P0800 Transfer Case Control System (MIL Request)
OBD-II Trouble Code Technical Description
Transfer Case Control System (MIL Request)
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code and applies to many OBD-II vehicles (1996-newer). That may include but is not limited to vehicles from Ford, GMC, Chevrolet, Dodge, Subaru, BMW, etc. Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration.
If your vehicle has stored a code P0800, it means that the powertrain control module (PCM) has received a data input signal indicating that the transfer case control system (TCCS) has detected a malfunction which requires malfunction indicator lamp (MIL) illumination. This type of code is applicable to four-wheel or all-wheel drive vehicles only.
The TCCS and transmission control module (TCM) may be stand alone units but are most commonly integrated into a single housing with the engine control module (ECM). This is what is referred to as the PCM.
The PCM utilizes input signals from multiple engine, transmission, and transfer case sensors to calculate automatic transmission shift strategy. The transfer case bolts to the tailshaft housing of the transmission. It is responsible for transferring engine power to the rear differential and the front differential respectively. The transmission output shaft delivers power to the transfer case which can be manipulated to transfer power to either the front or rear driveshafts (or both).
The transfer case also contains a selection of gear ranges that typically include 2HI, 4HI, 4LO, and NEUTRAL. Like power distribution, the transfer case gear range may be selected at the press of a button and controlled electronically (via the TCCS/PCM). Other vehicles must be shifted manually. Vehicles with manually shifted transfer cases do not normally exhibit this type of code.
As with many other automatic transmission/transfer case malfunctions, a transfer case control code may be caused by electrical or mechanical failure. If the PCM detects that TCCS malfunction has occurred, a P0800 may be stored and a malfunction indicator lamp (MIL) will be illuminated.
A typical 4wd switch:
What is the severity of this DTC?
A stored code P0800 indicates that a potentially serious TCCS malfunction has been detected. Conditions which contributed to a code of this nature being stored should be rectified as quickly as possible.
What are some of the symptoms of the code?
Symptoms of a P0800 trouble code may include:
Cannot shift between 2WD and 4WD Inability to switch between transfer case gear ranges Flashing or constantly illuminated 4WD indicator or traction control lamp Unusual noises from transfer case or driveshaftWhat are some of the common causes of the code?
Causes for this code may include:
Defective TCCS actuator or sensor Internal (mechanical) transfer case failure Shorted or open circuits in TCCS Faulty PCM or a programming errorWhat are some P0800 troubleshooting steps?
When diagnosing TCCS codes, you should begin by making sure that the fluid is clean and that the transfer case is filled to the appropriate level. If the fluid level is low, locate the source of the leak and repair the condition. Refill the transfer case with the recommended fluid and proceed.
A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of vehicle specific diagnostic information will be required to diagnose a code P0800.
You may use your source of vehicle information to locate a technical service bulletin (TSB) that matches the vehicle year, make, and model; as well as the engine size, code/s stored, and symptoms exhibited. If you find one, it could yield helpful diagnostic information.
With the transfer case filled to the appropriate level with the recomm
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