Suspension - Electronic Level Control Chevrolet Caprice Impala SS

DESCRIPTION

Electronic Level Control (ELC) automatically adjusts rear height of vehicle to compensate for vehicle load. System consists of compressor, air drier, exhaust solenoid valve, compressor relay, height sensor, air adjustable shock absorbers and connecting air lines. Air drier (mounted on compressor) contains moisture-absorbing dry chemical and valves that maintain minimum system air pressure at about 8-14 psi (.56-.98 kg/cm 2 ).

SYSTEM OPERATION

When weight is added to vehicle, height sensor arm rotates upward. When arm rotates upward, a time delay of about 8-15 seconds begins in the height sensor. After this delay, the height sensor grounds the compressor relay, allowing power to air compressor. Air is pumped into shock absorbers and vehicle rises. As vehicle rises, height sensor arm rotates downward until it reaches curb height position. Height sensor then opens ground circuit to compressor relay, turning compressor off.

When weight is removed from vehicle, height sensor arm rotates downward. After delay of about 8-15 seconds, downward rotation of arm grounds exhaust solenoid valve circuit, energizing exhaust solenoid valve. This causes air to vent from shock absorbers, lowering vehicle. As vehicle is lowered, height sensor arm rotates upward to curb height position. Height sensor opens exhaust solenoid valve circuit, causing exhaust solenoid valve to close.

To ensure system is operating with at least minimum air pressure, height sensor commands air replenishment cycle each time ignition is turned on. If height sensor determines that vehicle is at normal operating height, internal timer circuit is activated. After delay of about 35-40 seconds, compressor turns on for about 4 seconds to ensure residual system pressure exists. Air drier maintains minimum shock absorber air pressure of 8-14 psi (.56-.98 kg/cm 2 ).

If weight is added to or removed from vehicle during 35-40 second delay, air replenishment cycle will be overridden and vehicle will rise or lower after normal time delay.

Battery voltage is applied to compressor and height sensor at all times. This allows system to vent after load is removed with ignition off. Height sensor limits compressor operation or exhaust solenoid valve energized time to 4.5-7.0 minutes. Time limit is necessary to prevent continuous compressor operation in case of air leak. Turning ignition switch from OFF to ON position will reset compressor operation or exhaust solenoid valve energized time.

Low compressor motor starting current is obtained by 1.5 second actuation of exhaust solenoid valve. This reduces air pressure in compressor cylinder, allowing for easier compressor operation.

Air Adjustable Shock Absorber

Air adjustable shock absorber is a conventional shock absorber that contains an air chamber. When pressure is applied to air chamber, air chamber extends the shock absorber.

Air Drier

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

Compressor

Piston-type compressor is mounted on frame rail near left front wheelwell. Compressor provides air pressure for system.

Compressor Relay

Height sensor grounds the compressor relay, allowing power to compressor. Compressor relay is mounted on compressor.

Exhaust Solenoid Valve

Exhaust solenoid valve (part of compressor head assembly) is controlled by height sensor. Valve exhausts air from system and limits compressor output pressure by acting as a blow-off valve.

Height Sensor

Height sensor is located on crossmember above rear axle. Movement of height sensor arm (attached to rear axle by a link) controls compressor relay and exhaust solenoid valve ground circuits to adjust vehicle height. Height sensor limits compressor operation or exhaust solenoid valve energized time to 4.5-7.0 minutes. Time limit is necessary to prevent continuous operation of compressor in case of air leak.

1. Adjust height sensor if riding height is not as specified. See appropriate RIDING HEIGHT ADJUSTMENT article in WHEEL ALIGNMENT section: «RIDING HEIGHT ADJUSTMENT»(/chevrolet/caprice-impala-ss/1995-1996/remont/wheel-alignment/#riding-height-adjustment) - Caprice, Impala SS, Roadmaster «RIDING HEIGHT ADJUSTMENT»(ref-52982) - Fleetwood
2. Vehicle should be on level surface with full gas tank and no load in vehicle. Push bumper down and up slowly a few times to normalize suspension. Turn ignition on.
3. Loosen lock bolt securing height sensor metal arm to plastic arm bracket. (Scheme 1) To increase riding height, move metal arm upward in relation to plastic arm bracket. To decrease riding height, move metal arm downward in relation to plastic arm bracket. Tighten lock nut. Allow for delay when rechecking riding height. If adjustment cannot be made, repair problem with rear springs or suspension.

