Pinpoint Test C: Vehicle Raises and/or Lowers Too Slowly Or Uneven Vehicle Height
Vehicle Dynamic Suspension
Pinpoint Tests
Pinpoint Test C: Vehicle Raises and/or Lowers Too Slowly or Uneven Vehicle Height
Normal Operation
The air suspension height sensor sends a voltage signal to the Vehicle Dynamics Module (VDM). The output ranges from approximately 4.5 volts at minimum height (when the vehicle is low or in full jounce) to 0.5 volt at maximum height (when the vehicle is high or in full rebound).
When the suspension height sensor indicates that the rear of the vehicle is lower or higher than trim height under normal driving conditions, the VDM will command the air compressor and air solenoid valves to either fill or vent the air springs depending on the input from the 2 height sensors. The air compressor sends the air to the air springs first through the drier then along the air tubes, passing through a Y-fitting and connections, through the air solenoid valves and finally to the air springs.
- DTC C1726 (Air Suspension Rear Pneumatic Failure) - With the ignition key in the RUN position, DTC C1726 will be set if the air suspension system attempts and fails to inflate (pump) or deflate (vent) a specified number of times.
- DTC C2002 (Pneumatic Test Failure) - This DTC indicates that the Pneumatic Test has failed to complete, possibly due to mechanical or electrical failure of the air suspension system. DTCs C1990 and/or C1991 will also set with this DTC.
This pinpoint test is intended to diagnose the following:
- Air leak(s)
- Air tube restricted or leak(s)
- Air tube(s)
- Mounting bracket(s)
- Air compressor drier
- Air spring solenoid valve(s)
- Height sensor(s)
- Air compressor
- Air spring(s)
- VDM
PINPOINT TEST C: VEHICLE RAISES AND/OR LOWERS TOO SLOWLY OR UNEVEN VEHICLE HEIGHT
NOTE: It may be necessary to vent air from the front air suspension air springs during this pinpoint test.
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C1 CHECK THE AIR SUSPENSION HEIGHT SENSORS
- Inspect the air suspension height sensors for correct installation.
- Inspect the air suspension height sensor mounting brackets for damage.
- While listening for air leaks, verify that all air tubes are fully seated.
- Are the air suspension height sensors, mounting brackets and air tubes OK?
Yes
GO to C2.
No
REPAIR as necessary. If one or both height sensor assemblies are installed or repaired, both height sensors must be calibrated. RESET the vehicle ride height. REFER to Ride Height Adjustments Ride Height Adjustments. CLEAR the DTCs. REPEAT the self-test.
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C2 CHECK THE AIR SUSPENSION HEIGHT SENSOR VOLTAGE PIDs
- Disable the air suspension system. Refer to Air Suspension System Disable/Enable Air Suspension System Disable/Enable.
- Disconnect the sensor arm linkage from both rear air suspension height sensors.
- Connect the scan tool.
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: DataLogger VDM.
- NOTE: The voltage will increase as the suspension is compressed.
- Slowly move the height sensors through their full range of travel up and down while monitoring the following PIDs:
- Left Rear Height Sensor Voltage (LR_HEIGHT)
- Right Rear Height Sensor Voltage (RR_HEIGHT)
- Do the voltages vary from approximately 0.50 volt and 4.50 volts?
Yes
CONNECT the sensor arm linkages to the height sensors. GO to C3.
No
INSTALL a new height sensor(s) and CALIBRATE both height sensors. REFER to Suspension Height Sensor Service and Repair. CLEAR the DTCs. RESET the vehicle ride height. REFER to Ride Height Adjustments Ride Height Adjustments. REPEAT the self-test.
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C3 VERIFY THAT THE REAR OF THE VEHICLE CAN BE RAISED
- Toggle the LR and RR air spring solenoid (LR_SOL and RR_SOL) active commands ON. Toggle the air compressor (COMPRESSR) active command ON.
- While monitoring both height sensor voltage PIDs, allow the vehicle to raise for 30 to 45 seconds.
- Toggle the VDM active commands OFF.
- Does the rear of the vehicle raise normally and hold the new height?
Yes
GO to C4.
No
GO to C5.
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C4 VERIFY THAT THE REAR OF THE VEHICLE CAN BE LOWERED
- Toggle the LR and RR air spring solenoid (LR_SOL and RR_SOL) active commands ON.
- Toggle the vent solenoid (AsVent) active command ON.
- NOTE: Allow the rear to lower for 30 seconds.
- Toggle all active commands OFF.
- Does the rear lower normally?
Yes
CARRY OUT the Pneumatic Test and VERIFY system operation. Inspection and Verification
No
GO to C7.
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C5 CHECK OPERATION OF THE AIR COMPRESSOR
NOTICE: The Vehicle Dynamics Module (VDM) limits the air compressor run time. If the air compressor overheats, it will not restart until it cools down. The ignition switch must be in the OFF position to allow the compressor thermal switch to cool.
