Lesson 4 – Diagnostics Discovery 3 / LR3

DISCOVERY 3 / LR3

System Checks
Fault Detection
The air suspension control module can store fault codes
which can be retrieved using the T4 diagnostic unit. The air suspension control module performs fault
detection and plausibility checks.
Diagnostic information is obtained via the diagnostic
socket which is located in the lower instrument panel Fault detection is limited to faults that the control
closing panel, on the driver's side, below the steering module can directly measure:
column. • Sensor electrical hardware faults
The diagnostic socket allows the exchange of • Valve electrical hardware faults
information between the various control modules on the
• Sensor and actuator supply faults
bus systems and T4 system or diagnostic tool.
• Bus failures
This allows the fast retrieval of diagnostic information
• Control module hardware errors
and programming of certain functions using the T4
system. Plausibility checks are checks on signal behavior, as
follows:

Height Changes

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Discovery 3 / LR3 Lesson 4 – Diagnostics

• Average height does not change correctly • Retain full functionality with no 'refinements'
• Height changes too slowly • Cross-link valves inoperative

Gallery Pressure • No compensation for uneven surfaces

• Does not increase fast enough when reservoir filling Pressure sensor faults, compressor faults, corner
requested valves stuck shut

• Increases when system is inactive • Road speed signal not available

• Too low when lifting is requested • Vehicle returns to on-road mode height when next
• Increases too rapidly when filling reservoir requested

• Does not decrease when gallery is vented • Levels at 'current' height

• Pressure varies too much when inactive Reservoir valve stuck open, exhaust valve stuck shut
if below on-road mode height, corner valves stuck
Compressor Temperature
open if above on-road mode height
• Sensor voltage too large - head and brush sensors
• Vehicle returns to on-road mode height when next
(short circuit to battery)
requested
• Takes too long to be readable after suitable
• Does not level at 'current' height
compressor run time - head and brush sensors
• Does not increase when compressor active - head Failure of multiple height sensors, cross-articulation
sensor only when driving, calibration corrupted

Sensor Activity • Vehicle lowers to bump stops

• Signal floating ABS module failure, CAN bus failure

• Constant articulation when moving • If the air suspension control module loses
communications with the ABS module or the ABS
When a fault is detected, the air suspension control
module reports a fault, the air suspension control
module will attempt to maintain a comfortable ride
module immediately returns to the 'default' height,
quality and where possible will retain as much
which is below the on-road ride height
functionality as possible.
• Once at the default height, the control module will
The system functionality depends on the severity of the
continue to level the vehicle at this height
fault.
• It is unlikely that the fault will be in the air
suspension control module
Fault Categories
• When the fault is repaired, the air suspension control
Faults are categorized into order of severity and effect module will resume full functionality but the error
on the system as follows: will remain in the control module memory

• 1 = Minor fault For major faults the control module will not level the
vehicle at the 'current' ride height.
• 5 = Major fault
The control module freezes height changes until it
Height sensor faults (hardware faults) and reservoir
receives a manual or automatic request for height
valve block failure
change.

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The control module will return to standard height if Detectable hardware errors include memory error,
possible and freezes once standard height is achieved. control module failure and calibrations errors.

If the suspension is above the on-road height and the

air suspension control module cannot lower the Fault Messages
suspension, all height changes will be frozen.
The air suspension has two methods which it can use
to inform the driver of a fault in the air suspension
ABS / CAN Failures
system; the air suspension switch LED's and the
instrument cluster message center.
The control module will issue a message on the high
speed CAN bus which is received by the instrument When minor faults occur and the air suspension control
cluster which displays a maximum advisable speed in module is able to level the vehicle to the 'current' ride
the message center. height, the air suspension switch LED's will display the
current ride height.
An immediate 'freeze' of the vehicle height is caused
by the following: If the air suspension control module suffers a major
failure and there is no air suspension control, all the
• Failure of more than one height sensor - vehicle on
control switch LED's will remain off.
bump stops
• Implausible articulation symptoms detected - vehicle If a fault occurs and the air suspension control module
on bump stops can determine the ride height and the vehicle is not
above on-road height, the driver will be notified via an
• Valve or solenoid failure - corner valve stuck open
'air suspension fault max speed 18.6 mph (30 km/h)'
below on-road height or exhaust valve stuck shut
warning in the message center.
above on-road height
• Stuck corner or whole vehicle (diagnosed using If the control module cannot determine the height of the
plausibility of the sensor inputs) vehicle, or the vehicle is above on-road height, cannot
be lowered and the vehicle speed is too high, an air
If height change is not possible, e.g. exhaust valve failed
suspension fault message is displayed.
closed at off-road height or compressor failed at access
height, the control module will not level or change If the vehicle is restricted to on-road height an air
height. suspension fault normal height only message is
displayed.
If the air suspension control module has a hardware
fault, the control module will disable all air suspension
functions.

