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P0839 is a diagnostic trouble code (DTC) for "Four Wheel Drive (4WD) Switch Circuit High". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
The P0839 code belongs exclusively to all wheel and four wheel drive vehicles. It indicates that the powertrain control module (PCM) has identified an issue within the four wheel drive switch circuit.
An OBD-II generic code, P0839 is recorded when the transfer case control system reads an abnormal signal from the four wheel drive's actuator switch circuit. This is responsible for engaging or switching from the transfer case gear ratios in the two-wheel high setting, the two-wheel low setting, neutral setting, four wheel high, or four wheel low settings.
A P0839 code may be due to:
The P0839 code can trigger a range of symptoms that include no symptoms except for the check engine indicator to the total failure of the transfer case, which means the vehicle is inoperable. The other symptoms can include difficulty in shifting, failure to down or up shift, and engine stalling when the vehicle stops.
The P0839 code is diagnosed with an OBD-II scanner and visual inspections. The mechanic first evaluates the freeze frame data to see when the code appeared, resets the fault codes and takes the vehicle for a road test. The purpose is to determine if the code reappears, and if so, to then move on to the visual inspection.
This inspection will identify any problems with the connectors or wires, and will also include repairing and replacing anything that is damaged, shorted, corroded or disconnected. The vehicle is then diagnosed again, and if the code reappears, the repairs are done.
Because the P0839 code originates with the transfer case, one of the leading mistakes made during diagnosis is that the transfer case is the issue and must be rebuilt. This is a very expensive mistake, even if it is limited to component replacements rather than an entire rebuild.
A P0839 code is very serious because it means the vehicle may suddenly become inoperable, or incredibly difficult and unsafe to drive.
The repairs needed to deal with the P0839 code will include:
Failure of the PCM is rare, but it is possible. If this is the issue, you will have to disconnect all of the modules, use the proper wiring diagram and replace all circuits needed. You will also have to remember that PCM replacement means reprogramming it to your vehicle's specifications.
YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.