- Toggle the air compressor (COMPRESSR) active command ON.
- Does the air compressor run (slight buzzing noise from RF corner of vehicle)?
Yes
TOGGLE the COMPRESSR active command OFF. GO to C6.
No
TOGGLE the COMPRESSR active command OFF. GO to Pinpoint Test J. Pinpoint Test J: The Air Compressor Is Inoperative
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C6 CHECK THE AIR COMPRESSOR PRESSURE OUTPUT
NOTICE: The Vehicle Dynamics Module (VDM) limits the air compressor run time. If the air compressor overheats, it will not restart until it cools down. The ignition switch must be in the OFF position to allow the compressor thermal switch to cool.
NOTE: If fluid is present when disconnecting an air tube, clear the air tubes. Refer to Air Line Fluid Purge Air Line Fluid Purge procedure. Check the compressor air drier for water or the front air spring for oil.
- Disconnect the air tube at the air compressor drier.
- Connect an air pressure gauge (1,723 kPa [250 psi] maximum reading) with common fittings to the air drier.
- NOTE: The vehicle will lower quickly.
- NOTE: When toggling the compressor ON, the vent solenoid will open as well. To prevent the vent solenoid from opening during this test, first toggle a single spring solenoid ON, then toggle the compressor ON.
- Toggle the LR spring solenoid (LR_SOL) active command ON.
- Toggle the air compressor (COMPRESSR) active command ON.
- Operate the air compressor for 30 seconds then toggle the COMPRESSR active command OFF.
- Did the compressor produce 1,034 kPa (150 psi) within 30 seconds?
Yes
GO to C8.
No
INSTALL a new air suspension compressor. REFER to Air Suspension Compressor Service and Repair. CARRY OUT the Pneumatic Test. VERIFY system operation. Inspection and Verification
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C7 CHECK THE PNEUMATIC SYSTEM - VENT THE AIR SPRINGS
NOTE: If fluid is present when disconnecting the air tube, clear the air tubes. Refer to Air Line Fluid Purge Air Line Fluid Purge. Check the air compressor drier for water or the air compressor for oil contamination.
NOTE: The rear springs must be partially inflated in order to carry out this test. Add air as necessary.
- Disconnect the air tube at the air compressor drier.
- Toggle the LR air spring solenoid (LR_SOL) active command ON. This will activate both the LR and RR air spring solenoids.
- Does the air vent from the air compressor drier air tube?
Yes
TOGGLE the LR_SOL active command OFF. GO to C9 .
No
TOGGLE the LR_SOL active command OFF.
CONNECT the air tube to the air compressor drier. GO to C8.
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C8 CHECK THE PNEUMATIC SYSTEM - AIR TUBE
NOTE: If fluid is present when disconnecting the air tube, clear the air tubes. Refer to Air Line Fluid Purge Air Line Fluid Purge. Check the air compressor drier for water or the air compressor for oil contamination.
- Disconnect the suspected rear air spring solenoid air tube.
- Connect the vacuum tester to the air tube and try to pull a vacuum.
- Can a vacuum be developed?
Yes
REPAIR or INSTALL a new air tube. CLEAR the DTC. REPEAT the self-test.
No
GO to C11.
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C9 CHECK THE VENT SOLENOID OPERATION
- Disconnect the air tube at the drier.
- Connect the vacuum tester to the drier and try to pull a vacuum.
- Toggle the vent solenoid (AsVent) active command ON.
- Try to pull a vacuum again.
- Can a vacuum be developed with the As Vent active command OFF and no vacuum developed with the As Vent active command ON?
Yes
INSTALL a new VDM. REFER to Vehicle Dynamics Module (VDM) Service and Repair. CLEAR the DTCs. REPEAT the self-test.
No
If a vacuum can be developed with the vent solenoid OFF, GO to C10 .
If a vacuum cannot be developed with the vent solenoid OFF, INSTALL a new air compressor. REFER to Air Suspension Compressor Service and Repair.
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C10 CHECK THE AIR TUBE AND CONNECTIONS
- Check the air tube and connections between the vacuum tester and the air compressor.
- Are the air tube and connections OK?
Yes
INSTALL a new air compressor. REFER to Air Suspension Compressor Service and Repair. CLEAR the DTC. REPEAT the self-test.
No
REPAIR the air tube. GO to C9.
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C11 CHECK THE SPRING SOLENOID VALVE
NOTE: The air springs must be inflated for this test.
- Disconnect the air tube at the air spring solenoids.
- Toggle the LR and RR air spring solenoid (LR_SOL and RR_SOL) active commands ON.
- Does air vent from the solenoids?
Yes
TOGGLE the active commands OFF. INSTALL a new VDM. REFER to Vehicle Dynamics Module (VDM) Service and Repair.
No
TOGGLE the active commands OFF. INSTALL a new air spring solenoid. REFER to Air Spring Solenoid Valve Service and Repair.
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