Not got a Doblo, but in to 500 and Panda it is possible for the brake switch to go faulty but still operate the brake lights correctly - very confusing but strangely Fiat.
Anyway, I'd definitely eliminate any possible electrical issues before touching the actuator. MultiECUScan can correctly read the codes from the gearbox ECU, so I always use it when looking at a Dualogic. I have tried other readers, with varying success, but mostly they either don't read codes at all, or misinterpret them.
The reason I think it must be electrical is that it works in one mode, but not in the other. If the actuator was broken, it shouldn't work in either mode. At least, I've never seen one fail like that.
Anyway, I'd definitely eliminate any possible electrical issues before touching the actuator. MultiECUScan can correctly read the codes from the gearbox ECU, so I always use it when looking at a Dualogic. I have tried other readers, with varying success, but mostly they either don't read codes at all, or misinterpret them.
The reason I think it must be electrical is that it works in one mode, but not in the other. If the actuator was broken, it shouldn't work in either mode. At least, I've never seen one fail like that.