2008 BMW Z4 2.5 – Recurring immobiliser/CAS fault, advice needed

[DianaKyte1]

Hi everyone, I'm looking for advice on an ongoing starting problem with my 2008 BMW Z4 2.5 petrol.

Over the last four months, the car has intermittently refused to start. When I turn the key, the dashboard lights and radio come on normally, but absolutely nothing happens — no clicking or engine turning over. Both keys have now had the same problem.

A mobile auto locksmith has been out several times:

• Initially, he replaced the original key and its battery.
• When the problem returned, he reprogrammed the immobiliser. The car then worked perfectly for around two months.
• Unfortunately, the same fault returned again.

The locksmith suspected the control unit was somehow losing its programming. Most recently, he removed the CAS unit and inspected/reworked the solder joints, as he said these can suffer from poor soldering and damp. The car is now running again, although he mentioned that the remote is a little sluggish. This repair cost £120.
I've also noticed a yellow battery-shaped warning light appearing for around 20 seconds on morning starts before disappearing. I tried a jump-start pack when the car wouldn't start, but it made no difference.

I'm hoping the CAS repair has solved it, but I'm worried the fault will return again.
My questions:

1. Has anyone experienced similar intermittent no-start problems caused by the CAS unit or its solder joints?
2. Is there anything else worth checking, such as the CAS wiring, key reader or power supply?

Is permanently deleting or bypassing
the immobiliser possible on a 2008 Z4 2.5, and would it be advisable, or is properly repairing the original system the better long-term solution?

1. Could the yellow battery warning light be related, or is that likely to be a separate issue?

I'd really appreciate any advice or experiences from anyone who has dealt with this fault. Thanks!