Initial Inspection and Diagnostic Overview
ASCM PRE-DIAGNOSTIC TROUBLESHOOTING PROCEDURE
For a complete wiring diagram, refer to the Wiring Information.
NOTE:
Repair any Electrical or Communication DTCs before continuing with this diagnostic procedure.
Theory of Operation
Air mass is measured by the Air Suspension Control Module (ASCM). If it is low then the compressor is turned on to pull in outside air through a drier and into the reservoir. It does this at a rate of 10 liters every two minutes. Then right after that five liters of air are released back through the drier and out through the exhaust hose. This is done to regenerate the drier. Air mass makeup only occurs while in the normal operation mode (out of "In Plant Mode").
When all four LED's are flashing the ASCM system is "In Plant Mode" or "Service Mode" and normal leveling is disabled. If two LED's are illuminated in a staggered sequence the system is in normal operation.
NOTE: Diagnose and repair any system voltage DTCs before continuing with this test.
Diagnostic Test
1. CHECK FOR OVERUSE DTCS PRESENT
NOTE: Repair all electrical and communication DTCs before continuing with this diagnostic procedure.
Turn the ignition on.
1. With the scan tool, record and erase the DTCs.
2. Cycle the ignition from off to on.
3. With the scan tool, read the DTCs. NOTE: If any of these DTCs are present DTC C15A1-00-UNABLE TO OBTAIN DESIRED RIDE HEIGHT will set.
4. Overuse DTC list:
- C155E-92
- C1562-92
- C1562-98
- C1566-92
- C1567-92
- C1568-92
- C1569-92
- C159F-92
- C15A0-92
- C15C0-98
Are any of the above DTCs present?
Yes
- Go To 2
No
- Use the table above for the Air Suspension conditions and follow the action procedures to repair the vehicle.
2. AIR SUSPENSION CONDITION IS PRESENT
1. Turn the ignition off.
2. Check for any Service Information Technical Service Bulletins (TSB) that may apply.
3. Check the ASCM Fuse M2 (20A) and the Air Compressor Fuse J1 (40A).
4. Inspect for the following:
- doors or liftgate open.
NOTE: Doors and Liftgate statusare ignored when system is in diagnostic mode.
- pinched or damaged lines.
- damaged or leaking air-spring.
- sensor linkages are installed and connected correctly.
- no water present in hose or filter.
- blocked air compressor intake line.
5. Turn the ignition on.
NOTE: With the scan tool select metric units for proper accuracy.
With the scan tool, generate a vehicle scan-log with the environmental conditions.
NOTE: The acceptable amount of air is between 165 and 221 bar-liters (2392.5 to 3204.5 psi-liters).
With the scan tool, perform the system Air Mass routine and record the amount of air in the system.
Were any problems found or Air Mass out of range?
Yes
- Go To 3
No
- Go To 6
3. AIR SUSPENSION ON-BOARD AIR MAKEUP PROCEDURE
NOTE: A properly functioning system will make up for small leaks.
Start the engine.
1. With the scan tool, under Miscellaneous Functions run the "Air Mass Routine".
2. Record the Air Mass value.
3. Listen for Air Compressor to run (approx.15 sec).
4. Air Compressor will stop for (approx. 7 sec) while discharging exhausted air.
5. After three cycles of the system run the "Air Mass Routine".
6. With the scan tool, perform the system Air Mass routine and record the amount of air in the system.
Did the Air Mass increase?
Yes
- Go To 4
No
- Go To 6
4. AIR SUSPENSION RIDE HEIGHT ROUTINE
1. With the scan tool, under Miscellaneous Functions run the "Air Ride Height Routine".
Is the Air Suspension system operating correctly?
Yes
- Test complete, the condition or condition that originally set this DTC is not present at this time.
- Perform the ASCM VERIFICATION TEST. ASCM Verification Test.
No
- Go To 6
5. TERRAIN SWITCH
1. Turn the ignition on.
2. With the scan tool, monitor the Terrain Switch while pressing the up and down buttons on the Terrain Switch.
Does the Terrain Switch operate correctly?
Yes
- Go To 6
No
- Replace the Terrain Switch.
- Perform the ASCM VERIFICATION TEST. ASCM Verification Test.
6. AIR SUSPENSION CONTROL MODULE (ASCM)
1. With the scan tool, erase the DTCs.
2. Start the vehicle.
3. With the scan tool, read the DTCs.
Does the DTC remain active?
Yes
- Replace the Air Suspension Control Module (ASCM). Air Suspension Control Module - Removal.
- Perform the ASCM VERIFICATION TEST. ASCM Verification Test.
No
- Test complete, the condition or condition that originally set this DTC is not present at this time.
- Perform the ASCM VERIFICATION TEST. ASCM Verification Test.