Suspension - Rear Electronic Level Control Buick Roadmaster VIII

DESCRIPTION

Electronic Level Control (ELC) system automatically adjusts rear of vehicle to correct riding height (curb height), compensating for load added to or removed from vehicle.

System consists of air adjustable shock absorbers, air drier, air filter, air lines, compressor, compressor relay, exhaust solenoid valve and height sensor.

SYSTEM OPERATION

If riding height decreases due to weight being added to vehicle, height sensor arm assembly rotates upward in relation to height sensor. This activates a timing circuit in height sensor. After a delay of about 8-15 seconds, height sensor grounds compressor relay, turning on air compressor. Delay prevents system from operating during normal changes in riding height which occur while driving. Air is then pumped into air adjustable shock absorbers, raising vehicle. As vehicle rises, height sensor arm assembly rotates downward. When vehicle rises to curb height, height sensor opens ground circuit to compressor relay, turning compressor off.

When riding height increases due to weight being removed from vehicle, height sensor arm assembly rotates downward. This activates timing circuit in height sensor. After a delay of about 8-15 seconds, height sensor arm assembly grounds exhaust solenoid valve circuit, energizing exhaust solenoid valve. Air is then vented from air adjustable shock absorbers, lowering vehicle. As vehicle is lowered, height sensor arm assembly rotates upward. When vehicle has lowered to curb height, height sensor opens exhaust solenoid valve circuit, closing exhaust solenoid valve.

Each time ignition is turned on, height sensor commands an air replenishment cycle which maintains at least minimum pressure in air adjustable shock absorbers. If height sensor determines vehicle is at curb height, a timer circuit is activated. After a delay of about 35-40 seconds, compressor turns on for about 4 seconds to ensure residual system pressure exists. Air drier maintains a minimum air pressure of 8-14 psi (.56-.98 kg/cm 2 ) in air adjustable shock absorbers. If riding height changes during 35-40 second delay, air replenishment cycle will be overridden and system will raise or lower vehicle after normal delay.

Voltage is available at compressor and height sensor at all times. This allows system to vent after load is removed with ignition turned off. Height sensor limits compressor operation or exhaust solenoid valve energized time to 4.5-7.0 minutes. Time limit prevents continuous compressor operation in case of air leak. Turning ignition from off to on will reset compressor operation or exhaust solenoid valve energized time.

When voltage is supplied to compressor, exhaust solenoid valve is simultaneously activated for 1.5 seconds. This relieves pressure in compressor cylinder head, reducing amount of current required to start compressor.

Air Adjustable Shock Absorber

Air adjustable shock absorber is a conventional shock absorber enclosed in an air chamber which extends when air pressure is increased.

Air Drier

Air drier, attached to compressor output, absorbs moisture from air that is delivered to air adjustable shock absorbers. Air drier contains a valve that maintains a minimum shock absorber air pressure of 8-14 psi (.56-.98 kg/cm 2 ).

Compressor

Compressor, mounted on rear crossmember, provides air pressure for system operation.

Compressor Relay

Compressor relay is mounted to compressor bracket. When compressor relay is grounded by height sensor, power is supplied to compressor.

Exhaust Solenoid Valve

Exhaust solenoid valve, located in compressor head assembly, exhausts air from the system and limits compressor output pressure.

Height Sensor

Height sensor, mounted to rear crossmember, links the body to rear axle. Height sensor controls ground circuits of compressor relay and exhaust solenoid valve, and limits the operation of these components to 7 minutes.

Note. Adjust height sensor if rear riding height is not 10.4" (264 mm). (Scheme 5) Height sensor arm assembly can be moved a total of 5 degrees. One degree of change at height sensor arm assembly results in a 1/4" (6 mm) change in height at rear bumper.

Raise and support vehicle. Ensure link is securely connected to height sensor metal arm before adjusting height sensor. Loosen lock bolt securing metal arm to plastic arm. (Scheme 1) To increase riding height, move plastic arm upward. To lower riding height, move plastic arm downward. Tighten lock bolt.

Scheme 1

SYSTEM OPERATION TEST

Note. Before performing system operation test, visually inspect height sensor, height sensor electrical connector and sensor-to-axle link for damage.

