ABS Pump
 

having had a warning light and a code for low brake fluid pressure, it was clear the ABS pump had slowly given up the ghost at 212,000. A used/replacement has been procured via A8 Parts. Just some advice. The pump is in 3 pieces, the control module (black), the manifold block (silver) and the pump which is the black cylinder. If I have low pressure I assume it is the pump.
I have 3 options:
1) Split the pump off and replace the pump alone (If I do that does the system need bleeding?)
2) swap in the block and pump and retain my control unit?(in case of any compatibility issues, my replacement is from a 3.7 mine is an S8)This will require a full bleed of the system
3) Swap the lot?
Apart from a low pressure warning light the system was in perfect working order.
Thoughts and advice on a postcard please.
Many Thanks.

I would say swap the lot and make sure it's exactly the same part number.

If it was me I would try replacing the pump and the solenoid pack at first. These two units are connected together with cables so changing one without the other is gonna require some wire work. Not swapping the valve body (the silver part) will avoid the need for bleeding the system and is also less messy. The problem you do have though is that low pressure could actually be a problem in the valve body as this is where the pump is located. The motor simply operates a cam wich pushes on plungers, these create the hydraulic pressure. The pump can be removed without loosing any hydraulic fluid. Access will be problematic though. You will have to be creative.

I believe from some work I did on a D3 version of this that you should always swap the whole unit. this is because the valve block and the control unit are somehow "matching pairs" to eeach other and unless the one youre replacing has the same software and hardwarre part numbers then you wont be able to get them to work without a fault still appearing. As soon as I followed that rule and changed the whole unit, no problems and the error codes went away +++