ABS warning light function explantion

ABS WARNING LIGHT FUNCTION EXPLANTION

Model

Range Rover Classic All ABS Derivatives

Affected vehicles

Upto 624756

Date

1995-01-30

Reference

30/01/95

Bulletin text

ABS Warning Light Function Explanation

MODEL

Range Rover Classic All ABS Derivatives

DETAIL

For the benefit of our customers, where the ABS Electronic control unit has to be replaced on pre 1993 model year vehicles, We have introduced the 1993 model year ABS electronic control unit (NTC 8474) as a replacement, This is fully compatible with the early vehicles, and is an enhancement over the early Electronic control units.

A brief explanation of the revised ABS light function and features are detailed below.

The purpose of the ABS light is to warn the driver when the ABS is not functional. The light comes on when the vehicle is initially switched on using the ignition key and stays on until the vehicle is driven faster than 7 Kph. This is the only time the light is illuminated without indicating a problem.

The reason for the light operating in this way is because the ABS ECU cannot detect a fault if all wheelspeed sensors are connected but not working. The system would simply be unaware that the vehicle is moving, this mean that the ABS light must be lit until wheelspeed sensor signals are received, it also conveniently serves as a bulb check function.

Vehicles which switch off the ABS light before moving off or do not illuminate the warning lamp at all, are at risk of having inoperative ABS without any warning for the driver.

For ‘1993 model year’ Range Rover a feature was added to indicate whether or not the ABS ECU has recorded any faults which have not been checked or repaired. This is done by switching the ABS light off and on again once for half a second after the ignition is switched on and the ECU has completed its self checks, this will happen during the time that the light is on between switching on and driving above 7 Kph. The function will also enable ‘MOT’ testers to check the ABS without driving the vehicle.

The sequence of events in a Range Rover Classic fitted with the latest ECU (NTC 8474) with no faults existing, or stored in the memory, are as followed:

Ignition on ABS light comes in for 1.3 to 2 seconds. ABS light goes out for 0.5 to 0.625 seconds. ABS light comes back on until the vehicle speed exceeds 7Kph.

No action required for information only

30/01/95

70/01/95/EN

AFFECTED VEHICLES

LP LH Upto 624756 LJ LD