1. Place vehicle on flat surface with heavy items removed from passenger and luggage compartments. Measure distance between floor and a suitable spot on rocker panel, just forward of rear wheelwell opening. This distance is unloaded height. Turn ignition on. Add 300 lbs. (136 kg) of weight to rear of vehicle. If compressor starts within 8-15 seconds, go to step 4).
2. If compressor does not start within 8-15 seconds, and vehicle is within 1.00" (25.4 mm) of unloaded height (distance measured in step 1), perform «AIR DRIER TEST»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control__air-drier-test) under COMPONENT TESTING.
3. If compressor does not start within 8-15 seconds, and vehicle is not within 1" (25.4 mm) of unloaded height, adjust height sensor, and then retest system. See «HEIGHT SENSOR»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control) under ADJUSTMENTS. If compressor still does not start within 8-15 seconds, go to «COMPRESSOR INOPERATIVE»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control__compressor-inoperative) under ELECTRICAL TESTING.
4. If compressor stops within 7 minutes, go to next step. If compressor runs continuously, perform «HEIGHT SENSOR TEST»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control__height-sensor-test) under COMPONENT TESTING.
5. If system leaks down, perform «COMPRESSOR LEAK TEST»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control__compressor-leak-test) under COMPONENT TESTING. If vehicle returns to within 1" (25.4 mm) of unloaded height, go to step 7).
6. If vehicle does not return to within 1" (25.4 mm) of unloaded height, adjust height sensor, and retest system. See «HEIGHT SENSOR»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control) under ADJUSTMENTS. If vehicle still does not return to within 1" (25.4 mm) of unloaded height, see «VEHICLE WILL NOT LOWER»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control__vehicle-will-not-lower) under ELECTRICAL TESTING.
7. Remove 300 lbs. (136 kg) of weight from rear of vehicle. If system does not exhaust within 8-15 seconds, go to «VEHICLE WILL NOT LOWER»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control__vehicle-will-not-lower) under ELECTRICAL TESTING. If system exhausts within 8-15 seconds, but vehicle does not return to within 1.00" (25.4 mm) of unloaded height, see «HEIGHT SENSOR»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control) under ADJUSTMENTS.
8. If system exhausts within 8-15 seconds, and after 2 minutes the vehicle returns to within 1" (25.4 mm) of unloaded height, system is operating correctly.

SYSTEM LEAK TEST

Note. System leak test will determine if a leak exists and if leak is internal or external to compressor.

1. Install Pressure Gauge (J-22124-A ) and Air Hose Set (J-22124-91 ) to air drier and air adjustable shock absorbers. (Scheme 2) With shut-off valve open, apply shop air pressure through service valve on pressure gauge until pressure gauge reaches 100-120 psi (7.0-8.4 kg/cm 2 ).
2. If a leak is indicated, close shutoff valve. This isolates compressor from rest of system. Check for decrease in air pressure. If air pressure continues to decrease, leak is external to compressor.
3. If air pressure stops decreasing after shutoff valve is closed, leak is in compressor. See «COMPRESSOR LEAK TEST»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control__compressor-leak-test) under COMPONENT TESTING. If air pressure continues to decrease, leak is external to compressor. Test all connections using soapy water solution and repair as necessary.
4. If air pressure increases rapidly but vehicle does not rise, check for pinched air line and stuck or binding air adjustable shock absorbers.

Scheme 2

AIR DRIER TEST

Note. Air drier is tested to ensure valve maintains a minimum pressure of 8-14 psi (.56-.98 kg/cm 2 ) in air adjustable shock absorbers.

1. Install Pressure Gauge (J-22124-A ) to air drier and air adjustable shock absorbers using Air Hose Set (J-22124-91 ). (Scheme 2) Turn ignition on. Disconnect height sensor arm link from rear axle.
2. Move arm upward to inflate shock absorbers. Move arm downward to deflate shock absorbers. Note pressure gauge reading. Turn ignition off to deflate shock absorbers through pressure gauge valve. Pressure gauge should read 8-14 psi (.56-.98 kg/cm 2 ) after air adjustable shock absorbers are deflated. If air pressure reading is not within specification, replace air drier.

COMPRESSOR OPERATION TEST

Note. This test measures amount of compressor current draw, air output and pressure leak-down.

1. Remove compressor. See «COMPRESSOR»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control) under REMOVAL & INSTALLATION. Connect Pressure Gauge (J-22124-A ) to air drier. (Scheme 3)
2. Connect one ammeter lead to battery positive (B+) terminal and other lead to Green wire at compressor electrical connector. Ground Black wire terminal of compressor electrical connector. Note compressor motor current draw.
3. If compressor does not operate or current draw exceeds 14 amps, replace compressor. If current draw is 14 amps or less, allow pressure to reach 100 psi (7.0 kg/cm 2 ) and then disconnect ammeter from compressor connector.
4. If pressure holds at 100 psi (7.0 kg/cm 2 ), compressor is okay. If pressure decreases to less than 90 psi (6.3 kg/cm 2 ), but does not continue to decrease, replace compressor head assembly. See «COMPRESSOR HEAD ASSEMBLY»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control) under REMOVAL & INSTALLATION.
5. If pressure fully leaks off, or pressure builds up, but does not reach 100 psi (7.0 kg/cm 2 ), check compressor for leaks. See «COMPRESSOR LEAK TEST»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control__compressor-leak-test).

