School Bus Module Corrosion

Modules have been part of the mechanical world for many years. The technology has advanced in leaps and bounds with more monitoring and control of multiple circuits reducing wiring, switches and connections. Most school bus modules are sealed from the environment however if moisture and oxygen are allowed to enter it’s inevitable a failure will occur.

The video shows a vehicle interface module from a Thomas pusher school bus that’s mounted behind the steering axle. One of the jobs of this module is communication to the engine ECU when the transmission is in neutral to activate the high idle, exhaust brake and neutral start modes. The VIM in the video was causing relays to click intermittently because of the cross talking voltage created by the corrosion.

We’ve had several of these VIMs fail through the years because of an opening in the housing that I’m suggesting was designed that way to cool the internal grid. This module sits in a metal box mounted under the floor boards below the driver. Also enclosed in the box is the transmission control unit. I have never seen a TCU fail because it’s well sealed preventing corrosion from entering.

In a perfect world if every module in the world was mounted inside a vehicle there would be less problems. Of course manufacturers can’t do this for lack of space. With multiplexing incorporated into the trucking industry clean connections and grounds is essential. Any kind of resistance will cause big problems with components and proper operation of the electrical system.

We found a great product called PenLube that we use to spray electrical connections with. Even though the plug-in connectors have a silicone environmental seal moisture still gets inside so spraying this product liberally will disperse moisture and create a nice tight seal.

The last trade show I attended the PenLube representative was there and he put on a demonstration that knocked everybody’s socks off. He sprayed PenLube all over a trouble light top to bottom and took the light with his bare hand and dipped it in a bucket of water while it was plugged in and turned on. That’s what I call a perfect seal between an electrical component and moisture.

The preventive maintenance of an electrical system in my mind is to visually inspect your vehicle electrical system on a regular basis. It isn’t difficult work but you have to be proactive and keep it up because once it takes hold trouble will follow and eventually a major break down will hit you unexpectedly.