD/BK 1342 Battery Positive Voltage D BK 1050 Ground

Diagnostic Starting Point - Automatic Level Control

Begin the system diagnosis with Diagnostic System Check - Vehicle in Vehicle DTC Information. The Diagnostic System Check will provide the following information

1. The identification of the control module which command the system.
2. The ability of the control module to communicate through the serial data circuit.
3. The identification of any stored diagnostic trouble codes (DTCs) and their status.

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.

Scan Tool Output Controls

Scan Tool Output Controls

Scan Tool Data List

Scan Tool Data List

Automatic Level Control Scan Tool Data Definitions

The Automatic Level Control (ALC) Scan Tool Data Definitions contains a brief description of all scan tool parameters.

Circuit Description

The automatic level control exhaust solenoid valve is switched ON or OFF by the electronic suspension control (ESC) module. The ESC module provides a ground whenever exhaust activity is required and during a head-relief sequence which occurs before each compressor start-up. This drive output from the ESC module is continually monitored to determine if the voltage level agrees with the commanded state.

DTC Descriptor

This diagnostic procedure supports the following DTC

DTC C0660 Level Control Exhaust Valve Circuit

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC C0660

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC

The following conditions must be present to set the DTC

1. The ESC module detects voltage less than a preset value in the exhaust solenoid control circuit during an exhaust solenoid valve OFF state test.
2. The ESC module detects voltage greater than a preset value in the exhaust solenoid control circuit during an exhaust solenoid valve ON state test.
3. The fault is detected during 3 consecutive ignition cycles, or during the same ignition cycle after clearing the DTC with a scan tool.

Action Taken When the DTC Sets

1. ALL rear leveling activity for the remainder of the ignition cycle will be disabled.
2. The SERVICE SUSPENSION SYSTEM message will be displayed.

Conditions for Clearing the MIL/DTC

1. The scan tool can be used to clear the DTC.
2. The DTC is saved as history when the ESC module no longer sees an out of range voltage condition in the exhaust solenoid control circuit. The DTC will clear if the fault does not return after 50 consecutive ignition cycles.

Diagnostic Aids

These DTCs are set only by electrical problems with the electronic level control (ELC) exhaust solenoid control circuit. Pneumatic blockage problems do not set these DTCs.

A temporary compressor overload, such as high head pressure during a cold start, may cause the ELC fuse to open. This is one possible cause of DTC C0662.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step tests for voltage in the automatic level control (ALC) exhaust solenoid control circuit.
2. 3: This step tests for a short to voltage in the ALC exhaust solenoid control circuit.
3. 4: This step tests for voltage in the battery positive voltage circuit of the ALC compressor in order to isolate a short to ground or an open.

DTC C0660

The Automatic Level Control (ALC) System uses a relay to control compressor activity. The ignition 3 circuit provides battery voltage to the coil side of the ALC compressor relay. The electronic suspension control (ESC) module circuitry provides a switched path to ground controlling the compressor relay. This circuit is also monitored to determine if the voltage level agrees with the commanded state.

This diagnostic procedure supports the following DTC

DTC C0712 Level Control Compressor Relay Circuit

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC C0712

The ignition is ON.

The following conditions must be present to set the DTC

1. The ESC module detects voltage less than a preset value in the compressor motor control circuit during a compressor OFF state test.
2. The ESC module detects voltage greater than a preset value in the compressor motor control circuit during a compressor ON state test.
3. The fault is detected during three consecutive ignition cycles, or during the same ignition cycle after clearing the DTC with a scan tool.

1. The ESC disables the ALC relay for the remainder of the ignition cycle.
2. The SERVICE SUSPENSION SYSTEM message will be displayed.

1. The scan tool can be used to clear the DTC.
2. The DTC is saved as history when the ESC module no longer sees an out of range voltage condition in the compressor motor control circuit. The DTC will clear if the fault does not return after 50 consecutive ignition cycles.

These DTCs are set only by electrical problems with the ALC compressor relay coil circuit. Compressor motor problems and pneumatic leakage problems do not set these DTCs.

The numbers below refer to the step numbers on the diagnostic table.

1. 2: Tests for voltage in the Automatic Level Control relay coil supply voltage circuit.
2. 3: Tests for a short to voltage in the Automatic Level Control relay coil supply voltage circuit.