Scheme 3

COMPRESSOR LEAK TEST

1. Remove compressor. See «COMPRESSOR»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control) under REMOVAL & INSTALLATION. Connect Pressure Gauge (J-22124-A ) to air drier. (Scheme 3) Apply shop air pressure through service valve on pressure gauge until pressure is 100 psi (7.0 kg/cm 2 ).
2. Using soapy water solution, check for leaks around air drier cover, air drier "O" ring casting bore, edge of cover gasket, edge of solenoid valve housing and air intake and exhaust opening in head casting. (Scheme 4)
3. If leak exists at cover bolts, tighten cover bolts to specification and then check for leaks. See «TORQUE SPECIFICATIONS»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control) table at the end of this article. Remove pressure gauge.

Scheme 4

HEIGHT SENSOR TEST

1. Turn ignition off and then on to reset height sensor timing circuit. Raise and support vehicle. Using jack stands, raise rear axle until rear riding height is 10.4" (264 mm). To measure rear riding height, mark a spot on bottom of outer rocker panel, 24" (610 mm) forward of rear axle center line. (Scheme 5)
2. Measure distance between marked spot and ground line (ground line is horizontal line between bottom of front and rear tires). This distance is rear riding height. Disconnect link from height sensor metal arm. Ensure height sensor electrical connector is secure. Move and hold height sensor arm assembly upward for at least 15 seconds.
3. If compressor does not operate within 8-15 seconds, go to «COMPRESSOR INOPERATIVE»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control__compressor-inoperative) under ELECTRICAL TESTING. If compressor operates within 8-15 seconds, hold arm upward until air shock absorbers are filled, and then move arm downward until compressor stops.
4. Move height sensor downward past area where compressor stopped. If air adjustable shock absorbers start to deflate after 8-15 seconds, system is okay. If air adjustable shock absorbers do not start to deflate after 8-15 seconds, repair wiring or replace height sensor as necessary. Connect arm to link. Lower vehicle.

Scheme 5

COMPRESSOR INOPERATIVE

Note. For connector terminal identification, see WIRING DIAGRAM .

Preliminary Test

Disconnect height sensor connector. Connect a fused jumper wire between ground and terminal "B" (Yellow wire) of height sensor connector. If compressor operates, perform TEST NO. 1. If compressor does not operate, perform TEST NO. 2.

Test No. 1

1. Disconnect fused jumper wire. Connect test light between ground and terminal "C" (Orange wire) of height sensor connector. If test light does not come on, repair open in Orange wire between height sensor and circuit splice. If test light comes on, connect test light between terminals "C" and "A" (Orange and Black wires) of height sensor connector.
2. If test light does not come on, repair open in Black wire between height sensor and ground. If test light comes on, turn ignition switch to RUN position. Connect test light between ground and terminal "D" (Pink/Black wire) of height sensor connector.
3. If test light does not come on, repair open in Pink/Black wire between height sensor and fuse No. 17. If test light comes on, check for poor connection at height sensor connector. If connection is okay, adjust height sensor. See «HEIGHT SENSOR»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control) under ADJUSTMENTS. Retest system. If system still does not operate, replace height sensor.

Test No. 2

1. Disconnect compressor relay connector. Connect a fused jumper wire between terminals No. 1 and 4 of compressor relay connector (leave jumper wire connected only as long as necessary to check compressor operation). If compressor operates, go to step 5).
2. If compressor does not operate, connect a test light between ground and terminal No. 1 of compressor relay connector. If test light comes on, go to step 4).
3. If test light does not come on, check for poor connection at compressor connector and height sensor connector. If connections are okay, repair open in Orange wire between fuse No. 4 and compressor relay.
4. Check for poor connection or open in Yellow wire circuit between compressor relay and height sensor. If circuit is okay, replace compressor relay.
5. Connect a test light between ground and terminal No. 5 of compressor relay connector. If test light comes on, go to next step. If test light does not come on, check for poor connection at compressor connector. If connection is okay, repair open in Orange wire between compressor relay and circuit splice.
6. Disconnect compressor connector. Connect test light between terminal No. 1 of compressor relay and Black wire terminal of compressor connector.
7. If test light comes on, go to next step. If test light does not come on, check for poor connection at compressor connector. If connector is okay, repair open in Black wire circuit between compressor and ground.
8. Check for poor connection at compressor connector. If connection is okay, replace compressor assembly.

VEHICLE WILL NOT LOWER

Note. This procedure checks operation of exhaust solenoid valve in compressor head. If exhaust solenoid valve is defective, replace compressor head.

Disconnect height sensor connector. Connect a fused jumper wire between ground and terminal "E" (White wire) of height sensor connector. If exhaust solenoid valve does not click and air is not exhausted, perform TEST NO. 1. If exhaust solenoid valve clicks and air is exhausted, perform TEST NO. 2.

