It is normal for some cycling of the compressor as the ride heights change and the compressor vents and fills air springs. Info:
The air compressor:
- Is not interchangeable with the rear air suspension (RAS) air compressor.
- Consists of the compressor and vent solenoid; neither are replaceable as individual items.
- Is a single cylinder electric motor driven unit that provides pressurized air as required.
- Is powered by a solid state relay, which is controlled by the air suspension control module.
- Passes pressurized air through the compressor air drier that contains silica gel (a drying agent). Moisture is then removed from the compressor air drier when vented air passes out of the system during vent operation.
- The drier may be replaced separately.
- The drier has dual ports and is not interchangeable with the RAS drier.
The vent solenoid:
- Allows air to escape from the system during venting actions.
- Is part of the air compressor cylinder head.
- Shares a common electrical connector with the air compressor motor.
- Is enclosed in the cylinder head casting, which forms an integral valve housing that allows the valve tip to enter the pressurized side of the system.
- Has an O-ring seal that prevents air leakage past the valve tip.
- Opens when the air suspension control module determines lowering is required.
- Provides an escape route for pressurized air when system pressures exceed safe operating levels.
- Has a 1792 kPa (260 psi) internal relief valve.
- Is installed with the air compressor as a unit.
A solid state relay is used in the air suspension system for compressor control. The relay incorporates a custom power metal oxide semi-conductor field effect transistor (MOSFET) and ceramic hybrid circuitry. The relay switches high current loads in response to low power signals and is controlled by the logic of the air suspension control module.
The compressor solid state relay is energized by the air suspension control module to have high current flow from the battery to the compressor motor.
The 4WAS control module is also used for the RAS system. The internal processor recognizes external circuitry to determine if it is installed in a 4WAS or a RAS system.
The air suspension control module is calibrated with information from the air suspension height sensors. A new or swapped air suspension control module requires the ride height adjustment calibration process to be performed.
A microcontroller-based electronic air suspension control module controls the air compressor motor (through a solid state relay) and all system solenoids. The air suspension control module also provides power to front and rear height sensors. The air suspension control module controls vehicle height adjustments by monitoring the two height sensors, vehicle speed, a steering sensor, acceleration input, the door ajar signal, transfer case signals and the brake pedal position (BPP) switch. The air suspension control module also conducts all fail-safe and diagnostic strategies and contains self-test and communication software for testing the vehicle and related components.
The air suspension control module is interchangeable between the RAS and 4WAS system.
The air suspension control module monitors and controls the system through a 32-pin two-way connector. The air suspension control module is keyed so that it cannot be plugged into an incorrect harness. There are two sides of the harness connection to the air suspension control module. Each is uniquely colored and keyed to prevent reversing the connections.
Pressure Relief Valve
The pressure relief valve (PRV) protects the rear air suspension components by venting the system to a specific pressure in the case of a system malfunction. The system will decrease the pressure to an acceptable level to maintain vehicle height. In the normal operation mode with normal system pressure, the PRV is constantly closed and does not have any effect on the system performance or function. The PRV is replaceable without any air lines.
- If the concern remains after the inspection, use New Generation STAR (NGS) Tester connected to the data link connector (DLC) to retrieve continuous diagnostic trouble codes (DTCs) and to execute On-Demand Self-Test diagnostics for the air suspension control module.
- If the On-Demand Self-Test is passed and no DTCs are retrieved, go to the Symptom Chart to continue diagnostics.
- If DTCs are retrieved, go to Air Suspension Control Module Diagnostic Trouble Code (DTC) Index in this section.
- If the air suspension control module cannot be accessed by NGS Tester, go to Pinpoint Test A.
Verify that the following conditions are met before running the On-Demand Self-Test.
- All doors, liftgate, and liftgate glass must be closed.
- The transmission is in PARK.
- The BPP switch is not pressed during the test and the parking brake is not set.
- The accelerator pedal is not pressed during the test.
- The vehicle is not in 4L mode.
- Fulfill the pre-conditions.
- Install a battery charger for the On-Demand Self-Test to prevent battery drain.
- Run the air suspension On-Demand Self-Test.
- Record all listed DTCs.
- Retrieve stored DTCs.
- Troubleshoot any On-Demand Self-Test DTCs first.
- Retest and clear DTCs after repairs.