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Home >> Mercury >> 2011 >> Grand Marquis V8-4.6L >> Repair and Diagnosis >> Steering and Suspension >> Suspension >> Suspension Control ( Automatic - Electronic ) >> Testing and Inspection >> Pinpoint Tests >> Pinpoint Test C: DTC C1726

Pinpoint Test C: DTC C1726




Vehicle Dynamic Suspension

Pinpoint Tests

Pinpoint Test C: DTC C1726

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 air suspension height sensor indicates that the rear of the vehicle is lower than trim height under normal driving conditions, the air compressor will turn on and pump compressed air into the air springs. When the sensor indicates that the rear of the vehicle is raised above trim under normal driving conditions, this will cause the air to be vented from the air springs to lower the vehicle back to its trim height level.

- 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.

This pinpoint test is intended to diagnose the following:
- Height sensor brackets
- Air tube
- Air suspension height sensor
- Air spring solenoid valve
- Air suspension compressor drier
- Air suspension compressor
- VDM

PINPOINT TEST C: DTC C1726

NOTE: Repair all other DTCs before repairing DTC C1726.

NOTE: It may be necessary to partially vent air from the air springs during this pinpoint test.

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C1 CHECK THE AIR SUSPENSION HEIGHT SENSOR MOUNTING


- With the vehicle in NEUTRAL, position it on a hoist. Refer to Jacking and Lifting Service and Repair.
- Check the air suspension height sensor for correct installation at the upper and lower ball stud brackets.
- Check the air suspension height sensor mounting brackets for damage.
- Are the air suspension height sensor and mounting brackets OK?

Yes
GO to C2.

No
REPAIR as necessary. CLEAR the DTC. REPEAT the self-test.

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C2 CHECK THE AIR SUSPENSION HEIGHT SENSOR (RR_HEIGHT) PID


- Lower the vehicle.
- Disconnect the lower end of the air suspension height sensor link.
- Connect the scan tool.
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: DataLogger VDM.
- Monitor the RR_HEIGHT PID while slowly moving the air suspension height sensor through its full range of motion.
- Does the height sensor PID display vary from 0.5 volt to 4.5 volts?

Yes
CONNECT the lower end of the height sensor link. GO to C3.

No
INSTALL a new air suspension height sensor. REFER to Suspension Height Sensor Service and Repair. CLEAR the DTC. REPEAT the self-test.

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C3 VERIFY THAT THE REAR OF THE VEHICLE CAN BE RAISED


- Record the voltage level for the air suspension height sensor.
- Enter the following diagnostic mode on the scan tool: DataLogger VDM.

- NOTE: If the air spring solenoids are not activated before the compressor is activated, the vent solenoid will automatically activate.

- Toggle the following output commands ON:
- Left Rear Air Spring Solenoid (LR_SOL)
- Right Rear Air Spring Solenoid (RR_SOL)
- Air Compressor (COMPRESSOR)
- Allow the rear of the vehicle to raise for only 30 seconds.
- Does the rear of the vehicle raise and hold the new height?

Yes
TOGGLE all output commands OFF. GO to C4.

No
TOGGLE all output commands OFF. GO to C5.

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C4 VERIFY THAT THE REAR OF THE VEHICLE CAN BE LOWERED


- Enter the following diagnostic mode on the scan tool: DataLogger VDM.
- Toggle the following output commands ON:
- Left Rear Air Spring Solenoid (LR_SOL)
- Right Rear Air Spring Solenoid (RR_SOL)
- Air Suspension Vent Solenoid (AsVent)
- Allow the rear to lower until the rear air suspension height sensor voltage reading matches the one recorded in Step C3 or until 30 seconds have passed.
- Does the rear of the vehicle lower?

Yes
TOGGLE all output commands OFF. CLEAR the DTCs. REPEAT the self-test and CARRY OUT the Pneumatic Test. Component Tests and General Diagnostics

No
TOGGLE all output commands OFF. GO to C7.

