What Is Safe Mode?
Safe mode is the set of parameters that the car will use if it believes there
is a fault with the engine that could cause irrepairable or long term damage.
How Can I Tell If It Is Safe Mode?
If your car suddenly lost power but before that you didn't notice any problems.
If there isn't vast plumes of smoke coming from the exhaust.
If the oil level is OK. If you had all 3 of those, it is almost certainly safe mode.
What Causes Safe Mode?
Generally it is an excess in expected boost pressure entering the engine.
This excess boost from the turbo tends to happen for 4 reasons.
The boost pressure sensor (MAP sensor) is faulty.
The wastegate is seized shut or slightly open.
The wastegate actuator is faulty.
The air line to the wastegate actuator is damaged or off.
Obviously, if the sensor is faulty, it will tell the ECU lies about the boost pressure.
If the wastegate assembly fails in any way it will fail to open to bypass the turbo.
The turbo will continue to spin up, increasing the boost pressure, causing the fault.
How Can I Fix It?
Initially I would suggest disconnecting the battery for 5 minutes (make sure you know your
radio code before doing this), this will turn safe mode off and your car should run normally
again. Drive home with a bit of care, you may find the car might never do it again. If it does
go into safe mode again, you know you have a real problem and not just a glitch.
Wait for the car to cool down and see if the wastegate arm moves freely.
Use the search function of the site for "wastegate service" to see how
you can possibly free up the wastegate assembly which could be seized.
Check the pipe work to and from everything to rule out leaks.
Try and borrow a MAP sensor to test.
As a last resort, book in with a smart specialist who will diagnose the problem.