This is the most effective way to diagnose without removing parts.
Code P1827 triggers when the TCM/ECM receives a signal from the range switch that does not correspond to any valid gear position. Essentially, the computer is asking, "Where is the shifter?" and the switch is replying with gibberish or a voltage reading that falls into a "gray area" between defined gears. P1827 Suzuki Swift
OBD-II scanner, Digital Multimeter (DMM), Suzuki service manual (for pin-outs), 10mm socket, and ramp/jack stands. This is the most effective way to diagnose