What does it mean?
P1738 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: A/T 2nd Pressure Switch Circuit Malfunction .
Symptoms
- MIL (check engine lamp) on with a transmission warning lamp
- Harsh, delayed or missing second gear engagement
- RPM flare between first and third as second gear is skipped
- Limp mode locking the transmission into a single gear
- Rising fluid temperature and reduced acceleration under load
Likely causes
- Pressure switch stuck open or stuck closed internally
- Open circuit, short to ground or high resistance in the switch signal wire
- ATF contaminated case connector with corroded or pushed-out pins
- Low line pressure so the circuit never reaches switching pressure
- Sticking shift valve or a failed solenoid that never fills the second gear circuit
- Worn clutch or seal in the second gear apply circuit leaking pressure away
- Module input circuit failure, only after the switch and wiring are verified
How to fix it
- Monitor all pressure switch states on live data through each gear and compare with the commanded gear
- Check fluid level and condition before touching the electrical side
- Inspect the case connector and internal harness for fluid ingress and corrosion
- Measure switch continuity with the circuit unpressurised, then again with pressure applied
- Connect a pressure gauge and confirm line pressure meets specification in second gear
- Drop the pan and inspect the filter, magnet and solenoid screens for debris
- Replace the pressure switch or valve body assembly, then confirm switch states follow gear changes