What does it mean?
P1728 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Transmission Range Sensor D Circuit High .
Symptoms
- MIL (check engine lamp) on and the gear position display shows a dash or the wrong range
- Engine cranks in gear, or does not crank at all in Park and Neutral
- Reverse lamps stay off or come on in the wrong range
- Harsh default shift schedule, or the transmission holds one gear
- Delayed engagement when moving the selector between Drive and Reverse
Likely causes
- Worn or internally corroded transmission range sensor with dirty contacts
- Shift cable or linkage out of adjustment so the sensor never reaches the detent
- Short to battery voltage on the D circuit from a chafed harness
- Open circuit or lost ground on the sensor return path, which also reads as high
- Water, salt or road spray corrosion inside the range sensor connector
- Loose sensor mounting bolts allowing the sensor body to rotate out of position
- Module input circuit failure, checked only after wiring and adjustment are verified
How to fix it
- Compare the selector position with the range shown on the scan tool in every detent
- Inspect and adjust the shift cable so the sensor lines up in Neutral before anything else
- Backprobe the D circuit and record its voltage in each range against the specification
- Test the circuit for a short to battery voltage with the sensor unplugged
- Check continuity and resistance of the sensor ground and reference wires
- Clean or repair the connector, replacing corroded terminals rather than the whole harness
- Replace the range sensor, then verify the start inhibit and reverse lamp functions