P38A ABS & Traction Control Fault (2001 P38 4.0)

Wazagadoo said:

Hi everyone,

I need some help.

I've just got my P38 back from a "landrover specialist" after over 3 months, long story, but they were changed the wheel bearings and fixed the head gasket, but buggered the electrics and ended removing my LPG system along the way.

Anyway, now its showing ABS Fault & Traction Control faults. The ABS seems to be working (its stops anyway), but I'm not sure how I know if the pump etc is all working correctly. I've seen posts about the pumps and relays, but how do I know if the pump is working and which relay or switch is it?

The brake lights are working fine.

As they changed the bearing is there a good chance its just the sensor? If so how do I check the sensor?

Also, does anyone know what is supposed to be in the compartment next to the battery? The cover is now missing, but as I've never paid much attention before I don't know if there ever was anything in there!

Many thanks

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quavey said:

The compartment behind the battery on your 2001 Motronic V8 is supposed to be empty, on the earlier Gems cars it is the location of the ECU. The Motronic/Bosch ECU is behind/next to the EAS Box.

As for your TC and ABS errors, I have been chasing these my self. First job is to check it with diagnostics and see what error codes are there otherwise your fumbling in the dark. As Wammers has said its most likely an ABS sensor that has been disturbed or removed and refitted incorrectly. It does say that the sensor bush (little copper job that pushes into the hole first before the sensor goes through it) should be replaced if a sensor is REMOVED at any time. They are only a few pence so it could be something as simple as that so you could just check that all of the sensors are properly pushed home to where they should be. But best bet is diagnostics and go from there.

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Martian said:

Most ABS sensors are simple coils and they 'detect' very small changes in 'inductance' caused by ferrous metal coming into close proximity to the sensor tip, (the sensor is usually an electrical coil - but could be a more complex proximity sensor).

As well as each wheel having its own ABS Sensor there will also be an ABS 'Ring' affixed to each rotating wheel hub and the ring will either have regular holes drilled around the circumference, (in line with the position of the sensor), or the 'Ring' edge will be 'castelated', (just like teeth cut on a gear - but these 'teeth' will be square and not triangulated).

As the wheel rotates the holes, (or the square teeth), will pass by the sensor inducing a small voltage, (in the form of a rough square wave), that the ABS Computer then uses to analyse what each wheel is doing.

The sensor could be misaligned, open circuit, (break in the cable and/or connector), or it could be damaged, (physical trauma to sensor body due to it touching ABS Ring or due to rough handling), or the sensor ABS Ring could be damaged/misaligned.

The gap between the sensor and the ring is critical, (although I can no longer remember if the 'flux density' is inversely proportional to the square of the gap), but if the sensor is placed more than a few mm from its designated position there will, NOT be enough voltage induced to keep the ABS Computer happy - and will flag a fault.

If the sensor is too close to the ring it will 'detect' the presence of the ABS Ring at all times - thus not differentiating between the 'gaps' so NO square wave is produced and the ABS Computer will flag an error.

There is always ihe possibility that the ABS Computer, (or other associated components), are the cause of the fault but the sensor/ring is the usual culprit in most situations.

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