DTC C0712

Symptoms - Automatic Level Control

Review the system operation in order to familiarize yourself with the system functions. Refer to Automatic Level Control Description and Operation (w/ F55) .

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the automatic level control suspension. Refer to «Checking Aftermarket Accessories»(/cadillac/sts/i-2004-2007/remont/body-electrical/#wiring-systems-electrical-power-management-introduction__checking-aftermarket-accessories) in Wiring Systems.
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
3. Inspect for binding or damaged shock absorbers.

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

1. «Air Compressor Leak Test»(/cadillac/sts/i-2004-2007/remont/electronic-suspension/#suspension-control-system-suspension-leveling__air-compressor-leak-test)
2. «Automatic Level Control System Leak Test»(/cadillac/sts/i-2004-2007/remont/electronic-suspension/#suspension-control-system-suspension-leveling__automatic-level-control-system-leak-test)
3. «Rear of Vehicle High»(/cadillac/sts/i-2004-2007/remont/electronic-suspension/#suspension-control-system-suspension-leveling__rear-of-vehicle-high)
4. «Rear of Vehicle Low»(/cadillac/sts/i-2004-2007/remont/electronic-suspension/#suspension-control-system-suspension-leveling__rear-of-vehicle-low)

Air Compressor Leak Test

Tools Required

1. J 22124-B Pressure Gage (0-300 psi). See «Special Tools»(/cadillac/sts/i-2004-2007/remont/electronic-suspension/#suspension-control-system-suspension-leveling__special-tools) .
2. J 22124-91 Pressure Gage Adapter. See «Special Tools»(/cadillac/sts/i-2004-2007/remont/electronic-suspension/#suspension-control-system-suspension-leveling__special-tools) .

1. Attach the J 22124-91 pressure gage adapter to the air dryer. See «Special Tools»(/cadillac/sts/i-2004-2007/remont/electronic-suspension/#suspension-control-system-suspension-leveling__special-tools) .
2. Attach the J 22124-B pressure gage to the J 22124-91 pressure gage adapter with the toggle valve on the opposite side of the air compressor. See «Special Tools»(/cadillac/sts/i-2004-2007/remont/electronic-suspension/#suspension-control-system-suspension-leveling__special-tools) . Close the toggle valve.
3. Apply air pressure at the Schrader valve. Pressurize until the J 22124-B pressure gage reads 690 kPa (100 psi). See «Special Tools»(/cadillac/sts/i-2004-2007/remont/electronic-suspension/#suspension-control-system-suspension-leveling__special-tools) .
4. Check the following areas using soap bubbles: Solenoid valve - Replace the air compressor head if leaking. Air dryer to compressor head O-ring - Replace the air dryer if leaking. Air dryer cover - Replace the air dryer if leaking. Air compressor head gasket - Replace the air compressor head if leaking. Air compressor head cover gasket - Tighten the cover bolts to 5.6 N.m (50 lb in) if the head cover gasket is leaking. If the leak persists, replace the air compressor head.

Automatic Level Control System Leak Test

Automatic Level Control System Leak Test

Rear of Vehicle High

Rear of Vehicle High

Rear of Vehicle Low

Rear of Vehicle Low

Removal Procedure

1. Raise and support the vehicle. Refer to «Lifting and Jacking the Vehicle»(/cadillac/sts/i-2004-2007/remont/hoistjack/#general-information) in General Information.
2. Remove the compressor assembly. Refer to «Air Compressor Replacement»(/cadillac/sts/i-2004-2007/remont/electronic-suspension/#suspension-control-system-suspension-leveling) .
3. Remove the hose (1) from the air dryer (2).
4. Remove the mounting screw (1).
5. Rotate the air dryer (1) to remove from compressor.

Installation Procedure

1. Install the air dryer (1) to the compressor.
2. Install the air dryer mounting screw (1). Tighten: Tighten the bolts to 6 N.m (53 lb in).
3. Install the hose (1) onto the air dryer (2).
4. Install the compressor to the vehicle. Refer to «Air Compressor Replacement»(/cadillac/sts/i-2004-2007/remont/electronic-suspension/#suspension-control-system-suspension-leveling) .
5. Lower the vehicle.

