Rear Automatic Suspension problem

[tobbyjl]

Hi

I just notice when I start my car the rear suspension-compressor doesn't activate. I already check the fuse and relays and they are fine. I proceed to disconnect the battery, wait 15mins and connect again. Then I start the car and the compressor activate, but then after I turn the car off and on again doesn't activate.

HELP!!! What can It be?

[bobgto65]

If you mean that it is supposed to turn on every time you turn on the ignition, that is not correct. It will only turn on if the car needs leveling. You can test it with the engine running by turning on the inflation switch in the trunk.

[1tinindian]

You may find this description helpful.

Leon




Automatic Level Control Description and Operation
Automatic Level Control (ALC)
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 rear integration control module (RIM), height sensor, an air compressor assembly, an ALC compressor relay, an intake hose and filter, an air tube, two rear shock absorber, and an accessory inflator switch. 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 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. The accessory inflator is activated by a switch in the rear compartment.

Raising the Vehicle
When a load is added to the vehicle, the vehicle body moves down causing the sensor actuating arm to rotate upward. (An arm movement of about 25 mm (1 in) amounts to a height change of about 12 mm (1/2 in) at the rear bumper.) The upward arm movement activates an internal timing circuit of the RIM module and, after an initial fixed delay of 17 to 27 seconds, the RIM module provides a ground to complete the compressor relay circuit. The 12V (+) circuit to the compressor is then complete and the compressor runs, sending pressurized air to the struts through the air tubes.

As the struts inflate, the vehicle body moves upward rotating the actuating arm towards its original position. Once the body reaches its original height, +/− 25 mm (+/− 1 in), the RIM module opens the compressor relay circuit, and the compressor is turned off.

Air Compressor Head Relief Sequence
In order to reduce current draw during air compressor starting, the RIM 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:

•Exhaust solenoid is energized.
•Air compressor is activated 1.3 seconds after the exhaust solenoid is energized.
•Exhaust solenoid is de-energized 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 of the RIM module. After the initial fixed delay, the RIM module provides a ground to complete the exhaust solenoid circuit, energizing the solenoid. Now, air starts exhausting out of the struts, 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 original height, +/− 25 mm (+/− 1 in), the RIM module opens the exhaust solenoid circuit, which closes the exhaust solenoid and prevents air from escaping.

Air Replenishment Cycle
The sensor actuating arm position is checked when the ignition is turned on. If the sensor indicates that no height adjustment is needed, an internal timer circuit of the RIM module is activated. After about 35 to 55 seconds, the compressor is turned on for 3 to 5 seconds. This ensures that the struts are filled with the proper residual pressure. If weight is added to or removed from the vehicle during the time delay, the air replenishment cycle is overridden, and the vehicle rises or lowers after the normal delay.

Accessory Inflator
The manually operated switch is located in the rear compartment and is powered and monitored by the RIM. When the momentary switch is closed, with the key in the ON position, the RIM commands the ALC relay On, which engages the low volume, high pressure ALC compressor for approximately 10 minutes to allow inflation of off — vehicle accessories. The accessory inflation cycle may be stopped at any time during the cycle either by pressing the inflator switch again or changing the ignition cycle during operation of the compressor. After the original 10 minute cycle expires, the accessory inflator may be restarted again for another 10 minute cycle or until the accessory being inflated is complete.

Air Compressor Description
The air compressor is a positive displacement air pump, powered by a 12V 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 energized. 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:

•It contains desiccant 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.
•It contains valving that maintains a system residual pressure of 48–97 kPa (7–14 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:

•When energized, it exhausts air from the rear struts.
•It acts as a relief valve to limit the maximum air pressure output of the compressor.
Air Inflator System
The air inflator system is included as part of the ALC system. The function of the inflator system is to provide air under pressure to inflate items other than the ALC system shocks, such as bike tires, sport balls, automobile tires, etc. The inflator fill valve and switch are located in the rear compartment and will ONLY operate with the ignition in the ON position.

Automatic Level Control Sensor Description
The suspension position sensor is a potentiometer which detects height changes at the rear of the vehicle and, in turn, relays these changes to the RIM, which controls the functions of the compressor and exhaust solenoid. To prevent energizing the compressor relay or exhaust solenoid during normal ride motions, the RIM provides a calibrated delay before ground is completed to either circuit.

The sensor is mounted to the left rear side of the rear suspension support assembly. The actuation arm is attached to the left rear control arm by a short link.

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:

•One connector at the ALC air dryer
•Two tubes between the ALC air dryer and the two rear shock absorbers
•Two connectors with spring clips one 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.

[CMNTMXR57]

I read this yesterday and never got around to responding...

It sounds like NOTHING is wrong with the system. It IS doing it's job. It ISN'T meant to level it each and every time the car is started. Only when it needs it. Which means if it isn't doing it every time, the air components are holding pressure and maintaining the vehicle at a level plane.

[00Beast]

Quick test: Turn the car on, pop the trunk and push the AIR button by the trunk latch. Does the compressor activate? And/or sit in the trunk and see if it kicks on to level itself. IIRC, the compressor usually cycles on a few seconds after you start the car as a self-check, but I don't know if that's always the case...

[CMNTMXR57]

Right from GM above;

Air Replenishment Cycle
The sensor actuating arm position is checked when the ignition is turned on. If the sensor indicates that no height adjustment is needed, an internal timer circuit of the RIM module is activated. After about 35 to 55 seconds, the compressor is turned on for 3 to 5 seconds. This ensures that the struts are filled with the proper residual pressure. If weight is added to or removed from the vehicle during the time delay, the air replenishment cycle is overridden, and the vehicle rises or lowers after the normal delay.

[tobbyjl]

I try several things like sit on my trunk, press the AIR switch, check the relay and doesn't activate

Someone know if there's a way to 'reset' the system or something?

Any ideas?

[tobbyjl]

Any suggestions?

[CMNTMXR57]

Is the key in the "on" position?

[J Wikoff]

Check the labels on the fuse panels and locate the fuse for rhe ELC or Load Leveling. If it/they are fine, swap the relay with one from another circuit just to see if it works then.

[tobbyjl]

Yes, it only activates one when I disconnect and re-connect the battery. After that doesnt activate again. I'll try loading weight, sitting on the trunk and nothing came up. Looks like the computer is deactivating the system for some reason.

In addition to the relay, theres something else that i need to check?... the big question is.. starts to work and then dont. So it can be a fuse or relay...

[Kadeas]

I don't have the aux air in the trunk. Was this an option? I do have the self-leveling rear suspension system though.