Diagnostic Trouble Code Tests and Associated Procedures

Vehicle Dynamic Module (VDM) Diagnostic Trouble Code (DTC) Index

Vehicle Dynamic Module (VDM) Diagnostic Trouble Code (DTC) Index (Part 1):

Vehicle Dynamic Module (VDM) Diagnostic Trouble Code (DTC) Index (Part 2):

NOTE: Repair all other DTC's before C1725 and C1726. Repair DTC's C1990 and C1991 last.

Clearing DTC C1990 or C1991

NOTE: Before proceeding with the following steps, make sure that the 4WAS system is fully functional. The vehicle must pass the pneumatic test and have all 3 ride height sensors calibrated for these codes to clear.

1. Either start the vehicle or put vehicle on a battery charger to make sure of sufficient battery voltage.
2. Vent the vehicle down to the kneel position. (Having the key OFF, transmission in PARK, air suspension switch ON and all doors, the liftgate and the liftgate glass CLOSED will make the vehicle kneel.)

NOTE: Do not enter the vehicle during this process. The vehicle may not kneel or may kneel very little if the height of the vehicle is near the kneel position.

3. Pump the vehicle to the current calibrated trim height by turning the key to RUN, shifting to DRIVE, and then returning to PARK and closing all vehicle openings. Message center should show no openings ajar. Vehicle will then pump to the currently calibrated trim height.
4. Connect the diagnostic tool to the vehicle.
5. Run the pneumatic test. The tester will indicate if the vehicle has passed the test.

NOTE: Passing the pneumatic test does not eliminate the possibility of malfunctioning solenoid valves.

6. After passing the pneumatic test use the diagnostic tool to retrieve any DTC's. If C1990 or C1991 is present, go to Step 8 and calibrate the ride heights. Otherwise, go to Step 9.
7. Using the diagnostic tool, manually raise and lower the vehicle to the correct ride height on an alignment machine and calibrate the ride heights.

NOTE: Manual send mode on the NGS works better than the auto send mode.

8. Using the diagnostic tool, retrieve the DTC's and verify that all DTC's have been cleared.
9. Drive the vehicle and verify the repair. Verify that the "Check Suspension" message is not present. Make the system vent to kneel position and pump to trim height position several times while verifying system function.