Maintaining Your Vehicle
Electrical System in Your Car

The Electrical System in Your Car: Common Malfunctions and Maintenance

Updated Jan. 2, 2021

Modern vehicles rely heavily on complex electrical systems. In earlier vehicles, it was only really the lights and starter motor that relied on electrical power. Now, the lights, wipers, windows, doors, airbags, power steering, stereo, instrument panel, anti-lock brakes, engine control unit and most other primary systems in standard road vehicles depend on electricity. The battery, alternator and starter motor are the three main components of your car’s electrical system. It is through these devices that every other electrical feature draws power, via a complex network of circuitry and switches.

Problems with the electrical system can be difficult to diagnose, though are often fixable with something a simple as a replacement fuse or a new light bulb. Beyond these basic remedies, tinkering with your vehicle’s electrics is usually a job for a trained technician.


The battery is arguably the most important component of your vehicle’s electrical system. Without the battery, the engine cannot start and nothing else in the vehicle that depends on electrical power will work. The battery’s two main roles are:

  • Powering the starter motor (which activates the internal combustion engine’s sparkplugs)
  • Running peripheral electrical systems like the lights and stereo, while the engine is turned off

Most batteries last around three to five years before they must be replaced. However, extreme climate conditions can shorten battery life by up to three years. If the battery in your vehicle runs flat (loses all electrical charge) you will not be able to use any electrical systems or get the engine running, without jump-starting the starter motor. This will involve creating a circuit between your flat battery and a charged car battery, using jumper cables.

As the battery is not designed to power auxiliary electrical systems for very long, it will quickly run out of charge if you accidentally leave your lights or some other electrical feature running while the engine is turned off.

Starter motor

When you turn your key in the ignition or press the ignition button, the battery sends a powerful jolt of energy to the starter motor. The starter motor then initiates the compression of air and fuel in the engine cylinders and powers the sparkplugs, which ignite this mixture. This is the starter motor’s only job – but it is an important one. If either the battery or the starter motor fails, the engine will not start.

Powering the engine’s initial fuel compression and ignition takes a great deal of energy but once this task has been carried out, the engine requires no further electrical power to continue running. The computer system which manages engine function and efficiency does require electricity, though this is not produced in the battery.


The electricity needed to power your vehicle’s electrical systems while the engine is running is produced by the alternator. This device uses a belt that is driven by the engine, to convert kinetic energy into electricity. In addition to powering electrical features like lights and wipers, your car’s alternator recharges the depleted battery. This ensures the battery will have enough power to complete the ignition process, the next time you start the engine. The alternator produces an alternating current (AC) which is then converted to a direct current (DC) before it can be stored in the vehicle’s battery.

Contrary to what many drivers believe, the alternator does not run continuously while the engine is on. Instead, it works with the battery to maintain the minimum voltage necessary to keep the car’s electrical systems running, while making sure the battery itself is topped up. Modern vehicle alternators are forced to work extremely hard and as a result, only last for about three or four years, which is a shorter lifespan than the average car battery. Remember that the battery depends on the alternator to recharge. This means that if the alternator fails, the battery and starter motor will not work either. If your battery is dead but does not appear to be corroded and no electrical systems have been left running, the alternator could be to blame.

Electrical systems and circuits

These days, practically every feature and control in a new vehicle relies - in some way - on the car’s electrical system. Some of the most common electrical features in modern vehicles are:

  • Windshield wipers
  • Power windows
  • Power door locks
  • External and internal lights
  • Stereo
  • Navigation system
  • Digital gauges and lights on the instrument panel
  • Power seat adjustment
  • Air conditioning
  • Power steering
  • Anti-lock braking

While none of these systems will prevent the engine from working if they fail, they may still render the vehicle undrivable. For example, you cannot drive at night or in poor visibility conditions without functioning headlights and taillights. If it rains and your windshield wipers are not working, you will not be able to maintain a clear view of the road. An electrical failure that affects your door locks, power steering or anti-locking braking system could be extremely dangerous, particularly if the failure occurs while you are driving the car.

Every electricity-powered feature in your vehicle runs on an electrical circuit. A circuit is essentially a loop of wire which connects the component being powered with the source of power (the alternator or battery), through which electricity can continuously flow while the component is in use. Most vehicle circuits supply power to more than one component. For instance, your windshield wipers and power windows may be part of the same circuit. Thus, if there is a problem with that circuit that disrupts the flow of electricity, both the wipers and power windows will fail.

Your vehicle owner’s manual should contain a circuit map, explaining which electrical systems operate on which circuit. It can be useful to refer to this section of the guide when attempting to diagnose a failure in an electrical component. If that component shares a circuit with another component, which has also failed, you know the problem lies somewhere within the wiring of that circuit. If a component has failed yet all other systems on that circuit are operating just fine, the issue is likely caused by a malfunction in the component itself.

