I had similar fault. DATAB wire no comms. You have to buss out the wiring between the engine bay fuse box and the interior fuse box (BSI). Look at my thread on airbag fault. I had a break in this wire. Ended up cutting the cable midway, bussing to both connectors, then inserting new wire to bypass open circuit. You may however have a fault on the BSI PCB or the engine bay end. So start with the wiring check.
Seems to be a lot of airbag threads recently ???
Don't buy a new Bsi (body control unit) for your Citroen until you have read this and tried a factory reset first. Very often the reset will solve a multitude of problems especially the ones that suddenly happened after you fitted a new battery to your Citroen or the ones that just 'appeared' form nowhere!
Wipers stopped working?
Central locking gone mad?
Windows stopped working?
Indicators and lights doing their own thing?
All of the above can be caused by a nutty BSi and often a reset is all it needs so try this....
Put the driver's window down, lift the bonnet and ensure all equipment is switched off.
Ensure all doors are closed and remove key from the ignition.
Wait for 3 minutes, disconnect the vehicle battery and wait 15 seconds.
Reconnect the vehicle battery, wait a further 10 seconds (do not open doors.).
Switch on the side lights through the driver's window.
Switch on the ignition and check system's functionality.
Hold lock button on key down for 10 seconds.
Remove key open & close door test central locking system.
Start the engine and complete the system's check.
Failure to follow this procedure could result in incorrect operation of many BSI related items.
Good luck and please let us know if this helped,
Thank you all for your replies.
I have found a broken wire in the engine compartment, just as it enters the fuse box. It's part of the comms that goes around BSI, airbag etc. Reconnected and it's fine now.
That also cleared the DATAB fault, just as Modytop said. No fault lights now :-).
The BSI reset procedure as described by Liliflower, is very handy too and I follow it every time I disconnect the battery.
Many thanks lads.