Note. Height sensor arm angle can be changed a total of 5 degrees. One degree of change in arm angle results in about 1/4" (6 mm) change in riding height. Total change in riding height is about 1 1/4" (32 mm).

Scheme 1

RIDING HEIGHT

Note. See appropriate RIDING HEIGHT ADJUSTMENT article in WHEEL ALIGNMENT section: RIDING HEIGHT ADJUSTMENT - Caprice, Impala SS, Roadmaster RIDING HEIGHT ADJUSTMENT - Fleetwood

SYSTEM OPERATION TEST

1. Place vehicle on flat surface. Remove heavy items from vehicle. Measure distance between floor and a suitable spot on rocker panel, 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 one inch (25.4 mm) of unloaded height measured in step 1), go to «AIR DRIER TEST»(/chevrolet/caprice-impala-ss/1995-1996/remont/electronic-suspension/#suspension-electronic-level-control__air-drier-test) under COMPONENT TESTING.
3. If compressor does not start within 8-15 seconds, and vehicle is not within one inch (25.4 mm) of unloaded height, adjust height sensor, and then retest system. See «HEIGHT SENSOR»(/chevrolet/caprice-impala-ss/1995-1996/remont/electronic-suspension/#suspension-electronic-level-control) under ADJUSTMENTS. If compressor still does not start within 8-15 seconds, go to «COMPRESSOR INOPERATIVE»(/chevrolet/caprice-impala-ss/1995-1996/remont/electronic-suspension/#suspension-electronic-level-control__compressor-inoperative) under ELECTRICAL TESTING.
4. If compressor stops within 7 minutes, go to next step. If compressor runs continuously, go to «HEIGHT SENSOR TEST»(/chevrolet/caprice-impala-ss/1995-1996/remont/electronic-suspension/#suspension-electronic-level-control__height-sensor-test) under COMPONENT TESTING.
5. If system leaks down, go to «COMPRESSOR LEAK TEST»(/chevrolet/caprice-impala-ss/1995-1996/remont/electronic-suspension/#suspension-electronic-level-control__compressor-leak-test) under COMPONENT TESTING. If vehicle returns to within one inch (25.4 mm) of unloaded height, go to step 7).
6. If vehicle does not return to within one inch (25.4 mm) of unloaded height, adjust height sensor, and retest system. See «HEIGHT SENSOR»(/chevrolet/caprice-impala-ss/1995-1996/remont/electronic-suspension/#suspension-electronic-level-control) under ADJUSTMENTS. If vehicle still does not return to within one inch (25.4 mm) of unloaded height, go to «VEHICLE WILL NOT LOWER»(/chevrolet/caprice-impala-ss/1995-1996/remont/electronic-suspension/#suspension-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»(/chevrolet/caprice-impala-ss/1995-1996/remont/electronic-suspension/#suspension-electronic-level-control__vehicle-will-not-lower) under ELECTRICAL TESTING. If system exhausts within 8-15 seconds, but vehicle does not return to within one inch (25.4 mm) of unloaded height, adjust height sensor. See «HEIGHT SENSOR»(/chevrolet/caprice-impala-ss/1995-1996/remont/electronic-suspension/#suspension-electronic-level-control) under ADJUSTMENTS.
8. If system exhausts within 8-15 seconds, and after 2 minutes the vehicle returns to within one inch (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 Adapter Hose (J-22124-91 ) in line between air drier fitting at compressor and existing air line to shock absorbers. (Scheme 2) Install pressure gauge so shutoff valve is on compressor side of gauge. With shutoff valve open, apply shop air pressure through service valve until gauge reads 100-120 psi (7.03-8.43 kg/cm 2 ).
2. If leak is indicated, close shutoff valve to isolate compressor and continue to watch gauge for decrease in pressure. If pressure continues to decrease, leak is external to compressor. Leak test all connections.
3. If pressure stops decreasing after shutoff valve is closed, leak is in compressor assembly. Check compressor for leaks. See «COMPRESSOR LEAK TEST»(/chevrolet/caprice-impala-ss/1995-1996/remont/electronic-suspension/#suspension-electronic-level-control__compressor-leak-test) under COMPONENT TESTING. If pressure builds up rapidly but vehicle does not rise, check for pinched air line and stuck or binding shocks.

