The UCH / Body system control unit / BSI controls the immobiliser + it has many other functions like, central locking, hazards, windscreen wipers + many more.
The UCH control unit suffers from general failure or very common water damage.
Remove the plastic cover from round the steering column.
Look to the right-hand side of the steering column, you will see the control box as shown above.
The UCH control unit has 2 plugs 1 x white 1 x black
The UCH control unit can get very dirty and damp, remove the UCH control unit and open it up.
Look at the circuit board, if you see any damp / corrosion this is the problem, some times just the black connector may just be suffering from a dry joint, un-plugging and re-pugging in the black connector can re seat the connections.
PLEASE don’t use WD40 use a brake cleaner or a proper electrical spray.
If the UCH unit is corroded this will need replacing, a replacement UCH unit is about £130, PLEASE order the part from a Renault dealer as they are cheaper than a Vauxhall dealer, the part is a Renault part, the UCH needs programming, we can carry out the programming, we need the original UCH unit and a replacement, we do not supply replacement units as they are only obtainable brand new from a main dealer, we can use second-hand units, we copy the data information from the original unit to a replacement unit so it is a 1 to 1 copy / clone so the replacement unit will be ready to fit.
CAN (central area network)
The UCH is the main CAN control see https://www.csselectronics.com/pages/can-bus-simple-intro-tutorial
If your Vauxhall Vivaro red LED immobiliser light is on solid / not flashing / staying on constantly the CAN has a fault so the immobiliser is fine it works BUT it has lost a connection with the electrical CAN system on your Vivaro, this cannot be repaired by the bypass as the fault is usually a corroded / broken wire.