What Is a DME Relay?by Robert Moore
A digital motor electronics relay is nothing more than two relays built into one case -- it has two coils and two switches. It is used to control the switched-power circuit for the DME module, the fuel injectors and the fuel pump. This particular type of relay is commonly used in vehicles manufactured by Porsche and BMW.
The Two Circuits
Think of the relay as having a left and right side - each consisting of a coil and switch. The left side is for the DME module. One side of the left coil is connected to a constant ground. The coil receives power when you turn on the ignition switch. This closes the DME circuit, which sends battery voltage to the DME module and fuel injectors, as well as the left coil and the switch. As soon as the DME module is powered on it supplies ground to the right coil - closing that circuit and powering the fuel pump. After a few seconds, the DME turns off the relay until you crank the engine.
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