Tach Signal
Range: Active/InactiveThis data indicates whether the BCM is acknowledging a tachometer signal message at the instrument cluster via the SPI serial data line. When the BCM is measuring a tachometer signal message at the instrument cluster via the SPI serial data line, ACTIVE is displayed. When the BCM is not measuring a tachometer signal message at the instrument cluster via the SPI data line, INACTIVE is displayed.
The instrument cluster receives a discrete tachometer signal from the PCM. The instrument cluster calculates the engine RPM based on the tachometer input and drives the tachometer gauge. The instrument cluster also determines if the discrete hardware input is toggling. This input sets a bit in the SPI data return line to the BCM.