P0838 Four Wheel Drive (4WD) Switch Circuit Low
OBD-II Trouble Code Technical Description
Four Wheel Drive (4WD) Switch Circuit Low
What does that mean?
This is a generic powertrain diagnostic trouble code (DTC) and applies to many OBD-II vehicles (1996-newer). That may include but is not limited to vehicles from Chrysler, Ford, Jeep, General Motors, Dodge, Chevrolet, Mercedes, etc. Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration.
OBD-II trouble code P0838 and related codes P0836, P0837, and P0839 are associated with the four wheel drive (4WD) switch circuit. This circuit is also known as the transfer case control circuit.
The purpose of the 4WD switch circuit is to allow the driver to select the actuation of the 4WD system and change the transfer case gear ratios from two wheel high, two wheel low, neutral, four wheel high, and four wheel low as required based on the configuration.
When the PCM or TCM detects voltage or resistance within the 4WD switch circuit that is too low, below the normal range threshold, code P0838 will be set and the check engine light, 4WD malfunction light or both may be illuminated.
A four wheel drive selector switch:
What is the severity of this DTC?
The severity of this code is normally moderate, but 4WD switch circuit problems may be severe if the transfer case is stuck in low gear which causes unwanted stress on internal transmission and engine components requiring immediate attention. In some circumstances, the vehicle may not move or shift into gear at all.
What are some of the symptoms of the code?
Symptoms of a P0838 trouble code may include:
Transfer case stuck in one gear Vehicle will not go into gear at all Transmission shifts harshly 4WD malfunction light illuminated Check engine light illuminatedWhat are some of the common causes of the code?
Causes for this P0838 code may include:
Defective 4WD switch Transfer case malfunction Faulty or damaged wiring Loose or defective control module ground strap Corroded, damaged or loose connector Defective fuse or fuse-able link (If applicable) Defective PCM or TCMWhat are some P0838 troubleshooting steps?
The first step in the troubleshooting process for any malfunction is to research the Technical Service Bulletins (TSB's) for the specific vehicle by year, model and power plant. In some circumstances, this can save a lot of time in the long run by pointing you in the right direction.
The second step is to check the transmission and transfer case fluid to check the condition and confirm it as at the appropriate level. Then locate all components associated with the 4WD switch circuit and look for obvious physical damage. Based on the specific vehicle, this circuit may incorporate several components including the transfer case, switches, solenoids, the PCM and TCM. Perform a thorough visual inspection to check the associated wiring for obvious defects such as scraping, rubbing, bare wires, or burn spots. Next is to check the connectors and connections for security, corrosion and damaged pins. This process must include all wiring connectors and connections to all components including the PCM and TCM. Consult the specific tech data for the vehicle to verify the configuration and see if a fuse or fuse-able link is incorporated into the circuit.
Advanced Steps
The advanced steps become very vehicle specific and require the appropriate advanced equipment to perform accurately. These procedures require a digital multi meter and the specific technical references for the vehicle.
Voltage Checks
The reference voltage and the acceptable ranges may vary based on the specific vehicle and the circuit configuration. Specific technical data will include troubleshooting charts and the appropriate sequence to follow
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