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Automotive Electronics Fundamentals Explained

Knowledge of electrical fundamentals is essential for proper automotive electronics diagnostics

Importance of Automotive Electrical Fundamentals

Modern vehicles rely on electronics more than ever before. Therefore, it is important to know electrical systems fundamentals. Attempting to diagnose an electrical problem on a vehicle without understanding the basics of electrical circuits can lead to vehicle damage. For example, misdiagnosis of an electrical module’s failure such as an engine control module (ECM) or body control module (BCM) can be a costly mistake as unaddressed the underlying problem can potentially damage the replacement module.

Voltage (Volts)

Voltage is the difference in potential from the negative to the positive side of a circuit.

  • The most common automotive electrical systems use 12-volt circuits which are powered by a lead-acid battery. (While hybrid or electric vehicles operate at higher voltages, this video series is focused on traditional 12-volt automotive electrical systems.)
  • Most automotive sensors use reference voltage, which is a maximum of 4.9 volts and is often referred to as “5-volt reference voltage.”
  • A fully charged automotive battery will read 12.6 volts with the engine off, while alternator charging voltage (engine running) can vary between 13.7 and 14.5 volts.

Amperage (Amps)

Amperage is the measure of movement of charged electrons through a circuit in Amps. This term may also be called “current”.

  • The amperage can vary depending on the type of circuit in the automotive system.
  • Traditional automotive circuits are rated from 5 to 30 amps, depending on the load.
  • Always replace fuses with the same amperage rating as the original. Replacing a fuse with a higher amperage fuse will overload the electrical circuit.

Resistance (Ohms)

Resistance is the opposition to electrical current flow measured in Ohms.

  • Resistance is the working load of the circuit. For an example, in a headlight circuit, the headlight uses the positive electrons from the battery, making it the load of the circuit.
  • Resistance is measured in Ohms using a DVOM (Digital Voltage Ohm Meter). This term is derived from Ohms Law which is used to relate voltage, amperage, and resistance of an electrical circuit.
  • The formulas for Ohms law are:

    V = I x R     I = V/R     R = V/I
    V = Voltage
    I = Amperage
    R = Resistance

  • Everything in an electrical circuit creates resistance – even the wires themselves. Wires that are longer in length create more resistance in a circuit.
  • Worn connections, bad grounds, and corrosion can increase resistance through a circuit.

Watch Video Series to Learn More

This five-video series explains automotive electrical system fundamentals. Watch to help improve your diagnostic skills so you can fix it right the first time.