For 1990-2009 cars

Transmission fluid life is determined by monitoring transmission fluid temperature over a period of time. The transmission control module (TCM) calculates transmission fluid life based on a set of temperature ranges stored in TCM memory. A counter increments as the vehicle is driven. The rate at which the counter increments, depends on the temperature range in which the transmission is currently operating. The higher the temperature range, the faster the counter increments. As the counts increment, the TCM will begin to decrease the fluid life percentage from 100, high fluid life, to 0, low fluid life. When the transmission fluid needs to be changed a DTC P1868 will set and turn on the service vehicle soon (SVS) light. The fluid life percentage can be reset with the scan tool.