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The sensors for the Tachometer, Engine Oil Pressure, Engine Coolant, Engine Oil
Temperature, Engine Load %, and Manifold Boost gauges are connected to the En-
gine ECU. The Engine ECU converts these sensor inputs into data which it sends to
the Interface Module over the J1708 data bus. For that reason, these gauges are called
J1708 data bus gauges. J1708 data bus gauges and connections are shown in Figure 3-
7.
The axle and transmission temperature sensors, the ammeter, fuel level and pyrome-
ter sensors, and pressure/vacuum inputs are connected directly to the Interface
Module and are referred to as private-bus-driven gauges.
The tachometer is similar in construction to the 2-inch gauges except that it is larger
and is not programmable.
Engine speed data originates at a sensor mounted on the engine. The Engine ECU
receives the data, converts it into rpm data and sends it over the J1708 data bus. The
Interface Module reads the rpm data on the J1708 data bus and converts it into tacho-
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