'Brake Assist Inop' message

[kiwiCSi]

Have this message appearing on the MID at startup, then goes away if I shut down and re-start the engine.

Troubleshooting has revealed evidence of internal leakage at the Brake Pressure Regulator Pressure Switch and Sensor.

I have both new switch and sensor to install, but was wondering what procedure will avoid (a) fluid spraying out when removing them, and (b) the need for system bleeding afterwards (can't find a procedure in the online shop manual that is specific to just replacing these parts, and previous posts on the subject don't really provide anything conclusive).

My plan is to pump the brake pedal 20 times to remove pressure from the bomb, then hold the brake pedal depressed with a suitable fixture, before removing and replacing the pressure switch & sensor.

Will this action (a) prevent me from getting sprayed with 'Pentosin' during removal of switch/sensor and (b) mitigate any requirement for brake/steering system bleeding after parts replacement?

[tendril]

Pump the brake pedal 20 times to be safe then just replace sensor. No need to keep pedal held. I suspect hardly anything will leak out and it will self bleed later.

(Someone can correct me if wrong! Been a while since I replaced mine)

[kiwiCSi]

OK, thanks for that advice - I'd previously read posts from others who got sprayed with Pentosin upon removing the pressure switches, so just wanted to avoid this scenario, and also prevent fluid from getting on the paintwork.
My idea of keeping the brake pedal depressed is to (hopefully) prevent any air from entering the system through the open switch/sensor ports in the pressure regulating valve, thereby removing the need for post-bleeding.
However I'm unsure if this is entirely effective, or if required at all due to system self-bleeding properties.
I plan to replace the parts this weekend so will report back the results.
Cheers!

[dragon850]

Brake bomb could be toast too

[kiwiCSi]

Brake bomb could be toast too

It was last replaced in 2009, so I guess it's a candidate, but hopefully just the leaking pressure switch and/or sensor are the culprits here.

[kiwiCSi]

Well, I didn't get to the car at all this weekend - had another car to sort out and various other things going on - so will hopefully get these pressure switches replaced next weekend.

[kiwiCSi]

Just a follow-up post, to close off this issue.
I replaced the two brake system pressure switches over the weekend.
No more annoying "Brake Assist" warning message!
Here's a couple of pix of the old removed items, which I believe may have been the original parts from factory.
The upper differential pressure switch (coarse thread) was wet and sticky from an internal 'Pentosin' leak, while the (lower) oil pressure switch (fine thread) was badly corroded.
I'd recommend replacing these parts as an age-related preventative maintenance item, regardless of whether you're getting the warning message or not. I fitted new 'Ate' parts.

[TedBobo]

Thanks for the update! Something else to add to my list.