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 ) and Adapter Hose (J-22124-91 ). (Scheme 2) Turn ignition on. Disconnect link from height sensor metal arm.
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. Connect Adapter Hose (J-22124-91 ) to air drier fitting. Connect Pressure Gauge (J-22124-A ) to adapter hose.
2. Connect 12-volt power supply and ammeter to compressor harness terminals to measure current draw. (Scheme 3) If current draw exceeds 14 amps or compressor motor does not run, replace compressor.
3. 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. If pressure holds at 100 psi (7.0 kg/cm 2 ), compressor is okay.
4. 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»(/chevrolet/caprice-impala-ss/1995-1996/remont/electronic-suspension/#suspension-electronic-level-control) under REMOVAL & INSTALLATION. If pressure fully leaks off, or pressure builds up but does not reach 100 psi (7.0kg/cm 2 ), check compressor for leaks. See «COMPRESSOR LEAK TEST»(/chevrolet/caprice-impala-ss/1995-1996/remont/electronic-suspension/#suspension-electronic-level-control__compressor-leak-test).

Scheme 3

COMPRESSOR LEAK TEST

1. Remove compressor. Connect Adapter Hose (J-22124-91 ) to air drier fitting. Connect Pressure Gauge (J-22124-A ) to adapter hose. 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 compressor head bolts, tighten bolts to specification, and recheck for leaks. See «TORQUE SPECIFICATIONS»(/chevrolet/caprice-impala-ss/1995-1996/remont/electronic-suspension/#suspension-electronic-level-control) table. Remove pressure gauge.

Scheme 4

HEIGHT SENSOR TEST

1. Turn ignition off then on to reset height sensor timer circuit. Raise vehicle on hoist by wheels (alignment rack type hoist) or by rear axle to position vehicle at normal riding height.
2. Disconnect link from height sensor metal arm. Ensure height sensor connector is securely connected and ground wire is secure. Move height sensor metal and plastic arm assemblies upward. After 8-15 second delay, compressor should turn on and inflate shocks. If compressor does not turn on, go to «COMPRESSOR INOPERATIVE»(/chevrolet/caprice-impala-ss/1995-1996/remont/electronic-suspension/#suspension-electronic-level-control__compressor-inoperative) under ELECTRICAL TESTING. If compressor turns on and shocks start to inflate, move metal and plastic arm assemblies down until compressor just stops.
3. Move metal and plastic arm assemblies down to point just below where compressor stopped. After 8-15 second delay, shocks should begin to deflate. If shocks do not begin to deflate, go to «VEHICLE WILL NOT LOWER»(/chevrolet/caprice-impala-ss/1995-1996/remont/electronic-suspension/#suspension-electronic-level-control__vehicle-will-not-lower) under ELECTRICAL TESTING. Reconnect link to height sensor metal arm. Lower vehicle.

ELECTRICAL TESTING

Note. Use SYSTEM OPERATION TEST under SYSTEM TESTING as a guide to determine which test to perform. Before performing test, ensure system fuses are okay and link is connected between height sensor and suspension control arm. When using the following procedures, refer to appropriate wiring diagram. See WIRING DIAGRAMS .

COMPRESSOR INOPERATIVE

Note. For connector terminal identification, see WIRING DIAGRAMS .

Preliminary Test

Disconnect height sensor connector. Connect a fused jumper wire between ground and Yellow wire (terminal "B") 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 Orange wire (terminal "C") of height sensor connector. If test light does not come on, repair open Orange wire. If test light comes on, connect test light between Orange wire and Black wire terminals (terminals "C" and "A") of height sensor connector.
2. If test light does not come on, repair open Black wire. If test light comes on, turn ignition switch to RUN position. Connect test light between ground and Pink/Black wire terminal (terminal "D") of height sensor connector.
3. If test light does not come on, repair open Pink/Black wire. If test light comes on, check for poor connection at height sensor connector. If connection is okay, adjust height sensor. See «HEIGHT SENSOR»(/chevrolet/caprice-impala-ss/1995-1996/remont/electronic-suspension/#suspension-electronic-level-control) under ADJUSTMENTS. Retest system. If system still does not operate, replace height sensor.

Test No. 2

Disconnect compressor relay connector. Connect a fused jumper wire between Orange and Black wire terminals of compressor relay connector (leave jumper wire connected only as long as necessary to check compressor operation). If compressor operates, go to TEST NO. 3. If compressor does not operate, go to TEST NO. 4.

