On some Ford models, the Powertrain Control Module (PCM) DTC P1635 indicates that the tire size or axle ratio programmed into the PCM is not correct for the PCM calibration present in the PCM. This DTC can be caused by a modified PCM calibration, or a tire size or axle ratio programmed into the PCM that does not match the vehicle's build information.
After a new Powertrain Control Module (PCM) has been installed, the Vehicle Identification (VID) block must be programmed into the PCM.
There is a Factory Service Bulletin for the 2012 Ford Fusion
2012 Ford Fusion Factory Service Bulletin OBDII Code P1635
Check the 'Possible Causes' listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.
The cost to diagnose the P1635 2012 Ford Fusion code is 1.0 hour of labor. The diagnosis time and labor rates at auto repair shops vary depending on the location, make and model of the vehicle, and even the engine type. Most auto repair shops charge between $75 and $150 per hour.
The All-Wheel Drive (AWD) system continuously monitors vehicle conditions and automatically adjusts the torque distribution between the front and rear wheels. During normal operation, most of the torque is sent to the front wheels. If a wheel slip between the front and rear wheels is detected or the vehicle is under heavy acceleration, the AWD system increases torque to the rear wheels. When the 4X4 control module detects inappropriate mini spare or road wheels/tires (greater than 7% across the front and rear axle or 14% at one wheel) installed, this Diagnostic Trouble Code (DTC) is set.
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