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C5 CHECK THE AIR COMPRESSOR (COMPRESSOR) OUTPUT COMMAND


NOTICE: Do not allow the air compressor to run for more than 3 minutes. The air compressor could overheat and stop operation due to an internal temperature sensitive thermal breaker.

- Enter the following diagnostic mode on the scan tool: DataLogger VDM.
- Toggle the air compressor to ON.
- Does the air compressor run?

Yes
TOGGLE all output commands OFF. GO to C6.

No
TOGGLE all output commands OFF. GO to Pinpoint Test I. Pinpoint Test I: 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 the air tube, clear the air tubes. Refer to Air Line Fluid Purge Air Line Fluid Purge. Check the compressor air drier for water or the air compressor for oil contamination.

- Disconnect the air tube at the air compressor drier.
- Connect an air gauge with a maximum reading of 1,723 kPa (205 psi) to the air drier using common fittings.
- Enter the following diagnostic mode on the scan tool: DataLogger VDM.
- Toggle the LR and RR air spring solenoids to ON.

- NOTE: If the air spring solenoids are not activated before the compressor is activated, the vent solenoid will automatically activate.

- Toggle the following output commands ON.
- Left Rear Air Spring Solenoid (LR_SOL)
- Right Rear Air Spring Solenoid (RR_SOL)
- Air Compressor (COMPRESSOR)
- Operate the air compressor for 30 seconds then toggle the air compressor OFF.
- Did the compressor produce 896 kPa (130 psi) within 30 seconds and hold the developed pressure?

Yes
TOGGLE all output commands OFF. GO to C8.

No
TOGGLE all output commands OFF. INSTALL a new air suspension compressor. REFER to Air Suspension Compressor Service and Repair. CLEAR the DTC. REPEAT the self-test.

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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.
- Enter the following diagnostic mode on the scan tool: DataLogger VDM.

- NOTE: The vehicle will lower quickly.

- Toggle the following output commands ON:
- Left Rear Air Suspension Solenoid (LR_SOL)
- Right Rear Air Suspension Solenoid (RR_SOL)
- Does the air vent from the air compressor drier air tube?

Yes
TOGGLE all output commands OFF. GO to C9.

No
TOGGLE all output commands 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.

- 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
INSTALL a new air spring solenoid valve. REFER to Air Spring Solenoid Valve Service and Repair. CLEAR the DTC. REPEAT the self-test.

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C9 CHECK THE VENT SOLENOID (AsVent) PID


- Disconnect the air tube at the drier.
- Connect the vacuum tester to the drier and try to pull a vacuum.
- Enter the following diagnostic mode on the scan tool: DataLogger VDM.
- Toggle the AsVent output command to ON.
- Try to pull a vacuum again.
- Can a vacuum be developed with the vent solenoid OFF active command and no vacuum developed with the vent solenoid ON active command?

Yes
TOGGLE all output commands OFF. INSTALL a new VDM. REFER to Vehicle Dynamics Module (VDM) Service and Repair. REPEAT the self-test.

No
TOGGLE all output commands OFF. If a vacuum cannot be developed with the vent solenoid OFF, GO to C11.

If a vacuum can be developed with the vent solenoid OFF, GO to C10 .

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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. CLEAR the DTC. REPEAT the self-test.

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C11 CHECK THE AIR COMPRESSOR DRIER


- Remove the air tube at the air compressor drier.

- NOTE: Under normal operating conditions, the compressor drier should pull a vacuum and then slowly leak down. A drier is defective if it will not pull a vacuum or if it pulls a vacuum but fails to slowly leak down.

- Connect the vacuum tester to the air compressor drier and try to pull a vacuum.
- Can a vacuum be developed, followed by a slow leak down?

Yes
INSTALL a new air compressor. REFER to Air Suspension Compressor Service and Repair. CLEAR the DTC. REPEAT the self-test.

No
INSTALL a new air compressor drier. REFER to Air Suspension Compressor Drier Service and Repair. CLEAR the DTC. REPEAT the self-test.

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