Mazda3 Engine braking causes limp mode

I have a Mazda 3. Whenever going down a steep hill without using the throttle, or indeed just taking my foot off the gas when travelling at anything over 50 mph, in other words using engine braking, the engine management light comes on and the car goes into limp mode. Restarting the car removes limp mode but the eml stays on. My local garage can’t find the problem - had anyone else had this issue?
 
What's an Engine Management Light? Is that the Check Engine Light, or CEL?

What codes is it throwing?
 
Back