Most folks have never heard of transient current flow. It can cause thousands in damage to a vehicles, with very few outward signs. Fortunately it can also be prevented, with a few simple steps.

When the battery powers the accessories, the flow is called current and is expressed in amps. A positive wire runs to the accessory and returns to negative through a ground. The ground is sometimes a wire and sometimes the vehicle body, which is electrically attached to the negative terminal.

The number of amps leaving and returning to the battery has to be equal.

As long as the cables, grounds and terminals work as designed, this is not a problem. When the key is turned, electricity flows from the battery, through a solenoid and to the starter. A solenoid is used, because the key switch cannot conduct the high amperage needed to start the vehicle.  (please click images for a closer view)

After flowing through the starter, the current travels through the engine block, to a heavy cable attached to the negative battery terminal. This completes the circuit.  Both cables flow 275 amps and current returning to the battery equals that leaving it.

Problems occur when corrosion and loose connections cause high resistance. The ground cable may only be able to flow 250 amps. If the starter pulls 275 amps, twenty five amps will find another path to the negative terminal. This is known as transient current flow; electricity taking a path, other than that designed, to return to the battery.  The end result can be considerable damage to seemingly unrelated components.

Because the engine attaches to the body using rubber mounts, it is only electrically connected through the ground cable(s).  If the cable does not conduct well enough, another path will be found. Instead, the additional current flows through the flywheel, transmission, drive axle, knuckles and back through the tie rods. Here is finds a body ground in the steering gear.

Transient current can be measured by placing an amp meter between the starter case and the battery ground.

Transmission and suspension components are not designed to flow electricity. As the current flows through them, metal can be transferred from on part to another. This is similar to the electroplating process. In time the parts are destroyed and there may be a major failure.

Keeping all battery terminals clean, tight and with proper connections can help prevent transient current flow.

Battery terminal corrosion is a symptom of another problem.

Simply cleaning the corrosion away, will only give temporary results. Terminals corrode because acid and gasses leak around their base. This is a defect in a battery and should be covered under warranty. Replacement of the battery and repair of the terminals will solve the problem.

Inspecting the battery and terminals regularly and replacing batteries that leak may save a transmission or suspension rebuild.

A few symptoms of transient current flow

• Premature transmission failure
• Early or repeat tie rod failure
• Early or repeat wheel bearing failure
• Early or repeat rack and pinion failure
• Flickering or pulsing headlamps
• Erratic dash volt meter
• Unexplained or repeat electrical failures

Of course AGCO can diagnose and correct transient current problems or any electrical problems on your vehicle.  Call AGCO, it's the place to go.