Discovery II
BRAKES
DESCRIPTION AND OPERATION
70-23
Typical disabled times
Diagnostics
While the ignition is on, the diagnostics function of the SLABS ECU monitors the system for faults. In addition, the
return pump is tested by pulsing it briefly immediately after the engine starts provided vehicle speed exceeded 4.4
mph (7 km/h) during the previous ignition cycle. If a fault exists in a warning lamp circuit, the lamp will not illuminate
during the lamp check at ignition on but, provided there are no other faults, the related function will otherwise be fully
operational. If a fault is detected during the power up, the SLABS ECU stores a related fault code in memory and
illuminates the appropriate fault warning lamps. If a fault is detected later in the drive cycle, the SLABS ECU also
sounds the audible warning three times.
Fault codes and diagnostic routines can be accessed by connecting Testbook to the vehicle's diagnostic connector
in the driver's footwell.
Warning lamp fault operation
After detecting a fault, the SLABS ECU selects an appropriate default strategy which, where possible, retains some
operational capability. A shuttle valve switch fault and throttle position signal fault are classified as permanent faults.
If a permanent fault is detected, the related warning lamp illumination and default strategies are automatically
employed in subsequent ignition cycles, even if the fault is intermittent, until the fault has been rectified and cleared
from memory. If a non permanent fault is detected, the related warning lamp illumination and default strategies will
only be employed in subsequent ignition cycles if the fault is still present.
After rectification of an ABS sensor fault, the ABS and ETC functions are disabled, and the ABS warning lamp remains
illuminated after the lamp check, until vehicle speed exceeds 9.4 mph (15 km/h) (to allow additional checks to be
performed).
Vehicle speed, mph (km/h)
Time, minutes
1.3 (2)
40
12.5 (20)
33
15.6 (25)
17
25.0 (40)
9
31.3 (50)
6
Item
Check
Warning lamp
ABS
Brake
ETC
HDC
fault
ABS sensors
Resistance (to check status)
On
On
On
On
Brake lamps relay
Open/Short circuit
Off
Off
Off
On
Engine data
Sticking throttle, signal failure, data corruption
Off
Off
On
On
Inlet solenoid valves
Open/Short circuit
On
On
On
On
Outlet solenoid valves
Open/Short circuit
On
On
On
On
Reference earth
Connection to earth
On
On
On
On
Return pump monitor
Correct pump operation
On
On
On
On
Return pump relay
Open/Short circuit
On
On
On
On
Shuttle valve switches
Open/Short circuit
On
On
On
On
SLABS ECU
Internal failure
On
On
On
On
Supply voltages
Range (10 to 16 V)
On
On
On
On