Checking Voltage

Overview of Electrical Circuits

• Vehicles use electrical circuits to supply power and ground to various components.

• These circuits typically operate between 50 millivolts (mV) and 15 volts (V).

• If a circuit fails or malfunctions, a digital multimeter (DMM) can be used to diagnose and locate the problem.

Reasons to Check Circuits for Voltage

Circuit Diagnosis

• There are several reasons to troubleshoot a circuit and test voltage.

• Common causes include poor circuit performance, such as:

  • A headlight bulb that appears dimmer than normal.

  • A power window motor that operates slowly or weakly.

Instrument Cluster

• Another reason to check circuits for voltage is to determine if electrical components are functioning properly.

• Examples include instrument cluster lights or headlights that are too bright.

Sensor

• Diagnosing sensor signal issues is another reason to check circuits for voltage.

• Example: a fuel tank pressure sensor code indicating a faulty signal or voltage problem.

Interior Lighting

• Another reason to troubleshoot a circuit and test voltage is when an electrical device is inoperative or malfunctioning.

• Examples include:

  • A radio that doesn’t turn on or function correctly.

  • Interior lights that don’t illuminate when the door is opened.

  • Door chimes that don’t sound, or that stay on after the door is closed.

Checking Fuses

• Lastly, checking if a fuse or other circuit protection device is intact and not blown is another reason to troubleshoot a circuit and test voltage.