What does it mean?
P1850 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: A/T Brake Band Apply Solenoid Circuit Malfunction .
Symptoms
- Check engine lamp on with a transmission warning message
- Slipping or flare on the gear change that relies on the band
- Harsh, abrupt engagement of one particular gear
- A gear missing from the shift pattern altogether
- Limp mode, rising fluid temperature and reduced drivability
Likely causes
- Solenoid winding open or shorted internally after heat or age
- Control wire shorted to ground or broken where the internal harness passes the valve body
- Fluid intrusion and corrosion in the transmission case connector
- Debris or varnish jamming the solenoid valve so it cannot stroke
- External harness chafed between the case connector and the module
- Low or degraded fluid preventing the band circuit from building pressure
- Module output driver damaged by a solenoid fault
How to fix it
- Read all codes and the freeze frame, and inspect fluid level, colour and smell
- Inspect the case connector for fluid, corrosion and terminal damage, and the external harness for chafe
- Measure solenoid resistance at the case connector and compare with specification
- Test the control wire back to the module for opens and for shorts to ground or voltage
- Command the solenoid with the scan tool and listen or watch for a state change
- Drop the pan, check the magnet for clutch and band material, and inspect the internal harness and solenoid
- Replace the solenoid, service the fluid and filter, and road test to confirm the affected shift is now clean