1. Connect test light between ground and terminal "C" (Orange wire) of compressor connector. If test light comes on, go to next step. If test light does not come on, check for poor connection at compressor connector. If connection is okay, repair open in Orange wire between compressor connector and circuit splice.
2. Check for poor connection or open in White wire between compressor and height sensor. If connection is okay, replace compressor head. See «COMPRESSOR HEAD ASSEMBLY»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control) under REMOVAL & INSTALLATION.

1. Connect test light between terminals "C" and "A" (Orange and Black wires) of height sensor connector. If test light comes on, go to next step. If test light does not come on, check for poor connection at height sensor connector. If connection is okay, repair open in Black wire circuit between height sensor and ground.
2. Check for poor connection at height sensor connector. If connection is okay, adjust height sensor. See «HEIGHT SENSOR»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control) under ADJUSTMENTS. Retest system. If system still does not operate, replace height sensor.

COMPRESSOR OPERATES CONTINUOUSLY (LONGER THAN 7 MINUTES)

Note. For connector terminal identification, see WIRING DIAGRAM .

1. Disconnect compressor relay connector. If compressor continues to operate, replace compressor. If compressor stops operating, connect test light between terminals No. 2 and 5 of compressor relay connector.
2. If test light does not come on, replace compressor relay. If test light comes on, disconnect height sensor connector. Connect test light between terminals "B" and "C" (Yellow and Orange wires) of height sensor connector. If test light comes on, repair short to ground in Yellow wire between compressor relay and height sensor. If test light does not come on, replace height sensor.

REMOVAL & INSTALLATION

Removal

Raise and support vehicle. Support rear axle. Disconnect air lines from shock absorbers by rotating spring clip and removing air line. Remove upper bolts and nuts on shock absorber. Remove lower nut and washer. DO Not allow lower stud to rotate when removing nut. Remove shock absorbers.

Installation

To install, reverse removal procedure. Tighten bolts and nuts to specification. See TORQUE SPECIFICATIONS table at the end of this article. Before installing air lines, lubricate "O" rings with petroleum jelly. Ensure air line and connector are fully seated in fitting.

1. Remove compressor and bracket. See «COMPRESSOR»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control) . Remove air drier-to-compressor bolts. Rotate retaining clip on air drier 90 degrees. Rotate air drier. Remove air drier and "O" ring.
2. To install, reverse removal procedure. Lubricate "O" ring with petroleum jelly before installing. Tighten bolts to specification. See «TORQUE SPECIFICATIONS»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control) table at the end of this article.

Disconnect hose from air filter. Remove retaining bolt and air filter. To install, reverse removal procedure. Tighten bolt to specification. See TORQUE SPECIFICATIONS table at the end of this article.

1. Disconnect negative battery cable. Raise and support vehicle. Disconnect air lines by rotating spring clip and removing air line. Remove compressor and bracket-to-crossmember bolts.
2. Disconnect anti-lock brake wheel speed sensor wiring from bracket. Disconnect electrical connection at compressor. Remove compressor and bracket from crossmember. Remove compressor-to-bracket bolts. Separate compressor from bracket.

To install, reverse removal procedure. Tighten bolts to specification. See TORQUE SPECIFICATIONS table at the end of this article. Before installing air lines, lubricate "O" rings with petroleum jelly. Ensure air line and connector are fully seated in fitting.

Remove air drier. See AIR DRIER . Remove 3 compressor head-to-compressor retaining bolts. Remove compressor head and "O" ring. To install, reverse removal procedure using new "O" ring. Tighten bolts to specification, starting with center bolt. See TORQUE SPECIFICATIONS table at the end of this article.

Note. Compressor relay may be serviced without removing compressor from bracket.

1. Remove compressor and bracket. See «COMPRESSOR»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control) . Remove compressor relay retaining bolt. Disconnect electrical connector and remove compressor relay.
2. To install, reverse removal procedure. Tighten bolts to specification. See «TORQUE SPECIFICATIONS»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control) table at the end of this article.

Exhaust solenoid valve is not serviceable. Replace compressor head if exhaust solenoid valve is defective. See COMPRESSOR HEAD ASSEMBLY .

1. Disconnect negative battery cable. Raise and support vehicle. Disconnect height sensor connector. Remove link-to-upper control arm nut. Remove retaining bolts and height sensor.
2. To install, reverse removal procedure. Tighten bolts and nuts to specification. See «TORQUE SPECIFICATIONS»(/buick/roadmaster/viii-1991-1996/remont/electronic-suspension/#suspension-rear-electronic-level-control) table at the end of this article.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

Electronic Level Control System Wiring Diagram. Scheme 6

See also:
• AIR DRIER TEST
• HEIGHT SENSOR
• COMPRESSOR INOPERATIVE
• HEIGHT SENSOR TEST
• COMPRESSOR LEAK TEST
• VEHICLE WILL NOT LOWER