What does it mean?
P1731 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Problem in Shift Control System .
Symptoms
- Transmission stays in one gear or refuses to upshift under load
- Very harsh, delayed or slipping shifts with RPM flare between gears
- MIL (check engine lamp) on with a transmission warning lamp
- Limp mode that limits road speed and pulling power
- Hot fluid smell and rising transmission temperature during longer drives
Likely causes
- Shift solenoid stuck open or closed by varnish, debris or a failed winding
- Shift valve sticking in a worn valve body bore so the circuit never strokes
- Low fluid level or low line pressure from a worn pump or leaking seal
- Burnt or contaminated ATF with a clogged filter restricting the apply circuits
- Worn clutch packs or a damaged band that cannot hold the commanded gear
- Open, shorted or intermittent wiring in the solenoid harness or case connector
- Corrupted adaptive values or a module fault after repeated failed shifts
How to fix it
- Check fluid level, colour and smell, then confirm the correct fluid specification was used
- Record commanded gear against actual gear ratio on live data through a full road test
- Command each shift solenoid with the scan tool and confirm the ratio responds
- Measure solenoid resistance at the case connector and inspect the internal harness for leaks
- Connect a pressure gauge and compare line pressure with the specification in each range
- Drop the pan, inspect the filter and magnet for clutch material and metal
- Clean or replace the valve body and solenoids, and overhaul the unit if the clutches are worn