1. Raise and support the vehicle. Refer to «Lifting and Jacking the Vehicle»(/cadillac/sts/i-2004-2007/remont/hoistjack/#general-information) in General Information.
2. Remove the tire and wheel. Refer to «Tire and Wheel Removal and Installation»(/cadillac/sts/i-2004-2007/remont/wheel-tire-system/#tires-and-wheels) in Tires and Wheels.
3. Disconnect the front ride sensor link from the upper control arm ball stud.
4. Disconnect the front ride sensor harness connector.
5. Loosen the front ride sensor retaining nut.
6. Gently tap the front ride sensor retaining stud in order to loosen the stud to fender connection.
7. Remove the front ride sender from the vehicle.

1. Position the sensor to the vehicle.
2. Install the front ride sensor retaining nut. Tighten: Tighten the nut to 9 N.m (80 lb in).
3. Connect the front ride sensor link to the upper control arm ball stud.
4. Connect the front ride sensor harness connector.
5. Install the tire and wheel. Refer to «Tire and Wheel Removal and Installation»(/cadillac/sts/i-2004-2007/remont/wheel-tire-system/#tires-and-wheels) in Tires and Wheels.
6. Lower the vehicle.

1. Raise and support the vehicle. Refer to «Lifting and Jacking the Vehicle»(/cadillac/sts/i-2004-2007/remont/hoistjack/#general-information) in General Information.
2. Remove the tire and wheel. Refer to «Tire and Wheel Removal and Installation»(/cadillac/sts/i-2004-2007/remont/wheel-tire-system/#tires-and-wheels) in Tires and Wheels.
3. Disconnect the rear ride sensor link from the upper control arm ball stud.
4. Disconnect the rear ride sensor harness connector.
5. Loosen the rear ride sensor retaining nut.
6. Gently tap the rear ride sensor retaining stud in order to loosen the stud to fender connection.
7. Remove the rear ride sender from the vehicle.

1. Install the sensor to the vehicle.
2. Bottom out the captured stud in the key hole.
3. Rotate the sensor and bracket until the tab on the bracket bottoms out in the slot.
4. If the sensor bracket is not yet level, continue to rotate it allowing the captured stud to lift slightly from the bottom of the keyhole, until the sensor is level.
5. Install the rear ride height sensor retaining nut. Tighten: Tighten the nut to 9 N.m (80 lb in).
6. Connect the ride sensor link to the upper control arm ball stud.
7. Connect the ride sensor harness connector.
8. Install the tire and wheel. Refer to «Tire and Wheel Removal and Installation»(/cadillac/sts/i-2004-2007/remont/wheel-tire-system/#tires-and-wheels) in Tires and Wheels.
9. Lower the vehicle.

1. Raise and support the vehicle. Refer to «Lifting and Jacking the Vehicle»(/cadillac/sts/i-2004-2007/remont/hoistjack/#general-information) in General Information.
2. Twist the air tube seal connection on the rear shocks.
3. Disconnect the air tube from the rear shock absorber.
4. Disconnect the exhaust system from the rear exhaust hangers. Support the exhaust.
5. Remove the automatic level control compressor with the bracket attached. Refer to «Air Compressor Replacement»(/cadillac/sts/i-2004-2007/remont/electronic-suspension/#suspension-control-system-suspension-leveling) .
6. Disconnect the air tube from the right wheel house liner clip.
7. Remove the wheelhouse liner screw in order to position the liner to access the air tube.
8. Remove the air tube from the frame at the right wheel house liner.
9. Remove the fuel filler neck bolt and reposition the air tubes.
10. Remove the air tubes from the vehicle.

1. Install the air tubes to the vehicle.
2. Position the air tubes at the fuel filler neck.
3. Install the fuel filler neck bolt. Refer to «Filler Tube Replacement»(/cadillac/sts/i-2004-2007/remont/testing-diagnostics/#engine-control-system-36l-ly7-introduction) in Engine Controls - 3.6L or «Filler Tube Replacement»(/cadillac/sts/i-2004-2007/remont/testing-diagnostics/#engine-control-system-46l-lh2-introduction) in Engine Controls - 4.6L.
4. Install the air tubes to the frame at the right wheelhouse liner.
5. Install the right wheelhouse liner screw. Refer to «Wheelhouse Liner Panel Replacement - Rear»(/cadillac/sts/i-2004-2007/remont/exterior-body-panels/#body-rear-end) in Body Rear End.
6. Connect the air tube to the right wheel house liner clip.
7. Install the automatic level control (ALC) compressor with bracket. Refer to «Air Compressor Replacement»(/cadillac/sts/i-2004-2007/remont/electronic-suspension/#suspension-control-system-suspension-leveling) .
8. Connect the exhaust system to the rear exhaust hangers. Remove the exhaust support.
9. Connect the air tube to the rear shocks.
10. Lower the vehicle.

