Dispatch ABS wiring/Eolys tank/electrics, any DIY hints?

[sibo]

After spending too long trying to get this sorted on the drive, I'll get booked in with somewhere this week (recommendations on Sheffield Citroen specialists greatly receieved) - but figured a post on here might give me some DIY hints in the meantime.

2016 Citroen Dispatch 1.6 BlueHdi, VF7**************[VIN obfuscated, can be read by forum staff]

I've had ABS/ESP lights on for a good few weeks now, but that's recently been joined by SERVICE and the Orange! EML light. My 2 Autel readers don't work well on this van - the VIN lookup doesn't work and I can't read the codes. If I clear codes using the Autel Maxidiag MD806, the service and EML lights go out, but immediately light back up. Local garage found the same with a larger touchscreen Autel setup, couldn't get any actual codes to show.

I've borrowed a dongle style OBD2 reader, with phone app that initially brought up
U3FFF(FF)
U118 BSI communication failed
P1434(96) EOLYS Function
P1435(00) EOLYS Communication
U1213(81)
P02CF(00) Injector 2 offset learning at max
C003A(01) Rear RH ABS sensor circuit
C003A(11) Rear RH ABS

along with various others that cleared and haven't returned.

I replaced the rear RH ABS sensor, no different. Checked the cabling, which has clearly been previously patched near the exhaust/Eolys under the NS sliding door. Nothing obviously amiss, but with talk of this all rotting I removed the rear of that loom back to the sensors. OS was filthy wet, so I've re-wired that. Reconnected at the previous join/patch point and I now get different codes. Suggests I've cocked up the wiring, but I'm fair confident that my bits are good - multimeter tested for continuity.

I now get
U3FFF(FF)
P1434(96) EOLYS Function
P1435(00) EOLYS Communication
U1213(81)
P02CF(00) Injector 2 offset learning at max
C0037(01) Rear LH ABS sensor circuit
C0037(11) Rear LH ABS
C003A(01) Rear RH ABS sensor circuit
C003A(11) Rear RH ABS

So the BSI fault has gone, but that did set me pondering whether this could all still be wiring related, or even where the ECU gets involved. I've also never had a battery or alternator - do low voltage issues sometimes lead to other issues?

The van drives fine, other than the hill hold not working. One of the handbrake cables was sticking, so I've freed that off while I was under there.

Other possible related history
- Stop/Start hasn't worked in years
- The BSI has previous issues. I've had the bonnet sensor coded out of the alarm and had to wire a completely separate horn after that failed.
- I have had previous work on the Eolys which I think was the pump and a top up. Will be getting copy invoice for that on Tuesday to confirm.

I realise I need someone to have a proper look with a proper scan tool, but I'd also appreciate any pointers on scanners for home use. Also, any suggestions on parts diagrams? I can see used ABS looms, but nothing new. Code looks to be 9819998280