P0800 Transfer Case Control System (MIL Request)

Description and meaning of DTC p0800

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.

p0800 diagnostic trouble code symptoms

Symptoms of a P0800 trouble code may include:Cannot shift between 2WD and 4WDInability to switch between transfer case gear rangesFlashing or constantly illuminated 4WD indicator or traction control lampUnusual noises from transfer case or driveshaft

DTC p0800 - possible causes

Causes for this code may include:Defective TCCS actuator or sensorInternal (mechanical) transfer case failureShorted or open circuits in TCCSFaulty PCM or a programming error

How to fix OBD-II diagnostic trouble code p0800

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 recommended fluid, proceed with the first step of the diagnosis. Step 1Use the scanner (connected to the vehicle diagnostic connector) to retrieve all stored codes and pertinent freeze frame data. It is a good idea to write this information down before clearing the codes then test-drive the vehicle until the PCM either enters readiness mode or the code is reset. If the PCM enters readiness mode at this time, the code is intermittent and may be much more difficult to diagnose. If this is the case, the conditions which contributed to the code being stored may need to worsen before an accurate diagnosis can be made. Step 2If the code is immediately reset, the next step of your diagnosis will require that you search your vehicle information source for diagnostic flow-charts, connector pin-out charts, connector face views, and component testing procedures/specifications. Step 3Use the DVOM to test voltage and ground circuits at the TCCS controller. If voltage and ground are detected, use the DVOM to check controller output. Begin testing components and sensors related to specific symptoms. Any components which fail to comply with recommended specifications should be considered defective. Step 4If no TCCS components have failed, use the DVOM to test system circuits. The voltage drop testing method works well for this task. Disconnect all controllers from the circuit prior to testing resistance with the DVOM. TCCS related codes are frequently attributed to the selector switchIn most cases, transfer case leaks are related to defective seals

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