Principles of Operation: Gauges: Tachometer
WARNING: This page is about a different car, the 2006 Mercury Grand Marquis and 2006 Ford Crown Victoria. However, it is still accessible from the selected car via links, so may be relevant.
The tachometer is electrically operated and indicates the engine speed in revolutions per minute (rpm). The tachometer range is 0 to 7,000 rpm. The PCM uses the crankshaft position sensor to measure the engine rpm and sends the data to the instrument cluster, over the high speed CAN, to command the tachometer gauge. If the rpm information sent to the instrument cluster is invalid or missing, the instrument cluster defaults the tachometer to 0 rpm.