Test and Diagnostic Equipment for Automotive Electrical Systems

Frequently Asked Questions About Automotive Electrical Systems and Vehicle Diagnostics

Electrical faults in a vehicle can have various causes—ranging from a dead battery to damaged wiring and ground connections, to problems with electrical components or connectors. The following questions provide an overview of important testing procedures and the appropriate test equipment.

• What test equipment is needed to diagnose automotive electrical systems?

  That depends on the specific diagnostic task. Typical workshop equipment includes, among other things, automotive test lamps and multifunction testers, multimeters and current clamps, testers for battery and charging systems, as well as devices for testing wiring and voltage.
  
  For special applications, electronic protection devices, voltage maintainers, glow plug testers, and trailer and towing vehicle testers are also available.

• What electrical parameters are measured during automotive diagnostics?

  The most important measured quantities include voltage in volts, current in amperes, and resistance in ohms.
  
  In addition, depending on the diagnostic task, it is possible to perform continuity tests as well as measurements of frequency, duty cycle, or capacitance, for example.
  
  The specific measured quantity required depends on the particular fault pattern and the test equipment being used.

• What is the difference between an automotive test lamp and a multimeter?

  Automotive test lamps and multifunction testers are particularly well-suited for quick functional and power supply checks on appropriate vehicle circuits.
  
  A multimeter, on the other hand, provides specific measurement values for voltage, current, or resistance, for example.
  
  The appropriate measurement method depends on the circuit and the fault being investigated.

• Can a test lamp be used on control units and signal lines?

  Not every test device is suitable for sensitive electronic circuits.
  
  Particular care must be taken with control unit, sensor, and signal lines to ensure that the measuring device used is approved for the specific application. Unsuitable test devices can place excessive strain on the circuit or damage electronic components.
  
  Therefore, the specifications provided by the test device and vehicle manufacturers must be followed.

• How are the vehicle battery, alternator, and charging system tested?

  Measuring the voltage can provide an initial indication of the condition of the vehicle’s electrical system. For a more comprehensive assessment, specialized test equipment for battery and charging systems can be used.
  
  Depending on the test equipment, it is possible, for example, to check the battery’s condition, state of charge, internal resistance, and starting capability, as well as the function of the alternator and starter motor.
  
  Therefore, the battery’s open-circuit voltage alone is not always sufficient to reliably assess the battery’s actual condition.

• How can the current consumption of an electrical load be measured?

  Depending on the application, current can be measured directly with a suitable multimeter or using a current clamp.
  
  A current clamp has the advantage that the circuit does not need to be disconnected for the measurement. When doing so, the measurement range, type of current, and technical specifications of the device being used must be taken into account.

• How do you find a broken wire or a poor ground connection?

  For voltage-free circuits, continuity and resistance measurements can be used for troubleshooting.
  
  However, a circuit may still have electrical continuity when unloaded but still exhibit excessive contact resistance under load.
  
  In such cases, measuring the voltage drop under load can help identify issues such as corroded contacts, damaged wires, or poor ground connections.

• How do you find a short circuit in a vehicle?

  The procedure depends on the specific circuit and the nature of the fault.
  
  To narrow down the problem, you can use, for example, fuse tests, voltage and current measurements, resistance tests on de-energized circuits, and appropriate wire and voltage testers.
  
  Before taking any measurements, consult the wiring diagram to determine which loads and wires belong to the affected circuit.

• When is an electronic or surge protection device used?

  Certain workshop tasks can cause voltage spikes that may damage sensitive vehicle electronics.
  
  Electronic protection devices or surge protectors are used to shield electronic components from such voltage spikes, for example, during certain welding operations or when charging the vehicle battery.
  
  The protection device used must be compatible with the vehicle’s onboard voltage.

• Why is it important to maintain voltage when replacing a battery?

  When disconnecting the vehicle battery, stored settings, learned values, or codes may be lost, depending on the vehicle.
  
  A voltage maintenance system therefore continues to supply electrical power to the vehicle’s electrical system during certain maintenance or repair work.
  
  However, it must not be used if the vehicle or the relevant electrical circuit must be completely de-energized according to the manufacturer’s specifications.

• What should be kept in mind with 12-V and 24-V vehicle electrical systems?

  Passenger cars and light commercial vehicles are predominantly equipped with 12-V electrical systems. Trucks, buses, and other heavy-duty vehicles often use 24-V electrical systems.
  
  Test, measurement, and protective devices may only be used within the voltage range specified by the manufacturer.
  
  A device designed exclusively for 12 V must therefore not be used automatically on a 24-V electrical system.

• How are glow plugs tested electrically?

  Glow plugs can be tested based on their electrical properties or current behavior.
  
  Special glow plug testers are available for quick workshop testing.
  
  This electrical test should be distinguished from mechanical glow plug tools used to unscrew or pull out stuck glow plugs.

• What is the difference between a trailer tester and a towing vehicle tester?

  A trailer tester checks the trailer's electrical and lighting functions.
  
  A towing vehicle tester, on the other hand, checks the trailer's power outlet or the output signals from the towing vehicle.
  
  By testing them separately, it is possible to determine whether a lighting malfunction is caused by the trailer, the connector, or the towing vehicle.

• Can a multimeter be used for CAN bus diagnostics?

  Using a suitable multimeter, certain basic electrical measurements can be performed on the CAN bus.
  
  However, a complete CAN bus diagnosis is not possible with this method alone. Additional diagnostic tools or a suitable oscilloscope may be required to evaluate complex signal waveforms or communication errors.

• Can testers designed for standard automotive electrical systems also be used on high-voltage systems?

  Not automatically.
  
  Work on high-voltage systems in electric and hybrid vehicles places special demands on measuring instruments, test leads, personal protective equipment, qualifications, and work procedures.
  
  Therefore, it must be explicitly verified whether the respective test equipment is approved or suitable for the relevant high-voltage application. Test and safety equipment for high-voltage applications can be found separately in the Electrical Safety section under Alternative Drives / E-Mobility.