The tachometer is directly controlled by the PCM using a pulse width modulator (PWM) signal based on information received from the crankshaft position (CKP) sensor. When the key is ON, the PCM receives battery voltage from the instrument panel cluster, IPC circuit 121, and senses if the circuit contains a fault by using a diagnostic feedback signal. The PCM provides the ground for the tach signal directly.

Important: The tachometer diagnostic feedback signal is continuously checked when the ignition is ON. The tachometer is not controllable by the scan tool.

DTC P1693 will set if there is an open, short to ground, or short to voltage in the tachometer circuit.

Use the scan tool to read engine RPM. If the RPM is correct, circuit 121 or the tachometer is at fault.