Tachometer Inaccurate

CIRCUIT DESCRIPTION
The IPC monitors the tachometer sent by the PCM through CKT 121 (WHT). The IPC software controls one of the following two display types:
^ A message display with a digital IPC
^ An analog gauge with an analog IPC, consisting of a needle pointer

The IPC interpolates and scales the tachometer information received from the PCM.

DIAGNOSTIC AIDS
^ Connect a scan tool to the DLC.
^ Test for any set DTCs if no DTCs are set current.
^ Test CKT 121 (WHT) for an open or short.