The system covered in the video is very simple but takes away any chance of the engine being cranked over when someone is working in the engine compartment. The interlock push button is adjustable and connects when the rear engine door is closed or if pushed manually.
There are a few problems that arise with this system including the switch itself being out of adjustment or the wiring not connected due to corrosion or poor contact. It’s like any other electrical circuit that is not invincible to the environment or unforseen wear.
Other interlocks that prevent starting is the emergency exits. With the pusher school bus there is the emergency side door exit and the rear emergency window. If they are bolted shut the engine will not crank over. This system is called the “Vandalock” which not only prevents starting but also prevents entry.
The odd time I’ve received radio calls regarding a no start condition while a driver is on a run. There have been instances where the bolt on the side emergency door has been closed accidentally or intentionally since it’s accessible by passengers. A boot to the latch could close it easily preventing start up.
When a driver calls with a no start the first thing I ask is if the emergency exits can be opened. This will determine if the vandalock latches have been closed. The next step is to start the bus from the back / engine compartment. This step eliminates the front end electrical from the operators cab.
If the bus has a shift selector with the handle the bus will not crank over if the transmission is not in neutral. This is a standard interlock just like regular automobiles and of course safety is the main drive for this feature. How many stories have you heard about a vehicle left in gear and someone starts the engine? This is mainly on older vehicles or the neutral start electrical system is faulty.
Checking the neutral start system is part of a motor vehicle inspection and should be part of any check over on a regular service. Every one of our fleet buses have automatic transmissions and most of them are a push button shift pad. New technology has allowed the use of many starter interlocks to safe guard and protect people working around engines. Thanks for reading this post! Comments Welcome.