Gauge Indication Systems: Tachometer
WARNING: This page is about a different car, the 2003 Mazda Tribute. However, it is still accessible from the selected car via links, so may be relevant.
The tachometer is electrically operated and indicates engine speed in a range of 0 to 8,000 rpm. The tachometer receives the signal via the SCP (J1850) line from the PCM. If the rpm information sent to the instrument cluster is invalid or missing the instrument cluster will default the tachometer to 0.0 rpm.