Tachometer
The instrument cluster receives a discrete tachometer signal from the powertrain control module (PCM). The instrument cluster calculates the engine RPM based on the signal. The instrument cluster then drives the tachometer gauge to a corresponding level in response to the signal. The instrument cluster performs the following functions:
| • | Ensures that the tachometer gauge is at the red line before the fuel cutoff |
| • | Determines if the tachometer is toggling |
The instrument cluster sends a message to the body control module (BCM) through the serial periphral interface (SPI) serial data message for diagnostics.
Speedometer
The speedometer is a road indicator. The vehicle speed sensor (VSS) is a permanent magnet generator which is located on the transaxle. The VSS sends an input to the PCM whenever the transaxle differential carrier turns. The PCM then buffers the VSS signal. The PCM transmits the VSS signal to the following components at 4000 pulses/mile through CKT 817:
| • | The instrument cluster |
| • | The cruise control module |
| • | The radio (uplevel) |
The instrument cluster uses the input in order to indicate the vehicle speed on the speedometer.
Instrument Cluster Indicators
The BCM controls the instrument cluster indicators through the SPI serial data communication bus. Refer to Body Control Module System Check in Body Control System.
