An automotive multimeter is a hand-held meter used to test various components on an automobile. Vehicles of the 21st century rely heavily on electronics to run, which has increased the functionality of the multimeter.
The average consumer grade automotive multimeter is able to check a variety of car functions. The least expensive models check for problems with diodes, batteries, fuses, switches, solenoids, and relays. These are sometimes referred to as "volts-ohms-amps" meters, since these are the three electronic readings that they are able to check for.
There are two basic types of automotive multimeters available. An analog multimeter uses a needle to show readings, while a digital has a screen that gives readings. Either is acceptable for use, although most digital multimeters have a backlit screen which allows for a greater diversity of location when testing. Checking a battery on a dead car by the side of the road at night is probably easier with a backlit automotive multimeter. The analog's ability to measure in real time makes it most helpful when measuring a variable that is changing quickly, as digital readouts have a lag time on them.
For about $50 US Dollars (USD), a consumer can purchase a higher grade consumer automotive multimeter and add in the ability to check additional car functions. Included in the list of additional testing functions should be the ability to measure: duty cycle, pulse width, revolutions per minute (RPM), and temperature. Duty cycle gives the percentage of time that the fuel injector is held open. Pulse width tells exactly how many milliseconds the injector is open for. RPM measurements help in timing the engine, while temperature is relevant to fluids in the vehicle like coolant, transmission fluid, and oil.
A feature that many find helpful when working with an automotive multimeter is called continuity. Wires are considered to have continuity when they are connected or continuous. A multimeter that can check for continuity generally has a buzzer that will go off when the two testers touch. This is especially useful to see if the wires being tested are connected to one another. If the user connects to a wire that does not have continuity, no sound will be produced.
All multimeters have a maximum amp allowance. The least expensive models come with a 10 amp maximum fuse, which means that testing a part with a greater output will blow the multimeter's fuse usually beyond repair. For this reason, most mechanics will suggest finding an automotive multimeter with at least a 20 amp limit.