Common circuit malfunctions

If a problem with one of your vehicle’s electrical systems prompts you to book it in for a service, the mechanic or technician working on the car will attempt to diagnose the issue by inspecting the wiring of that system’s circuit. There are four common circuit problems that could divert electricity away from an electrical component, causing it to fail:

  1. 1

    An open.
    There is an opening in the wiring somewhere which has broken the circuit. This could be caused by a broken wire, a loose connector or corrosion around a connection point.

  2. 2

    A short.
    The electrical current continues to flow but is diverted towards the ground, rather than passing through the component. This can occur when a wire rubs against a sharp metal edge in the body of the car and its protective casing is broken.

  3. 3

    An intermittent short.
    A short that comes and goes, as a wire sometimes connects with metal components in the vehicle. This can happen as heat causes vehicle components to expand and contract, or due to the motion of the car causing wires to move.

  4. 4

    An overload.
    An electrical device powered by the circuit is placed under strain, causing it to draw more electricity from the circuit than usual. For instance, the circuit powering the windshield wipers may overload if the wipers are placed under strain while trying to clear heavy snow or ice from the windshield.

Shorts, intermittent shorts and overloads will all cause the fuse on that circuit to blow (or will trip the circuit breaker, in vehicles that do not have fuse boxes). If you replace the fuse and it immediately blows again, you know you have a short circuit. If the circuit has simply been overloaded, the system should work as normal once the cause of the overload has been remedied and a new fuse has been installed.

Fuse boxes

Electrical circuits include a fuse or a circuit breaker to protect the wiring in the event of a short circuit or overload. Fuses contain a delicate metal filament that maintains the circuit but can only handle a certain amperage. If a short or overload causes a power surge that could endanger the entire circuit, the filament will break to open the circuit. The fuses for every electrical circuit in your vehicle can be found in the fuse box.

Most cars have two fuse boxes. One box is usually found in the engine compartment and manages circuits for electronic drive features, like anti-lock brakes. The second box holds fuses for the circuits which supply devices in the passenger compartment, such as the windshield wipers, stereo and power windows. This second fuse box may be in the glove compartment, or under the dashboard on the driver’s side of the vehicle.

Replacing a blown fuse is a quick and easy job that does not necessarily require a mechanic. Refer to your vehicle owner’s manual to find out which fuse relates to which electrical feature, then switch the appropriate fuse out for a new one of the same amperage.

Engine control unit (ECU)

All modern vehicles have an engine control unit (ECU), which may also be referred to as a powertrain control module (PCM) or an engine control module (ECM). The ECU is essentially a computer, connected to various sensors in the engine and fuel system. Using information collected from these sensors, the ECU manages the air-fuel mixture being fed into the engine, the timing of valve openings, ignition sequencing, engine idle speed and various other essential drive functions, to maximize energy efficiency and power.

If the engine control unit malfunctions or fails altogether, your vehicle may be rendered completely undrivable. This is more likely to be the case in newer vehicles, as practically all essential processes in modern cars are dictated by the ECU. It is vital to get your vehicle checked out by a technician immediately if you suspect a problem with its ECU. Any component or function regulated by the ECU is liable to sustain damage unless the system is repaired.

You may have an issue with your car’s engine control unit, if:

  • The car will not start
  • The “check engine” light remains on
  • The engine stalls, misfires or behaves erratically

Malfunctions and failures in a vehicle’s ECU are commonly caused by moisture damage and corrosion because the protective seal around the module has worn out. A defective starter motor sensor could also be the culprit, as this sensor is responsible for directing the right amount of power to the ECU.

Electrical system maintenance

Your vehicle’s electrical system must be checked regularly and kept in good working order. Never ignore minor electrical problems, as they could be a symptom of a larger circuitry issue which will cause serious malfunctions later. An electrical system failure could have catastrophic consequences if it occurred while you are driving the car. Could you maintain control of the vehicle if you suddenly lost the power steering and anti-lock braking systems, while traveling along the roadway at speed? The chances of a collision occurring would be enormous and if that did happen, your air bag would not deploy to protect you.

A problem with the vehicle’s electrical system could result in a wide range of symptoms in all electrical features, and the engine itself. For instance:

  • Your power seat adjustment controls may be less responsive
  • The windows take longer to roll up or down
  • The engine struggles to turn over, or stalls more frequently
  • The “check battery” light on the dashboard has come on
  • The headlights, taillights or turn signals are dimmer than usual
  • You cannot activate your high beam lights

If you notice any of these issues, it is time to get the vehicle’s electrical system health-checked by a mechanic. Vehicle electronics are designed to be resistant to wear, though individual components in the system will not last forever and will eventually need to be replaced.

Overtime, the alternator belt becomes slack and will need to be adjusted to meet the recommended tension in the manufacturer’s handbook. If the belt becomes cracked, worn or damaged in any way, a replacement built will need to be fitted.

Keeping your battery in good working order is an essential electrical system maintenance task. The connections must be kept clean and free from corrosion, especially where the battery cables meet the positive and negative poles. Your vehicle owner’s manual should include instructions and safety guidelines to talk you through cleaning the battery yourself. If you would prefer a less hands-on approach, a mechanic will be able to service the battery for you.

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