So this one is a bit weird. The code we have right now does the following:

 m_pVehicle->SetEngineBroken(bEngineBroken);
 m_pVehicle->SetEngineOn(!bEngineBroken);
 // We need to recreate the vehicle if we're going from broken to unbroken
 if (!bEngineBroken && m_pVehicle->IsEngineBroken())
 {
 ReCreate();
 }

The if is never actually taken, since IsEngineBroken() == bEngineBroken due to previously setting SetEngineBroken(bEngineBroken);. Usually I'd just fix the issue, however after looking into git blame we've had that issue (at least) since the initial open sourcing of MTA back in 2008. As I'm not aware of us having any issues with broken engines, I'd suggest we just remove the unused part of the code.