Transfer Case Control System (MIL Request)


The PCM has detected a problem in the transfer case control system. A code has been stored and the service engine light illuminated. A variety of different transfer case failure codes will trigger this code being stored in the PCM. Some models will also place the transmission in “limp in” mode along with this code being stored. Only all-wheel drive or four-wheel drive vehicles should exhibit this code. If this code is presented in a two-wheel drive vehicle, suspect a defective PCM or programming issue.

Code Set Parameters

In order for this code to be exhibited, the transfer case control system must detect an abnormal reading from one or more of its many sensors, solenoids, and/or switches. Any malfunction which causes a specific transfer case component or system failure code to be stored is capable of causing this code to be stored, as well.


Symptoms can range from none at all to total transfer case failure (that results in a stranded motorist condition). Some of the most common symptoms may include service engine soon lamp illumination, harsh shifting, failure to shift (up or down), or engine stall when coming to a stop.

Common Causes

Common causes include four-wheel drive switch or actuator failures. By far the most common cause of this code being stored originates from a low fluid condition. Catastrophic transfer case damage is frequently the result of a fluid leak that has remained unchecked over a long period of time. Other causes include faulty sensors, solenoids, or switches, and defective wiring harnesses and connectors.

Common Misdiagnosis

Technicians report that many transfer cases are totally rebuilt (at great cost to the vehicle owner) or replaced when component replacement may repair the problem. Many repair facilities opt to totally rebuild or replace transfer cases instead of repairing them. This is a viable option, particularly in high-mileage vehicles, and also helps them to cover themselves from additional failures during the perceived warranty period.


  • A scanner (or code reader) and a digital volt/ohmmeter will be helpful when diagnosing this code. This type of code applies to all-wheel drive or four-wheel drive vehicles only
  • If this code is present in your two-wheel drive vehicle, suspect a faulty PCM or programming error. This type of code is an informational code only and does not actually isolate a particular transfer case component or system failure
  • When this code is stored it simply indicates that another (more specific) transfer case code has been stored or a transfer case problem has been detected. While the majority of vehicles equipped with OBD-II diagnostic systems utilize a PCM, with the engine and transmission (transfer case included) control systems integrated into one unit, some models use a separate engine control module (ECM) and transmission control module (TCM)
  • When the TCM detects a fault from one of its many sensors, switches, or solenoids, it inputs a code of this type to the ECM
  • Other vehicle applications control the transfer case through using the traction control module
  • Even when the engine and transmission control modules are integrated, some models use this code to activate malfunction indicator lamp illumination and initiate the transmission control limp-in mode
  • In limp-in mode, electronic pressure modulation is bypassed so that maximum pump pressure can be maintained
  • Maximum pump pressure is often required to allow the transmission to shift and pull
  • Shifting will likely be harsh when the vehicle is in limp-in mode. Begin your diagnosis of this code by diagnosing and repairing all other stored transmission codes
  • Chances are that once the other codes are repaired, this code will not return because it is an information code only. Begin with a visual inspection of all wiring and connectors
  • Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
  • Always retest the system after repairs are completed to ensure success. If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
  • This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
  • Continue by clearing the code and operating the vehicle to see if it returns
  • This will help to determine whether or not the malfunction is intermittent
  • After the codes are cleared, test drive the vehicle to see if the code returns
  • If the code fails to immediately return, you may have an intermittent condition
  • Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can even be attempted