Andy, Your steering isn't locking. When the engine cuts out you are losing pressure in the power assisted steering. This makes it almost impossible to turn the steering wheel. If your engine isn't running, the power steering isn't working ...
The same is true of your brakes. If the engine isn't running the brake servo (booster, in the USA..) isn't working. There's nothing wrong with your brakes .. it's just that without the engine running your brake pedal is rock solid and impossible to depress..
You need to identify the cause of the cutting-out. There can be many causes .. so .. get somebody to do a diagnostic check for you with an OBD - hand held scanner - to identify any fault.
Fix the cutting out and you have no steering/brake problems
What is possibly happening is when you brake, there is a vacuum leak caused by the power brake system, this reduces the engine rpm, which in turn effects the power steering which makes it feel like the steering is locking up. This can also happen with a vacuum leak anywhere in the engine or things like a faulty idle adjustment control.... Turn the vehicle on, place your foot on the brake, if the idle speed increases dramatically you have a problem. Then put the vehiclein drive with your foot on the brake. If it nearly dies, again, you have an issue. There are many different things on an engine that can create vacuum leaks. EGR Valves, IAC solenoid, PCV valves, the list goes on.... Good luck finding this particular issue!
Answers & Comments
Andy, Your steering isn't locking. When the engine cuts out you are losing pressure in the power assisted steering. This makes it almost impossible to turn the steering wheel. If your engine isn't running, the power steering isn't working ...
The same is true of your brakes. If the engine isn't running the brake servo (booster, in the USA..) isn't working. There's nothing wrong with your brakes .. it's just that without the engine running your brake pedal is rock solid and impossible to depress..
You need to identify the cause of the cutting-out. There can be many causes .. so .. get somebody to do a diagnostic check for you with an OBD - hand held scanner - to identify any fault.
Fix the cutting out and you have no steering/brake problems
What is possibly happening is when you brake, there is a vacuum leak caused by the power brake system, this reduces the engine rpm, which in turn effects the power steering which makes it feel like the steering is locking up. This can also happen with a vacuum leak anywhere in the engine or things like a faulty idle adjustment control.... Turn the vehicle on, place your foot on the brake, if the idle speed increases dramatically you have a problem. Then put the vehiclein drive with your foot on the brake. If it nearly dies, again, you have an issue.
There are many different things on an engine that can create vacuum leaks. EGR Valves, IAC solenoid, PCV valves, the list goes on....
Good luck finding this particular issue!