Jock85 said:

Slight update - I've since replaced the ABS ECU too with a known good one but no change either. Given I've changed the accumulator (new), pressure switch (new), ECU, reset brake plunger, short circuited the brake fluid level sensor connection, soldered the connections at A-pillar, and bled the system per Rave, the only part left to do is replace the actual brake pump itself. As I've replaced the bits listed already, is it even possible for a low pressure signal to come from the brake pump if its duff?
Any help would be MASSIVELY appreciated!

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Jock85 said:

I've just done the test and it's taken 35 seconds to re-pressurise so it certainly looks like it's in the suspect zone. At least that gives me a reason to believe I should replace the pump itself now. I didnt know there was a rave procedure to check the pump against so i'll check that out too. I'll see if I can get a new unit sourced and fit in the next week and I'll let you all know.

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Slow down a bit, yes your pump maybe weak but still builds pressure and shuts down does it not? Your level sensor shows issues, ok with engine off so why not with engine running?
You say "new" pressure switch? your diagnostics shows that 1 side of the switch is bad, that would be where I would be looking not the pump (yet)

Have you actually tested the switch at the switch? The posts from @pwood999 give enough for you to do this.

I would still need to have a good look to understand the (6) in the pressure switch which may indicate the pump is weak?.

Sit down with a cuppa.

J

Jock85 said:

I've just done the test and it's taken 35 seconds to re-pressurise so it certainly looks like it's in the suspect zone. At least that gives me a reason to believe I should replace the pump itself now. I didnt know there was a rave procedure to check the pump against so i'll check that out too. I'll see if I can get a new unit sourced and fit in the next week and I'll let you all know.

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OK, mine. 20 pushes on the pedal with engine off. Key on and it took 38 seconds, also including the drain from the glow plugs cycling.

35 Seconds from zero pressure is about right IMO

Datatek said:

35 Seconds from zero pressure is about right IMO

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Still in the game

marjon said:

Slow down a bit, yes your pump maybe weak but still builds pressure and shuts down does it not? Your level sensor shows issues, ok with engine off so why not with engine running?
You say "new" pressure switch? your diagnostics shows that 1 side of the switch is bad, that would be where I would be looking not the pump (yet)

Have you actually tested the switch at the switch? The posts from @pwood999 give enough for you to do this.

I would still need to have a good look to understand the (6) in the pressure switch which may indicate the pump is weak?.

Sit down with a cuppa.

J

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Thanks gents - appreciate the involvement and testing of your own equipment. Yes, you're correct - it does build pressure then shuts off, restarting every 3rd or so press of the peddle so I guess it behaves as if it's reaching the desired pressure.

So following your advice, I've studied the diagram @pwood999 posted. Bear in mind I am not very practiced with electrical diagrams, can I just think out loud here?



Assuming the switch is working correctly:

Contact [4] is normally open/off. The Black/Purple (BP) wire should have 12v which, with a correctly operating brake fluid level sensor, would supply 12v to the BG wire that goes to both the ABS ECU and via Pin 3 into contact [4] of the ABS switch.

Contact [5] gets 12v supply from BW wire via Pin 4 and is mechanically connected to contact [4]. When the system is <110 bar, contact [4] won’t close and therefore BG won’t earth and will register 0 volts. If it is > 110 bar, [4] will close and BG will earth and [5] would open causing BW to be 0 volts.

I’m not sure I completely understand contact [6] but the BY wire feeding it at Pin 2 will close and earth at 180 bar and open below 140 bar causing BY to be 0volts

Therefore a correctly operating switch should behave something like this:

Below 110 bar – BG won’t earth (0v), BW will earth (12v), BY won’t earth (0v)

Over 110 bar – BG will earth, BW won’t earth, BY won’t earth until 180 bar then it should.

So all of this is to say, in order for the ABS ECU (or whatever causes the low pressure warning) to believe the system does not have a low pressure, BG should be 12v, BW would be 0v, BY hopefully 12v if its gets up to 180 bar.

Have I deduced correctly?

Very brief update on this one.
I have FINALLY managed to get the three amigos to extinguish albeit temporarily with something of a workaround.
If I earth the black/green wire (between the ABS ECU and the brake fluid level sensor) at the connector on the brake fluid reservoir the system no longer reads low pressure and the warning lights go out. The car now thinks it has low brake fluid but the actual ABS and pump continues to work as it should and at least I can think about taking it for an MOT and getting it road worthy while I work out a proper fix.
It's not sorted by any means but it just means I'm not ready to kill her off yet!

Does the fluid level sensor actually work as it should?

Mark Piercy said:

Does the fluid level sensor actually work as it should?

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I'm not sure now although it does remain on the suspect list. Definitely an issue somewhere on that circuit though - just glad to make some progress.

Jock85 said:

I'm not sure now although it does remain on the suspect list. Definitely an issue somewhere on that circuit though - just glad to make some progress.

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Fair comment