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She's just failed because the "ABS light comes on when brakes applied" apparently on the rolling road whilst testing the braking force. In all other respects the system works normally, ABS comes on when ignition on, stay illuminated until a few MPH registered and then no sign of it unless braking hard enough on a loose enough surface to initiate brake modulation which of course i can feel. But just realised that the brake pressure pump comes on as soon as I touch the brake pedal, and when pressed hard the ABS light can come on for a second or two whilst the pump is pumping.
So I'm assuming its the pressure vessel that's gone?

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Surely they are not supposed to do 'rolling road' brake testing with 4X4s for this specific reason ??

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Accumulator time. 5 minute job. I used a syringe to ensure the new one was completely full and also the union it screws into. No need to bleed the brakes, at least I didn’t need to.

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Agreed, it's coming on because the ABS is operating. Any car with permanent 4x4 (and that includes things like Audis) they MUST NOT use a two wheel rolling road brake tester. Not only can it bugger the car but also the tester. Tell the tester to do it again after he's read the testers manual https://www.gov.uk/guidance/mot-inspection-manual-for-private-passenger-and-light-commercial-vehicles/1-brakes. If they try to test the parking brake on a roller it will also fail as it tests one wheel at a time but as the brake is on the propshaft, the side being tested will rotate one way while the other one rotates the other way and the test shows zero braking performance.

Pump coming on more than it should means the accumulator is getting weak, but that won't cause the ABS light alone to come on, the TC light would come on too if the pressure drops too much.

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Typical that it should choose to go on the morning of the day of an M.O.T! Sometimes I don't think she appreciates me. I've gone for a Rimmer Bros OEM replacement but £100!, for others next time if anyone knows of cheaper generic alternatives please chime in here......

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I assume you are talking about the accumulator? If the pump runs every time you press the brake pedal, it is getting weak but unless the warning lights come on if you do it when you are stationary, it still has some life left in it. You should be able to press the brake pedal 3 or 4 times before the pump cuts in. As for the MoT failure, that was nothing to do with the accumulator, that was the ABS kicking in as it was tested on a 2 wheel roller. It was applying the brakes on the wheels that were turning faster than the others. So with two wheels not moving and two that were, it will kick in and apply the brakes to the ones that are turning. The warning light coming on tells you the ABS is doing what it was designed to do.

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Jeez, great way to feck up the drive train.
Must never use rollers. They should be using a decelerometer that goes in passenger footwell.

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This sounds like a great way to knacker the viscous coupling in the transfer case.

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Dear All,
As its the original ABS pump if reservoir needed replacing ,likely pump will too, but a bit pricey. How long should it pump for to get the pressure up, a few seconds, longer. This is after standing for a week?

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After standing for a week, it should run for anything up to a minute. Once it is up to pressure, you should be able to press the brake pedal 3 or 4 times before the pump cuts in again. That shows the accumulator is good. If it takes a long time to pressurise but cuts in after every press of the brake pedal, that shows the accumulator may be OK but the pump is weak or the brakes need bleeding. Air in the power circuit doesn't give a spongy pedal, it gives a slight delay between pressing the pedal and the brakes coming on (as the fluid has to compress the air in there before it can cause anything to move). If the warning light comes on when you press the brake pedal, the accumulator is completely shot.

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I'm surprised they managed to get a two wheel rolling road actually rolling. I thought it would simply turn the other wheels and drive itself off the rollers?

Seriously not a good thing to try though. That is why Land Rover say to remove prop shafts should you ever use a towing dolly.

My MOT chap said to me, long time since I tested one of these, does the ABS light go out when you get moving? Yes I said, over 5mph once it gets a good signal from each wheel sensor. Right oh, he said and off he went for a drive with the decelerometer sitting in the footwell.

Craig.