Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Transmission Control (TC) Switch (MKZ)
The Transmission Control (TC) switch is a momentary contact switch that allows the driver to cancel operation of overdrive.
The TC switch is located on the selector lever.
When the driver initially presses the TC switch, a signal is sent to the PCM.
The PCM uses the shift solenoids to disengage/disable overdrive operation.
At the same time, the PCM illuminates the Transmission Control Indicator Lamp (TCIL) to notify the driver that overdrive is canceled.
When the TC switch is pressed again, overdrive operation is enabled, the converter clutch is released and the TCIL is turned OFF.
Whenever the ignition is cycled (vehicle shut OFF, then started again), the TC switch is turned OFF and overdrive will be enabled, even if the TC switch had been on when the ignition was shut off.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.