P1851: Transmission Transfer Case Contact Plate 'B' Open Circuit
MediumPowertrainTransmission
What does P1851 mean?
P1851 is a diagnostic trouble code indicating "Transmission Transfer Case Contact Plate 'B' Open Circuit". This means there is an electrical break in the transmission wiring — a connector may be unplugged, a wire broken, or a component has failed internally. The ECU detected no signal where it expected one.
Symptoms you may notice
- Check engine light (MIL) illuminated on dashboard
- Harsh or delayed gear shifts
- Transmission slipping
- Vehicle stuck in one gear (limp mode)
- Intermittent warning lights
Estimated repair cost
Typical range in Australia (parts + labour)
$300 – $3000 AUD
Common causes
- Damaged or corroded wiring harness
- Loose or disconnected electrical connector
- Failed transmission sensor or actuator
- Blown fuse in the related circuit
- Poor ground connection
What should you do?
This code sits in a powertrain control module. The engine or transmission can drop into limp mode or cut out, which is its own hazard in traffic or on a motorway. Get it diagnosed before your next trip rather than waiting for the next service.
Get a diagnosis for YOUR car
Code P1851 can mean different things depending on your vehicle. TorqueBot gives you a diagnosis specific to your make, model, and year.