Diagnosing Non-Start

[bmwz3tower]

I was doing a motorway drive and stopped at the services, went to start the car, turned the key and it wouldn't start, it wouldn't crank. I tried I few things but it still wouldn't go. So I called the recovery service. They took 2 and a half hours to get there, just before they arrived I turned the key and it started.

I've read up on it and it sounds like it could be the EWS/immobiliser or the starter solenoid. I'm not sure how to diagnose it seen as the issue has disappeared.

I'll try to give some details that might help diagnose it.
My assumption is that it was something to do with driving for an extend period of time as it was the first time I've driven for over 2 hours without shutting off and restarting. I had a cig lighter voltage read plugged it read 12.3v.
When I turned the key ( to turn the ignition on, not to start) the dash lights came on. However, when I turned the key to start the radio screen did not dim- like it does normally when starting. And the engine didn't crank.
Suggesting no power to starter.
I did try disconnecting and reconnecting the battery but didn't change anything.
For what it's worth I don't think I heard the solenoid but I'm not certain.

Any help with diagnosing and preventing this from happening again would be much appreciated.

 

[bonbon]

Starter brushes?

 

[Tomk]

Double check battery terminals. I spent months trying to diagnose a similar problem and it was just a lose nut on the positive terminal.
Maybe cam sensor on the way out? I believe they can cause erratic starting as well as bad running.

hope that’s some help.

oh and stick an obd, see what faults that throws up.