P1855
Transmission Transfer Case Contact Plate 'C' Open Circuit.
- Other
- Powertrain
- Manufacturer code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 1
- Defined byThe manufacturer
- 8
- AreaTransmission
- 55
- FaultThe specific fault in that area
What it means
P1855 is a manufacturer-specific code. Here it means the transfer case contact plate 'C' circuit is open. The control unit monitors the contact plate, which reports the selected transfer case range or position, and saw no signal or an open circuit on the 'C' line, so it cannot confirm the range. Exact wiring, terminal layout and which circuit is 'C' depend on the make, model and transfer case type.
Symptoms
- Four-wheel-drive or transfer case warning light on the dashboard
- Transfer case will not shift between ranges, or the shift indicator flashes or is blank
- Transmission or drivetrain defaulting to a fixed mode or limp-home
- Harsh, delayed or incorrect gear shifts
- Loss of four-wheel drive or low range
- Possible engine management light
Possible causes
- Damaged, corroded or loose connector at the transfer case contact platelikely
- Open circuit or chafed wiring between the contact plate and the control unitlikely
- Worn or faulty contact plate or range sensor inside the transfer casepossible
- Oil or water ingress into the contact plate connector or harnesspossible
- Poor earth or supply to the contact plate circuitpossible
- Faulty transmission or transfer case control unitrare
How to diagnose
- Read all stored and pending codes and note the freeze frame data, then check for other transfer case or transmission codes
- Check the transfer case range selector and warning indicators to see if the displayed range matches the actual position
- Visually inspect the contact plate connector and harness for damage, corrosion, oil contamination and rubbing on underbody components
- Disconnect the connector and check the terminals for pushed-back pins, green corrosion and a poor grip
- Using the manufacturer wiring diagram, test the 'C' circuit for continuity, short to earth and short to supply, and check the reference voltage and earth
- Wiggle-test the harness with live data on display to see if the signal drops out
- Check the contact plate's resistance or switch states against specification as the range is changed, if the model allows
- Check the transfer case fluid level and condition, and look for a service bulletin for your model
How to fix
- Clean, repair or replace the damaged connector or terminals
- Repair or replace the open or chafed section of wiring
- Replace the faulty contact plate or range sensor, following the manufacturer's procedure
- Dry out and seal the connector, and fix the source of oil or water ingress
- Restore the faulty supply or earth connection
- Replace or reprogram the control unit only after confirming the wiring and sensor are good and it is a known fault for the model
Can I keep driving?
The car can usually be driven carefully, but avoid using four-wheel drive or shifting the transfer case range until it is checked. Have it repaired soon, as the unit may stay in a fixed mode and shifting problems could get worse.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.