1997 Ford Aerostar Owner's Manual - Page 169

The PCM will automatically adjust transmission operation to make up for varying conditions. Several sensors located on the engine and transmission such as throttle position, engine speed, vehicle speed and transmission temperature are used by the PCM to shift the transmission into a higher or lower gear when required for the best performance and fuel economy. For example, you may notice that the transmission will upshift to a higher gear more quickly when the vehicle has not reached normal operating temperature. The PCM also controls the transmission's Torque Converter Clutch (TCC) to further raise vehicle performance and fuel economy. The TCC will engage when the transmission operating temperature and other conditions determined by the PCM have been met. Engagement of the clutch may be noted as a decrease in engine speed. To help in troubleshooting, the PCM continually performs self-tests on the electronic control system and, if any faults are detected, stores them in memory. The Transmission Control Indicator Light (TCIL) (O/D OFF), which is located on the gearshift lever, may flash steadily if a malfunction has been detected. If the TCIL is flashing, contact your Ford dealer as soon as possible. If this condition persists, damage to the transmission could occur. Speed limiter All models are equipped with a Powertrain Control Module (PCM) which limits the maximum engine speed and thus road speed in top gear. Vehicle operation is normal since the controlled maximum speed is above posted highway speeds in North America. 169