P1885 Transfer Case Disengagement Solenoid Short to Battery
The P1885 code indicates that the Transmission Control Module (TCM) has detected a short circuit to battery positive (B+) in the transfer case disengagement solenoid circuit. This solenoid is responsible for mechanically disengaging the transfer case in vehicles with selectable or automatic four-wheel drive. A short to battery means the circuit has constant voltage instead of the TCM-controlled switching, preventing the disengagement mechanism from operating correctly. This code is specific to BMW and applies to xDrive or similar transfer case systems. The fault is detected when the TCM monitors the solenoid circuit voltage and sees battery voltage when it should be low (off).
01. Most Common Causes
- Transfer case disengagement solenoid with internal short circuit in the coil
- Damaged wiring insulation in the solenoid circuit causing a short to a power wire
- Solenoid connector with bent pins, corrosion, or water ingress causing a short circuit
- Transmission Control Module (TCM) with internally damaged output driver
- Aftermarket electrical modifications or additions interfering with the original circuit
02. Symptoms You Will Notice
- Check Engine Light or Transmission Warning Light illuminated
- Transfer case stuck in engaged or disengaged state, affecting four-wheel drive operation
- Possible driveline binding or unusual noises during turns
- Reduced fuel economy due to driveline drag
03. Step-by-Step Diagnosis
Scan for codes and verify P1885 is present; check for related codes.
Visually inspect the transfer case solenoid connector and wiring for damage, corrosion, or shorts.
Disconnect the solenoid and measure resistance across its terminals; compare to specifications (typically 10-30 ohms).
Check for battery voltage on the solenoid control wire with the ignition on and solenoid commanded off; voltage should be near 0V.
If wiring and solenoid are good, test the TCM output by backprobing the connector; if voltage is present when it shouldn't be, suspect a faulty TCM.
1. Frequently Asked Questions
Is it safe to drive?▼
Driving with this code is not recommended as it can cause driveline damage, loss of four-wheel drive function, or unexpected engagement/disengagement. Have the vehicle diagnosed and repaired promptly.
How much does it cost to fix?▼
Repair costs vary widely: a solenoid replacement can range from $200 to $500, wiring repairs from $100 to $300, and TCM replacement from $800 to $1,500 including programming. Diagnosis typically costs $100-$200.