BRAKES: DESCRIPTION AND OPERATION (page 4 of 5)

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