P1842: Transmission Transfer Case Differential Lock-Up Feedback Switch Circuit Failure

P1842 is a powertrain code relating to the transfer case differential lock-up feedback switch circuit. This switch provides the transmission control module with confirmation that the differential lock-up has actually engaged when commanded. A circuit failure here means the module is not receiving a usable signal, either because the signal is absent, erratic, or outside its expected range. Without reliable feedback, the system cannot confirm whether the transfer case is in the intended state.

Common causes include a failed feedback switch within the transfer case, damaged or corroded wiring in the circuit between the switch and the transmission module, or a faulty connector. Because this is a circuit failure rather than a specific open or short designation, the fault could be intermittent. Checking the connector and wiring harness at the transfer case is a sensible starting point, followed by testing the switch itself for correct operation across its range of positions.

P1842 is rated medium severity. The transfer case may still operate mechanically, but the control system is flying blind when it comes to confirming lock-up status. This can affect how the vehicle manages traction in demanding conditions. Have the circuit and switch inspected, particularly if you rely on 4WD or differential lock for off-road or poor-weather driving.