Test No. 3

Connect a test light between ground and Orange wire terminal of compressor relay connector (terminal No. 5 on Caprice, Impala SS and Roadmaster; terminal No. 2 on Fleetwood). If test light does not come on, repair open Orange wire. If test light comes on, check for open Yellow wire between compressor relay and height sensor. If Yellow wire is okay, replace compressor relay.

Test No. 4

Connect a test light between ground and Orange wire terminal of compressor relay connector (terminal No. 1 on Caprice, Impala SS and Roadmaster; terminal No. 3 on Fleetwood). If test light does not come on, repair open Orange wire. If test light comes on, check for open Black wire between compressor and ground. If Black wire 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. For connector terminal identification, see WIRING DIAGRAMS .

Disconnect height sensor connector. Connect a fused jumper wire between ground and White wire terminal (terminal "E") 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.

Disconnect compressor connector. Connect test light between ground and Orange wire terminal (terminal"C") of compressor connector. If test light does not come on, check for open Orange wire. If test light comes on, check for open White wire between compressor and height sensor. If White wire is okay, replace compressor head assembly. See COMPRESSOR HEAD under REMOVAL & INSTALLATION.

Connect test light between Orange and Black wire terminals (terminals "C" and "A") of height sensor connector. If test light does not come on, repair open Black wire. If test light comes on, check for poor connection at height sensor connector. If connection is okay, adjust height sensor. See HEIGHT SENSOR 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 DIAGRAMS .

1. Disconnect compressor relay connector. If compressor continues to operate, repair short to battery voltage in appropriate wire. If compressor stops operating, connect test light between Orange and Yellow wire terminals of compressor relay connector (terminals No. 5 and 2 on Caprice, Impala SS and Roadmaster; terminals No. 2 and 1 on Fleetwood).
2. If test light does not come on, replace compressor relay. If test light comes on, disconnect height sensor connector. Connect test light between Yellow and Orange wire terminals (terminals "B" and "C") of height sensor connector.
3. 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. Before installing air lines, lubricate "O" rings with petroleum jelly. Ensure air line and connector are fully seated in fitting.

Disconnect negative battery cable. Raise and support vehicle. Disconnect height sensor harness. Disconnect height sensor link from height sensor actuating arm. Remove height sensor screws.

To install, reverse removal procedure. Tighten height sensor screws to specification. See TORQUE SPECIFICATIONS table. Adjust height sensor. See HEIGHT SENSOR under ADJUSTMENTS.

Disconnect negative battery cable. Raise and support vehicle. Remove cover from left front wheelwell for access to compressor on frame rail. Disconnect compressor electrical connectors. Disconnect air lines as necessary. Remove compressor bolts and compressor.

To install, reverse removal procedure. Pre-pressurize system by grounding test connector (Yellow wire terminal) with jumper wire. Turn ignition on and allow system to cycle. Check for leaks using soap and water solution.

Remove air drier. See AIR DRIER . Remove head-to-compressor screws. Remove head and "O" ring seal.

To install, reverse removal procedure. Use NEW "O" ring seal. Pre-pressurize system by grounding test connector (Yellow wire terminal) with jumper wire. Turn ignition on and allow system to cycle. Check for leaks using soap and water solution.

Disconnect high pressure line by turning spring clip 90 degrees and removing tube assembly. Disconnect drier from compressor by turning spring clip and sliding drier and "O" ring from compressor head assembly.

Lubricate "O" ring and install in port of compressor head. Return retainer spring to its original position. Install drier on compressor head assembly. If difficulty arises when installing drier in compressor head assembly, rotate slightly while applying pressure. Check system for leaks.

AIR LINE REPAIR

Repair air line by splicing coupling at leak area. Inflate system to 100 psi (7.0 kg/cm 2 ). Use soap and water solution to locate leak. Deflate system through service valve, and cut out leaking area. Install coupling, and tighten tube nuts to 72 INCH lbs. (8 N.m). (Scheme 5) Inflate system, and check for leaks using soap and water solution.

Scheme 5

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

ELC System Wiring Diagram (Caprice, Impala SS & Roadmaster). Scheme 6

ELC System Wiring Diagram (Fleetwood). Scheme 7

See also:
• RIDING HEIGHT ADJUSTMENT
• COMPUTER RELEARN PROCEDURES
• AIR DRIER TEST
• HEIGHT SENSOR
• COMPRESSOR INOPERATIVE
• HEIGHT SENSOR TEST
• COMPRESSOR LEAK TEST
• VEHICLE WILL NOT LOWER
• SYSTEM OPERATION TEST