What does it mean?
P1740 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: A/T 4th Pressure Switch Circuit Malfunction .
Symptoms
- MIL (check engine lamp) on with a transmission warning lamp
- No fourth gear or overdrive, so engine RPM stays high on the motorway
- Noticeably increased fuel consumption during longer trips
- Harsh or hunting shift into and out of top gear
- Limp mode with the transmission held in a lower gear
Likely causes
- Pressure switch failed open or shorted internally
- Signal wire open, shorted to ground or intermittently broken at a flex point
- Fluid contaminated case connector with green or white corrosion on the pins
- Low line pressure that never reaches the switch threshold in overdrive
- Stuck valve or a solenoid that fails to route pressure to the fourth gear circuit
- Worn overdrive clutch pack or leaking seals in the apply circuit
- Faulty module input, examined last in the diagnostic order
How to fix it
- Road test while logging pressure switch states, gear command and engine RPM
- Check fluid level and quality, and confirm the correct fluid type was used
- Inspect the case connector and wiring for ATF ingress, corrosion and chafing
- Test the switch for continuity change under applied air pressure on the bench
- Measure line pressure in top gear with a gauge and compare to the specification
- Inspect the valve body and filter for debris that could block the fourth gear circuit
- Replace the switch or repair the hydraulic fault, then verify overdrive engages and stays applied