1. Raise and support the vehicle. Refer to «Lifting and Jacking the Vehicle»(/cadillac/sts/i-2004-2007/remont/hoistjack/#general-information) in General Information.
2. Disconnect the exhaust system from the rear exhaust hangers.
3. Remove the automatic level control (ALC) compressor bracket mounting bolts.
4. Carefully lower the ALC compressor assembly.
5. Twist the air tube at the ALC compressor clamp.
6. Disconnect the air tube from the ALC compressor.
7. Disconnect the ALC electrical harness connector.
8. Remove the ALC compressor bracket side mounting nut.
9. Remove the ALC compressor with the bracket from the vehicle.
10. Remove the ALC compressor top bracket mounting screw.
11. Remove the electrical harness connector from the ALC bracket.
12. Disconnect the bleed hose from the clip.
13. Remove the ALC bracket to ALC compressor screws.
14. Remove the ALC bracket from the ALC compressor.

1. Position the ALC bracket to the ALC compressor
2. Install the ALC bracket to ALC compressor screws. Tighten: Tighten the screws to 9 N.m (80 lb in).
3. Connect the bleed hose to the clip.
4. Install the electrical connector to the ALC compressor bracket.
5. Connect the air tube to the ALC compressor.
6. Connect the ALC electrical harness connector.
7. Install the ALC bracket side mounting nut.
8. Install the ALC bracket mounting bolts. Tighten: Tighten the bolts to 9 N.m (80 lb in).
9. Connect the exhaust system the rear exhaust hangers.
10. Lower the vehicle.

General Description

The Automatic Level Control (ALC) system automatically adjusts the rear height of the vehicle in response to changes in vehicle loading.

The ALC system consists of the Electronic Suspension Control module, 2 position sensors, an air compressor assembly, an ALC compressor relay, an intake hose and filter, an air tube, and 2 rear shock absorbers. The air compressor assembly consists of an air compressor and an air dryer mounted on a bracket. The air compressor head is a replaceable part of the air compressor. The exhaust solenoid is a non-replaceable part of the air compressor head.

The vehicles rear vertical height is measured by the 2 position sensors. These 2 position sensors convert this rear height measurement into an analog voltage which is read by the ESC module. The ESC module then determines what action exhaust, compress, or no action shall take place. To compress, the ESC module switches the ELC compressor relay to ground.

The compressor is activated when the ignition is on, and weight is added to the vehicle. The exhaust solenoid is connected directly to the battery (+), enabling the system to exhaust with the ignition on or off when excess weight is removed.

Raising the Vehicle

When a load is added to the vehicle, the vehicle body moves down causing the sensor actuating arm to rotate upward. The upward arm movement activates an internal timing circuit and, after an initial fixed delay, the ESC module provides a ground to complete the compressor relay circuit. The battery positive circuit to the compressor is then complete and the compressor runs, sending pressurized air to the shock absorbers through the air tubes.

As the shock absorbers inflate, the vehicle body moves upward rotating the actuating arm towards its original position. Once the body reaches its trim height, the compressor relay circuit is opened and the compressor is turned off.

Air Compressor Head Relief Sequence

In order to reduce current draw during air compressor starting, the ESC module performs an air compressor head relief sequence before air compressor operation. This sequence reduces the air pressure in the air compressor cylinder during start-up. The air compressor head relief sequence occurs as follows

1. Exhaust solenoid is activated.
2. Air compressor is activated 1.3 seconds after the exhaust solenoid is activated.
3. Exhaust solenoid is de-activated 0.5 seconds after the air compressor is activated.

Lowering the Vehicle

When a load is removed from the rear of the vehicle, the body rises, causing the sensor actuating arm to rotate downward. This again activates the internal timing circuit. After the initial fixed delay, the ESC module provides a ground to complete the exhaust solenoid circuit, activating the solenoid. Now, air starts exhausting out of the shock absorbers, back through the air dryer and exhaust solenoid valve, and into the atmosphere.

As the vehicle body lowers, the actuating arm rotates to its original position. When the vehicle body reaches its trim height, the exhaust solenoid is deactivated, which closes the exhaust solenoid and prevents air from escaping.

