The main function of a Volvo S40 alternator is to generate the electricity that is necessary to recharge the battery. It is used to keep battery storage charge and to assist in running all electrical accessories including even the ignition and engine control systems. Over time, though, there are a number of problems you may encounter with it. Here is a short list of the problems and symptoms and the simple ways on how to identify them:
Pop up the hood and check the alternator. It is a round, metal engine component, which is rotated by an engine drive belt. When any of the wires are not properly connected, it can reduce or even stop the flow of electricity. An occasional symptom would be brighter lights, since the alternator works itself in producing more energy to counter the resistance from the bad wires or broken connections.
Sometimes, when the key is turned and the car won't start, the immediate conclusion a car owner will have is a dead battery. But it can actually be the alternator that is causing the battery failure. To diagnose correctly, you simply have to jumpstart the car and then take the cables off right away. If the car dies again soon, it is the alternator that has failed. If the car continues to run, though, then the battery has reached its final destination.
If a pulley that is supposed to turn the alternator is not properly aligned or is not turning freely, it will cause more friction on the belt. This creates a lot of heat and result in the smell of burning rubber. This is because of the high resistance caused by faulty, loose, or disconnected wires that push the alternator to produce more power because of the high resistance.
Test the Volvo S40 alternator's power using a voltmeter while the engine is off. Connect the red and black leads to the red and black battery terminals. Then, crack up the engine and check the voltage reading. If the reading is anywhere below the 13.6-to-14.3-volt range, the alternator is definitely failing.