1995 V8 Disco SBS Failure - How to trouble shoot

Hello to the wise and wonderful
My 1995 V8 Disco has developed a problem that isn’t supposed to happen. The SBS fails UNSAFE! Taking the beast out for it annual MOT last week, put my foot on the brake at the first road junction, the anti skid activated and reduced the braking down to almost zero. No light!. Dry Road! No Skidding! No Wheel anywhere near lockup! A genuine brown trouser moment!
The problem is how to trouble shoot this system, I am not to sure of the value of taking it in to the local Landrover Dealer as the diagnostics would not be very meaningful unless the equipment is connected to the vehicle when the problem occurs, what sensor triggered the problem. I have made the assumption that it must be one of the fronts because of the loss of retardation? (I hope my thinking is not to flawed here!)
Is there any gismo available that can indicate the source of the trigger? If I take it into Landrover will the diagnostics be meaningful?
The truck has now done 170K but back at 26k it did have a problem with the ABS light on and this was fixed by Landrover replacing the nearside forward sensor.
Last question, is it possible to remove and reinstall the sensors successfully?
Any ideas gratefully appreciated.

Firstly :welcome2: to the Forum, second perhaps you can rewrite your first paragraph so I can understand it.
I'm sure taking your disco into Landrover or an indipendent LR workshop the diagnostics be meaningful.

Hi Discool

Thanks for responding and sorry that you did not understand the problem.
It is simply that when applying the brakes and expecting normal braking that ABS activates as if it detects a skid and reduces the braking accordingly. Very scary!

I am trying to establish how to trouble shoot the wheel sensors to see which one is incorrectly sensing a skid condition.:doh:

Thanks

:doh:Hello

Not making much progress on this one and it is interesting to find that the problem is not uncommon!

I am still trying to understand how this system works. Am I correct in assuming that because the ABS self test is good then the system is basically sound and what I am looking for is an intermittant problem.

I am completing the usuall continuity test at the moment looking for ground and the 1150ohms and clean up all the connectors as part of the process.

But what is next?

How do I nail down the source of the problem, presumably one of the 4 inputs to the ABS disagrees to cause the ABS to activate, is there anything else in the system that would activate the ABS when brakes are applied?

My next test after putting the system back together will be to connect DVMs to each wheel sensor and measure the output.

Does anyone know what the outputs are on the ABS test connector (blue block under the drivers dash) Can I connect a scope and view wave forms etc.

Lastly, is there an easy way of removing the sensors, they are really tight on my D1, so much so that I have concerns about damaging them. They are currently being soaked in freeing oil.

Any ideas much appreicated.

Hi here is a explanation of how the warning lamp works .
If all is OK the warning light will come on when you switch the ignition to position 2 , after two seconds it will go off for approx half a second and then come back on again and remain on until you drive forward and exceed 5 mph , it will then go out .
The system will "initially" check when powered up and tell you such. It'll run a check through the wiring, sensors etc and say all okay... during movement the system will check to see its getting speed signals ( voltage generation ) from the wheel sensors ie a voltage generated above 5 mph.
If the light remains on after driving forward you have a current and active fault with your system

If the light comes on any time you are driving you have just received a current and active fault .

The flash on/off and stay on again when stationary when just switching on confirms you currently have no stored faults in the ECU.

If it does NOT flash on and off but stays on you have a fault that is stored in the ABS ECU .

Then if the light then goes out when driving it is an old fault that has either corrected it self or been fixed by someone and the fault codes not cleared from the ECU or it is an intermittent fault.

If the light does not go out you have a current and active fault and you may not have full ABS operation.

I am 100 % sure of this as I have just spent a lot of time researching WABCO C ABS faults as I had a problem very recently on my Disco which I managed to fix . I will post later on a method of obtaining the fault codes for the ABS for you
Regards Jonathan

Discovery I - ABS Blink Code Procedure

This Procedure is only for the Discovery Series I vehicles!

If an external diagnostic tool is not available, the following procedures can be carried out to determine the cause of an ABS fault message. The faults can be retrieved by jumping a series of pins and reading the series of blink codes through the ABS warning lamp.

First, you will need to create a jumper wire out of something close to 16 gauge wire. Locate the Testbook diagnostic connector located under the dash panel. Connect the Jumper wire to pins 5 and pins 15. Turn the key to the second position. 5 seconds after the ignition is turned to the second position, the Anti-Lock warning light will extinguish. When the light extinguishes, this signals the start of the blink code cycle. The code below indicates the beginning of the fault retrieval blink sequence.