Air Replenishment Cycle

An air replenishment cycle (ARC) is commanded after each ignition-ON cycle. The purpose of the ARC is to ensure that the ALC system is operating at or above minimum air pressure. The ARC occurs as follows

1. The EXHAUST SOLENOID IS ACTIVATED 20 seconds after the ignition has been turned on.
2. The AIR COMPRESSOR IS ACTIVATED 1.3 seconds after the exhaust solenoid is energized.
3. The EXHAUST SOLENOID IS DE-ACTIVATED 0.5 seconds after the air compressor is activated.
4. The AIR COMPRESSOR IS DEACTIVATED 3.2 seconds after the exhaust solenoid is de-energized.

Air Compressor Description

The air compressor is a positive displacement air pump, powered by a 12 volt DC permanent-magnet motor. The air compressor head contains intake and exhaust ports plus a solenoid-operated exhaust valve that releases air from the ALC system when activated. Air compressor intake air is drawn through an intake air hose and filter, mounted in the body rail. The air compressor is a serviceable part and is mounted on a bracket. The bracket is mounted to the underbody behind the right rear wheel well.

Air Dryer Description

The air dryer is attached to the air compressor head assembly at the pressure outlet and provides a dual function

1. It contains a moisture-absorbing desiccant chemical that absorbs moisture from the compressed air before it is delivered to the rear struts. Moisture is removed from the air dryer and returned to the atmosphere when air is exhausted out of the struts during lowering.
2. It contains valving that maintains a system residual pressure of 48 to 97 kPa (7 to 14 psi). This system pressure is maintained for improved ride characteristics and improved air sleeve reliability.

Exhaust Solenoid Description

The exhaust solenoid is a non-serviceable part of the air compressor head and provides a dual function

1. When activated, it exhausts air from the rear struts.
2. It acts as a relief valve to limit the maximum air pressure output of the compressor.

Automatic Level Control Sensor Description

The 2 position sensors that are utilized by the ALC system are mounted on the body, one sensor over each upper control arm of the rear suspension. Each rear position sensor has a link that is connected to corresponding rear suspension upper control arm.

The ESC module provides supply voltage of 5 volts and ground to the position sensors. The position sensors then supply an analog output voltage of 0.35 to 4.75 volts back to the ESC control module. The amount of voltage is dictated by the vertical height of the rear of the vehicle.

Air Shock Absorber or Strut Description

The rear air adjustable shock absorbers are constructed with a rubber-like air sleeve attached to the dust tube and reservoir. This sleeve forms a flexible chamber which extends the shock absorber when pressure in the chamber is increased. When air pressure is reduced, the weight of the vehicle collapses the shock absorber. In order to maintain proper operation and reliability of the air adjustable shock absorbers, a system pressure from 48-97 kPa (7-14 psi) must be maintained at all times.

Air Lines and Connectors Description

The air tube is a non-serviceable item consisting of the following

1. One connector at the ALC air dryer
2. Two tubes between the ALC air dryer and the 2 rear shock absorbers
3. Two connectors with spring clips, 1 at each rear shock absorber

At the rear shock absorbers, the air tube connectors are held on with spring clips which snap into the grooves of the shock absorber air fittings. Air tube connectors are sealed using 2 O-rings.

Although the tubes are flexible, care should be taken not to kink them and to keep them from contacting the exhaust system.

Special Tools

Special Tools Illustration Tool Number/ Description J 22124-B Pressure Gage J 22124-91 Pressure Gage Adaptor J 34142-B 12-V Unpowered Test Lamp Tech 2

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Scheme 7

Scheme 8

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See also:
• Diagnostic System Check - Vehicle
• DTC Symptom Description
• Circuit Testing
• Wiring Repairs
• Testing for Intermittent Conditions and Poor Connections
• Connector Repairs
• Control Module References
• Checking Aftermarket Accessories
• Shock Absorber Replacement
• Lifting and Jacking the Vehicle
• Fastener Notice
• Tire and Wheel Removal and Installation
• Filler Tube Replacement
• Filler Tube Replacement
• Wheelhouse Liner Panel Replacement - Rear
• Automatic Level Control Suspension Schematics
• Air Compressor Leak Test
• Automatic Level Control System Leak Test
• Rear of Vehicle High
• Rear of Vehicle Low
• Special Tools
• Symptoms - Automatic Level Control