The Application of Multimeters in Automotive Maintenance
The input impedance of analog (pointer) multimeters used in the early days was too low, which had a significant impact on electronic circuits during measurement. When testing resistance with this type of meter, a voltage of 9V is mostly used, so it is easy to damage sensitive electronic components. In recent years, new digital multimeters (DMMs) have been widely adopted.
Its input impedance is high, and its accuracy and safety are superior to analog meters. The voltage during resistance measurement is also low (usually 5V, Fluke is 3.5V), so it will not damage the components of each sensor. But there is also an issue with the number table. It cannot display information on the increase or decrease in measurement readings. During exhaust emission testing and engine analysis, it is found that a pure digital meter cannot provide stable variation values. Fluke overcame the shortcomings of digital meters and replaced them with analog/digital combination meters. It has both the advantages of a digital meter and the advantages of an analog meter for dynamic measurement.
Considerations for fault diagnosis
When searching for faults in the electrical part of a car, the most important thing is the reasoning process of the cause of the fault. This process is very important. This is because you cannot see the internal situation and cannot dismantle a large number of components like mechanical components. By utilizing logic and reasonable steps, problems can be quickly identified. The key tool in this process is the multimeter.
The class nature of signals
The tested signals mainly include voltage, current, and resistance. But the most commonly used is voltage. The issues involved include: Is there voltage present? What is the voltage value? What should be the normal value? What is the voltage drop of the component or connection point? For example, if the input voltage of a relay is 12.8V and the output terminal is 9.2V, the voltage drop is 3.6V. Please note that the joints of the wires should be considered as components and will generate voltage drops. So it may also cause malfunctions.
Diagnosis of faults in automobiles using analog/digital multimeters
According to different systems, electrical faults in cars can be divided into several categories. Please note that the actual fault may occur in one system, while the test phenomenon may occur in another system. The systems covered by this manual mainly include: charging systems; Starting system; Fuel/air system; Ignition system; Body/engine management/cold system.
Most people do not take a car to a repair shop until it cannot start. The driver is the first to see the malfunction. So the biggest challenge is to determine which system is causing the inability to start. Some faults are formed by long-term accumulation, such as repeated electricity, difficulty starting on hot days, etc. Once the system that may cause a malfunction is identified, it can be tested using a Fluke multimeter.