The second series of blink codes, will describe the actual fault code number. The first part of the code is signaled by a pause of 2.5 seconds. Immediately following is a series of short flashes then a long pause. The number of short flashes will equal the first digit in the stored fault code.

The second digit in the fault code is determined after a 2.5 second pause. This pause occurs between the first and second digit blink signals. After the 2.5 second pause, there will be another series of short flashes. The number of flashes corresponds to the second digit in the stored ABS fault code. After the second digit is signaled, there will be a pause of 2.5 seconds before the system repeats the stored fault code. This allows for you to see the code again if it was missed the first time. I would also suggest watching the sequence again just to make sure that you got it right the first time through. The diagram below indicates a stored fault code of 2-2.

The above sequence will continue until the jumper wire is removed. Once the jumper wire is removed, that single fault code will be cleared. Do not remove the jumper until the fault code has been recorded. Otherwise is cleared and gone when the jumper is removed.
To view all the faults stored in the ABS computer, repeat the above procedure starting with inserting the jumper wire. If there are no remaining faults, there will be a long 7.5 second pause after the start phase.


This is for the standard J1962 OBD connector. I will post later details of which pins for the blue connector . Regards Jonathan

This was copied prom another post I

If after you have read this and your still unsure, please, please, please do not try it, get some expert advice.

ABS Diagnostics

But there's an easy DIY way to read and reset these diagnostic codes. And you don't need a testbook computer - all you need is a bit of wire, or a paperclip!

There is nothing new in this document. All I have done is gathered together various other Internet documents, and added some notes on where the various connectors are on my Discovery. Many of the internet document relate to US-spec vehicles, where the components are located elsewhere.

My Disco is a UK-spec 1995 300 TDi XS.

The ABS ECU itself is a standard Bosch/Wabco part. If you do some googling, you'll find that the same techniques and codes apply to many other vehicles that use this unit.

First of all, we need to find the ABS warning light relay. On mine, it's in the passenger footwell, under the glove compartment. Lever out the 3 press-in studs, and the trim panel can drop. There are half a dozen relays in there. The one we're looking for is (on mine!) nearest to you, but in the second row, "behind" some others. Difficult to explain, but obvious when you get in there. The relay bases slide onto brackets, push them about an inch "away from the wires" and they'll come free.

The one we're looking for has a green base, and has 2 black wires, 1 black/green wire and 1 brown/red wire.

Disconnect this relay - pull it out of the socket.

Now we need to find the ABS diagnostic connector. This is where I struggled. All of the internet info says it's a blue connector under a seat, but that's just on US-spec vehicles. Rave says it's a 5-pin connector near the fuse box. But I couldn’t find that either. I believe that earlier (pre-95) models used this, but later ones moved it to the main diagnostic connector. This is a 16-pin socket, located under the steering wheel, just above the clutch. You don't need to remove any trim panels to get to it - although you may want to pop out the panel it's mounted on - it's not immediately clear how the pins are numbered, so look at the colours of the wires.

The 2 pins we're interested in are pin4 (black) - ground, and pin15 (red/green) which goes to the ABS unit. If the internet sources are to be believed, the abs diagnostic wire may be black/pink on some models,

and on the 5-pin connector we're interested in pins 2 and 5. But this has not been verified.
You need some way of bridging the 2 pins. A paper clip or a piece of solid-core wire is ideal.

Now, we're ready to go.

Make sure the relay is disconnected. Turn on the ignition. The ABS warning light should come on, as usual.

Bridge the 2 pins on the diagnostic connector.

After 5 seconds, the ABS warning light should go out. It will then flash a pattern. From this, we can obtain the 2-digit fault code.

first of all there will be 2 slow flashes - one longer than the other, with a gap of about 2 seconds.

Then the interesting bit. The lamp will then flash, at about one flash per second. Count these flashes - that's your first digit.

Then a pause

Then it will flash out the second digit.

This sequence will then repeat indefinitely (start, digit 1, digit 2).

If you disconnect the link when the lights are flashing, it will clear the fault. Reconnecting it will show the next stored fault. If you have patience, you can read out and clear the entire contents of the ABS memory.

In my case, all of the stored fault codes were the same - 2 flashes, then 12 flashes. So you look up 2-12 in the table below, and find "air gap, right hand front wheel speed sensor." This ties in with my own experience - I know that re-seating that sensor will temporarily cure my fault!

I will try and post some code definitions later on . I have the manufactures maintenance manual .


Please be very careful what you do and check what I say against a google search on the internetIf you get the pin identfication wrong I am not sure if you could do some damage

Regards Jonarthan

have a look here it might help you
http://www.meritorhvs.com/MeritorHVS_Documents/mm38.pdf