P1D99 – Incorrect Gear Ratio Clutch ‘B’ Or ‘E’ Defective

P1D99 Possible Symptoms

Engine Light ON (or Service Engine Soon Warning Light)

P1D99 Possible Causes

Faulty Transmission Internal Components

P1D99 Description

The Transmission Control Module (TCM) monitors for conditions which lead to an unexpected transmission gear ratio (e.g. slipping clutches, hydraulic or mechanical defects, etc.). The TCM compares the actual gear ratio (i.e. the ratio of input speed to output speed) to a minimum and maximum calibrated gear ratio value. The TCM performs this comparison while driving in a fixed gear, during gear engagement, and during shifting from one gear to another.