Tachometer

The tachometer displays engine RPM (speed) anytime the power mode is RUN The engine RPM is calculated by a discrete signal sent to the IPC from the PCM. The engine speed signal is active low, with a pull-up resistor located in the PC and connected to switched battery voltage The signal is a square wave with a 25 to 75 percent duty cycle. Each engine revolution is represented by two input pulses. Engine speed is calculated using the time difference between the two consecutive pulses. Accuracy of the final calculations are +1-25 RPM.