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Discovery 3 / LR3 Lesson 4 – Diagnostics

Connector Information

Connector Pin Detail - C2030

Pin No Description Input or Output

1 Rear control valve - Cross link valve - positive (+) Output

2 Not used Not used

3 Not used Not used

4 Not used Not used

5 Air supply unit - Motor temperature sensor signal Input

6 Not used Not used

7 Air supply unit - Motor temperature sensor - Ground Input

8 Switch pack display - Raising LED Output

9 Switch pack display - Lowering LED Output

10 Switch pack display - On-road mode LED Output

11 Rear control valve - Cross link valve - negative (-) Input

12 Not used Not used

13 Not used Not used

14 Not used Not used

15 Not used Not used

16 Not used Not used

17 Switch pack display - Crawl mode LED Output

18 Switch pack display - Access mode LED Output

19 Not used Not used

20 Input Switch pack - Raise switch signal Input

Connector Pin Detail - C2320

Pin No Description Input or Output

1 Air supply unit voltage signal input from Air supply unit Input
relay

2 Reservoir control valve - Pressure sensor - 5 volt supply Output

3 Reservoir control valve - Pressure sensor - Signal Input

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Pin No Description Input or Output

4 Reservoir control valve - Pressure sensor - Ground Input

5 Air supply unit - Exhaust valve - Negative (-) Input

6 Air supply unit - Exhaust valve - Positive (+) Output

7 Not used Not used

8 Not used Not used

Connector Pin Detail - C2321

Pin No Description Input or Output

1 12V Permanent battery supply Input

2 Compressor temperature sensor - Signal Input

3 Front LH height sensor - 5 Volt supply

4 Front LH height sensor - Signal Input

5 Front LH height sensor - Ground Input

6 Air supply unit relay coil - positive

7 Air supply unit relay coil - ground Input

8 Reservoir control valve coil - positive (+)

9 Front control valve - RH corner valve - negative (-) Input

10 Front control valve - RH corner valve - positive (+)

11 Front control valve - LH corner valve - negative (-) Input

12 Front control valve - LH corner valve - positive (+)

13 Not used Not used

14 Front RH height sensor - 5V supply

15 Front RH height sensor - signal Input

16 Front RH height sensor - ground Input

17 Compressor temperature sensor - ground Input

18 Not used Not used

19 Not used Not used

20 Not used Not used

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Discovery 3 / LR3 Lesson 4 – Diagnostics

Pin No Description Input or Output

21 Reservoir control valve coil - negative (-) Input

22 Front control valve - cross link valve - positive (+)

23 Front control valve - cross link valve - negative (-) Input

24 Ground Input

Connector Pin Detail - C0867

Pin No Description Input or Output

1 Rear control valve - LH corner valve positive (+) Output

2 Rear control valve - LH corner valve negative (-) Input

3 Door status signal from CJB Input

4 Switch pack - Lower switch signal Input

5 Rear LH height sensor - 5v supply Output

6 Rear LH height sensor - Signal Input

7 Rear LH height sensor - Ground Input

8 Rear RH height sensor - 5v supply Output

9 Rear RH height sensor - Signal Input

10 Rear RH height sensor - Ground Input

11 Rear control valve - RH corner valve positive (+) Output

12 Rear control valve - RH corner valve negative (-) Input

13 Air suspension control - CJB signal Input

14 Switch pack display - LED ground Input

15 Switch pack display - LED high Output

16 CAN IN positive (+) Input

17 CAN OUT positive (+) Output

18 CAN OUT negative (-) Input

19 CAN IN negative (-) Output

20 12v ignition switch supply Input

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Control Schematic

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Discovery 3 / LR3 Lesson 4 – Diagnostics

Item Description Item Description

1. Fuse 26E (20 amp) 12. Exhaust valve solenoid

2. Fusible link 11E (30 amp) 13. Air suspension control module

3. Ignition switch 14. Central junction box (CJB)

4. Fuse 35P (5 amp) 15. Reservoir control valve

5. Fusible link 10E (60 amp) 16. Air suspension control switch

6. Air supply unit relay 17. Front valve block

7. Fuse 3E (5 amp) 18. Rear valve block

8. Air supply unit 19. RHR height sensor

9. Compressor temperature sensor 20. LHR height sensor

10. Motor 21. RHF height sensor

11. Motor temperature sensor 22. LHF height sensor

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