A number of tools make diagnostics easier. They allow you to measure electrical activity on circuits and components that would otherwise be undetectable.
Digital Volt-Ohmmeter (DVOM)
A 10-megaohm digital volt-ohmmeter (DVOM) or multimeter, such as essential tool J-39200 (Fluke 87) or equivalent, is useful for testing different aspects of circuit operation. The Fluke 87 Digital Multimeter (figure 6-2) is an example of a digital multimeter.
The digital multimeter has an electronic digital readout of the value measurement being made. This type of meter has electronic circuitry for precise measurements. It is accurate to within .1 percent.
A multimeter with at least 10 megaohms input impedance is needed for use on GM vehicles. This input impedance applies to the meter only when it is used on the voltage scale. This means that the meter resists loading down the circuit being measured with a resistance of 10 million ohms. This high resistance permits measurement of very sensitive circuits without damaging or altering them.
The DVOM can function as a voltmeter to measure the magnitude of voltage. When used as an ammeter, the DVOM accurately measures extremely low current flow. When used as an ohmmeter, the DVOM measures the resistance of a circuit in ohms. These uses are described on the following pages.
