Intermittent
Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to TESTING FOR ELECTRICAL INTERMITTENTS in Wiring Systems.
Rear Air Springs Do Not Inflate
| Step | Action | Yes | No |
|---|---|---|---|
| Schematic Reference: Suspension Controls Schematics | |||
| 1 | Did you perform the Air Suspension Diagnostic System Check? | Go to Step 2 | Go to Diagnostic System Check - Air Suspension |
| 2 | Verify the fault is present. Does the system operate normally? | Go to TESTING FOR INTERMITTENT CONDITIONS AND POOR CONNECTIONS in Wiring Systems | Go to Step 3 |
| 3 | Turn OFF the ignition. Disconnect the Air Suspension Compressor Assembly. Turn ON the ignition, with the engine OFF. Connect a test lamp between the ground circuit of the Air Suspension Compressor Assembly and a battery positive voltage circuit. Does the test lamp illuminate? | Go to Step 4 | Go to Step 7 |
| 4 | Test the battery positive voltage circuit of the Air Suspension Compressor Assembly for an open, short to ground and high resistance. Refer to CIRCUIT TESTING , TESTING FOR SHORT TO GROUND or TESTING FOR INTERMITTENT CONDITIONS AND POOR CONNECTIONS in Wiring Systems. Did you find and correct the condition? | Go to Step 9 | Go to Step 5 |
| 5 | Test the ignition 3 voltage circuit of the Air Suspension Compressor Assembly for an open, short to ground and high resistance. Refer to CIRCUIT TESTING , TESTING FOR SHORT TO GROUND or TESTING FOR INTERMITTENT CONDITIONS AND POOR CONNECTIONS in Wiring Systems. Did you find and correct the condition? | Go to Step 9 | Go to Step 6 |
| 6 | Inspect for poor connections at the harness connector of the Air Suspension Compressor Assembly. Did you find and correct the condition? | Go to Step 9 | Go to Step 8 |
| 7 | Repair the open in the Air Suspension Compressor Assembly ground circuit. Did you complete the repair? | Go to Step 9 | |
| 8 | Replace the Air Suspension Compressor Assembly. Refer to Air Spring Compressor Replacement . Did you complete the replacement? | Go to Step 9 | |
| 9 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 3 |
Rear Air Springs Do Not Inflate
Rear Air Springs Do Not Deflate
| Step | Action | Yes | No |
|---|---|---|---|
| Schematic Reference: Suspension Controls Schematics | |||
| 1 | Did you review the Air Suspension operation and perform the necessary inspections? | Go to Step 2 | Go to Air Suspension Description and Operation |
| 2 | IMPORTANT: The vehicle must be on a drive on hoist. Raise and support the vehicle. Disconnect the Air Suspension Compressor Assembly. Connect a test lamp between the battery positive voltage circuit of the Air Suspension Compressor Assembly harness and ground. Does the test lamp illuminate? | Go to Step 3 | Go to Step 6 |
| 3 | Connect a test lamp between the ground circuit of the Air Suspension Compressor Assembly harness and a battery positive voltage circuit. Does the test lamp illuminate? | Go to Step 4 | Go to Step 7 |
| 4 | Disconnect both air spring supply tubes at the Air Suspension Compressor Assembly. Did the vehicle lower? | Go to Step 5 | Go to Step 8 |
| 5 | Replace the Air Suspension Compressor Assembly. Refer to Air Spring Compressor Replacement . Did you complete the replacement? | Go to Step 10 | |
| 6 | Repair open circuit on the Air Suspension Compressor Assembly battery positive circuit. Did you complete the repair? | Go to Step 10 | |
| 7 | Repair open circuit on the Air Suspension Compressor Assembly ground circuit. Did you complete the repair? | Go to Step 10 | |
| 8 | Carefully inspect air tube assemble for damage. Was any damage found? | Go to Step 9 | |
| 9 | Repair or replace any damaged components. Is the repair complete? | Go to Step 10 | |
| 10 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Diagnostic System Check - Air Suspension |
| IMPORTANT |
|---|
| The vehicle must be on a drive on hoist. |
Rear Air Springs Do Not Deflate
Inflator Inoperative
| Step | Action | Yes | No |
|---|---|---|---|
| Schematic Reference: Suspension Controls Schematics | |||
| 1 | Did you perform the Air Suspension Diagnostic System Check? | Go to Step 2 | Go to Diagnostic System Check - Air Suspension |
| 2 | Verify the fault is present. Does the system operate normally? | Go to TESTING FOR INTERMITTENT CONDITIONS AND POOR CONNECTIONS in Wiring Systems | Go to Step 3 |
| 3 | Turn OFF the ignition. Disconnect the air suspension inflator switch at air suspension compressor assembly. Turn ON the ignition, with the engine OFF. Connect a test lamp between the inflater switch ground circuit of the air suspension compressor assembly and a battery positive voltage circuit. Does the test lamp illuminate? | Go to Step 4 | Go to Step 6 |
| 4 | Connect a 3 amp fused jumper wire between the control circuit of the air suspension compressor assembly and the ground circuit of the air suspension compressor assembly. Does the compressor start and run? | Go to Step 7 | Go to Step 5 |
| 5 | Test the control circuit of the air suspension inflator switch for an open, short to ground, short to voltage and high resistance. Refer to CIRCUIT TESTING , TESTING FOR SHORT TO GROUND or TESTING FOR INTERMITTENT CONDITIONS AND POOR CONNECTIONS in Wiring Systems. Did you find and correct the condition? | Go to Step 11 | Go to Step 8 |
