10/13/2024
Diagnostic Wisdom—
Customer states: “all windows inoperative.”
Where do you start?
Check the fuses and relays first.
What’s a fuse? A fuse is a protective device that protects sensitive modules from excessive current. As soon as a power surge occurs, whether it’s a short or a load that is pulling more amperage due to mechanical resistance in a motor, the fuse/ filament will burn out to prevent further damage to computers or sensitive modules and the circuit as a whole.
What is a relay?
A relay is a device that converts small electrical signals to larger ones and vice versa. In a relay, there is a coil of copper wire that activates a magnetic field and a switch contact. The magnetic field with attracts the switch to power on (normally open) or to cut power (normally closed relay). Now relays also have the same purpose as a fuse; it has to protect the circuit from power surges too. Now when a relay goes out, generally this means that it failed to disperse of any heat that was produced, thus causing a higher resistance than normal and causing the insulation to lose stability. Overloading: this can also cause excessive heat, thus causing what I mentioned previously. Contamination: overtime, contacts may corode, dirt, dust or chemicals may also contaminate the relay causing it to perform poorly or if at all.
Voltage spikes/surges: often caused by hot-switching inductive loads, this will increase wear on the relay. Mechanical wear/ normal wear and tear. General pirpose and power relays generally have a minimum life expectancy of 100,000—1,000,000 uses. Mechanical relays last between 10,000,000—100,000,000 uses. As mentioned, life expectancy varies.
What can cause a fuse to go bad?
Overloading a circuit. Generally in a vehicle, overloading is really only caused by a load pulling excessive amperage (usually a fualty motor with high mechanical resistance).
A short: a short is when current travels through an unintended path. Instead of passing through the load first, it goes straight from the source and back to ground. If you know Ohm’s law, you should be familiar that current will take the path of least resistance. A short is usually caused when a hot wire rubs onto an exposed ground wire or if the wire is rubbing on chassis ground. Ground wires are mounted directly onto metal. The B- terminal is mounted onto the frame. Faulty wires: usually results in a short.
Power surges, as mentioned earlier can also cause a fuse to blow.
Now we know what these devices do, we can easily rule out other issues and look at our list of suspected problems.
If the fuse is what wwnt out. I will utilize a new fuse, rated the same amperage as the old one and test the window motors. Before we do that, we need to check to make sure all power windows utilize the same fuse & relay. If they do, great, if not, determine which window(s) utilize the fuse/ relay that was faulty. Test the motors. If they are working harder than they should (i.e. they are pulling excessive current), that was the culprit. If that wasn’t the case, inspect all connectors a wires that are part of that circuit. Make sure the hot wires aren’t making immediate contact with the ground wire(s). Also check for moisture. This can indicate tyat the door panel seal is allowing the wires to be exposed to water, which can also short out the circuit.
