Beat the Book Automotive electrical diagnosis. Better diagnosis, faster repair. Application Note Work safely This application note is intended as a guide for the professional mechanic. It describes some of the test procedures commonly used by experienced technicians. However, some of the procedures require you to take certain pre- cautions to avoid personal injury and/or damage to equipment or vehicles. Fluke cannot anticipate all possible precautions that you must take on all the different vehicles for which this guide is applicable. For this reason, you should thoroughly familiarize yourself with proper safety habits and take all precautions described in the vehicles repair manuals to avoid injury or damage. Testing automotive systems with an analog/digital multimeter Perhaps the most important tool youll use in troubleshooting auto electrical systems is the multime- ter. The basic multimeter measures voltage, current and resistance, while more elaborate multimeters, such as the new Fluke 88-V, have features that can check things such as frequency, duty cycle, pulse width, make diode tests, and even measure temperature. Although automotive multime- The common analog type mul- In this application note you timeter is not only inadequate, it ters with various capabilities will find troubleshooting tech- have been around for years, can damage delicate computer niques using the high quality, circuitry. Both analog meters and many of them didnt have the affordable and popular line of scales and functions required for test lights, due to their low inter- Fluke analog/digital multimeters nal resistance (input impedance), todays automotive applications. and automotive troubleshooting Hybrid, electric and fuel cell draw too much power from the accessories. Flukes analog/ device theyre testing to be used powered vehicles have special digital combination has distinct requirements, ones met with the on computers. Whats more, advantages over either digital many analog meters use 9V to new 88-V. Now that computers or analog meters alone, and and their sensors are a part of power the resistance test, which the accessories are designed to is enough to destroy sensitive everyday automobile trou- make your job easier and more bleshooting, you need a true digital components. profitable. multimeter to do the job. From the Fluke Digital Library www.fluke.com/library Over the last couple decades, a The presence of voltage tells you Thinking about different type of multimeter has that the circuit is delivering elec- troubleshooting evolved to solve problems not tricity to the component youre When troubleshooting electrical addressed by analog multimeters. testing. systems, its important to use a Digital multimeters (DMMs) have The voltage reading tells you logical process of deductive much higher input impedance whether the proper voltage is reasoning to solve the problem. than analog meters, generally arriving at the component. This process is most important 1 Meg ohms (million ohms) to By measuring available voltage since you cant see inside or dis- 10 Meg ohms. The high imped- at a component, you can deter- mantle the majority of electrical ance means that the meter will mine whether the voltage components to tell whether draw very little power from the reaching the device is adequate. theyre functioning, as you can component under test. Besides The voltage drop across a with mechanical devices. providing more accurate meas- component tells you how much of Jumping to conclusions can be urements, this type of meter will the voltage is being consumed by expensive and time consuming. not damage sensitive computers. that component. With well thought-out and The one problem with digital For example, if a relay has organized steps, you can usually readouts has been that the num- 12.8 volts on the input side and determine the source of the prob- bers displayed didnt give much only 9.2 volts on the output side, lem the first time. information about whether the the voltage drop is said to be 3.6 The key tool in this process is reading was increasing or volts. Remember that wire and the DMM. decreasing. You may have experi- connections can also be consid- enced the frustration of trying to ered components and may cause Types of measurements read the constantly changing voltage drops if faulty. numbers on digital exhaust gas When troubleshooting auto-elec- analyzers or scan tools. trical systems, you measure Fluke has overcome the prob- voltage, current and resistance. lems associated with traditional Probably the easiest and most analog and digital meters by useful measurement is voltage. It providing a combination display can answer these questions: that gives you the accuracy of a Is voltage present digital readout with the dynamic What is the voltage reading measurement capabilities of an analog meter. Rather than adding What is the available voltage new meters to test every gizmo What is the voltage drop that comes along, one good across a component or multimeter will suffice. connector The Fluke 88-V Analog/Digital Automatic Polarity and Range Multimeter has several features Selection The meter automati- that make it well suited for cally selects the range and automotive troubleshooters: polarity for the best possible reading. Analog/Digital Display Combined 33-segment analog Continuity Beeper Audible bar graph and 6000-count digital beep tone provides easy testing display. for continuity, shorts and diode tests. Peak Min/Max The Peak Min/Max function stores the low- Rugged Construction Tough est and highest measurements plastic case survives the made by the meter as fast as everyday hazards of working 250 S. in a shop. Meter is backed by a limited lifetime warranty. Auto Hold The meter display freezes a reading until youre ready to look at it. 2 Fluke Corporation Beat the book