| 6 | Inspect for poor connections at the harness connector of the Air Suspension Compressor Assembly. Did you find and correct the condition? | Go to Step 11 | Go to Step 9 |
| 7 | Inspect for poor connections at the harness connector of the air suspension inflator switch. Did you find and correct the condition? | Go to Step 11 | Go to Step 10 |
| 8 | Inspect for poor connections at the harness connector of the Air Suspension Compressor Assembly. Did you find and correct the condition? | Go to Step 11 | Go to Step 9 |
| 9 | Replace the Air Suspension Compressor Assembly. Refer to Air Spring Compressor Replacement . Did you complete the replacement? | Go to Step 11 | |
| 10 | Replace the air suspension inflator switch. Refer to Inflator Air Switch Replacement . Did you complete the replacement? | Go to Step 11 | |
| 11 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 3 |
Inflator Inoperative
Trim Height Uneven
| Step | Action | Yes | No |
|---|---|---|---|
| Schematic Reference: Suspension Controls Schematics | |||
| 1 | Did you perform the Air Suspension Diagnostic System Check? | Go to Step 2 | Go to Diagnostic System Check - Air Suspension |
| 2 | Verify the fault is present. Does the system operate normally? | Go to Air Spring Sensor Calibration Test for intermits and poor connection. | Go to Step 3 |
| 3 | Turn ignition ON with engine OFF. Does rear of vehicle raise to trim height and is level from side to side when viewing vehicle from rear? | Go to Step 4 | Go to Air Spring Sensor Calibration |
| 4 | Check Air Suspension System for small leaks. Did you find and correct the condition? | Go to Step 5 | |
| 5 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 3 |
Trim Height Uneven
Air Suspension
The primary mission of the Air Suspension System is the following for the rear suspension under loaded and unloaded conditions
- Keep the vehicle visually level
- Provide optimal headlight aiming
- Maintain optimal ride height
The Air Suspension System consists of the following items
- Air Suspension Compressor Assembly
- Air Suspension Sensors
- Rear Air Springs
The Air Suspension Compressor Assembly has the ability to detect faults and indicate the appropriate fault code via a blink code on the inflator switch LED. The Air Suspension Compressor Assembly will indicate the code when the condition to cause the code becomes current.
During compressor activation the exhaust valve will be activated for a calibrated length of time to provide compressor head relief. After a calibrated length of time the compressor relay will activate to start the compressor. When trim height is achieved the relay will be deactivated. The exhaust valve and compressor relay are part of the air suspension compressor assembly. The Air Suspension System shall maintain the rear trim height within 4 mm (0.15 in) in all loading conditions and the leveling function shall deactivate if the vehicle is overloaded. The side to side variation has to be maintained within 8 mm (0.31 in). After ignition is turned off, the module will stay awake for between 30 minutes and 2 1/2 hours. The system will exhaust pressure within 30 minutes after ignition is turned off to lower the vehicle after unloading. The leakage of the complete load leveling system shall not result in more than 1.4 mm (0.05 in) drop of rear suspension height at GVWR during a 24 hour period.
There are software Leveling Sequence Timers that detect conditions of excessive output at which no leveling is accruing. These timers shall keep track of conditions which cause excessive run time or no calibratable change in trim height. These timers are defined in more detail below.
Accumulator Timer
The primary purpose of the accumulator timer is to detect conditions in which excessive activity may occur. The conditions are generally as follows: in the compress mode the existences of pneumatic leaks in the system, in the exhaust mode the existence of pneumatic blockage or unloaded vehicle conditions. The accumulator shall keep track of the accumulated run time of the compressor. If the accumulator timer reaches its calibratable limit the output function will be disabled until the accumulator is reset. The accumulator timer will be reset with each transition into the RUN power mode or if the complementary output activation is required.
Progress Timer
The primary propose of the progress timer is to quickly detect conditions in which excessive output activity may occur at zero vehicle speed condition. If the Air Suspension System does not detect a calibratable change in position within a calibratable time period, the output function will be disabled. The timer will be reset with each ignition switch cycle into the RUN position.
Air Suspension Sensors
The air suspension sensor arm is attached to an armature that rotates inside a coil. The inductance of the coil, not the resistance, changes dependent on the position of the armature in the coil. The air suspension module determines the angle of the sensor arm by sending a pulse width modulated supply voltage through the coil and measuring the response time. The sensors must be calibrated to the correct D height and are not adjustable.
Rear Air Springs
The air springs are mounted in the frame in the same location were the coil spring is mounted for a vehicle without air suspension. Support pieces are affixed to the axle for the air springs.