P0838 code definition
When a P0838 trouble code is stored it is due to a detection in the four-wheel-drive switch circuit by the Powertrain Control Module (PCM). This trouble code is restricted exclusively to all-wheel or four-wheel-drive vehicles. If the PCM stores this code in a two-wheel-drive vehicle, the PCM is most likely defective. Related codes include a P0836, P0837, and P0839 code.
What the P0838 code means
When the transfer case control system detects an irregular reading issuing from the four-wheel-drive actuator switch circuit, a P0838 trouble code is stored and the Check Engine light illuminates. When the vehicle is in use, the four-wheel-drive switch actuates the four-wheel-drive system and switches between the transfer case gear ratios.
What causes the P0838 code?
The actuator or four-wheel-drive switch failing is a common cause of a P0838 trouble code. Some other causes of a P0838 trouble code storage include bad sensors, solenoids, or switches, as well as faulty wiring or connectors.
What are the symptoms of the P0838 code?
While sometimes a P0838 trouble code can be accompanied by no obvious symptoms, the code can also result in a total transfer case failure. Other symptoms include harsh or failure in shifting or the engine stalling when coming to a stop.
How does a mechanic diagnose the P0838 code?
In addition to an advanced scanner and digital volt/ohmmeter, a mechanic also needs a manufacturer's wiring schematic with connectors views to diagnose this code. The mechanic needs to perform the following diagnostic steps:
- Inspect the wiring, connectors, and components looking for any loose connections or corroded or otherwise damaged items.
- Clear any stored trouble code and test the system, including test driving the vehicle, to see if the code returns.
- If the code returns, download the stored trouble codes and freeze frame data.
- In addition, use the manufacturer's wiring schematic to check the battery voltage coming into the input side of the four-wheel-drive circuit sensor using the digital volt/ohmmeter.
- If the mechanic detects voltage, they should next use the scanner to turn the switch to the ON position and check the output side of the switch for voltage.
- If voltage is present between the battery and the switch output, but the code persists, the mechanic should test the voltage going to the four-wheel-drive actuator.
- If no voltage is present, the mechanic should disconnect all related control modules and test the resistance between the switch and the PCM, comparing their findings to the manufacturer's specifications.
- If everything checks out, then the mechanic should test the PCM for fault.
- Once everything has been inspected and replaced or repaired, the mechanic should clear the trouble code and retest the system to see if the code returns.
Common mistakes when diagnosing the P0838 code
Rebuilding or replacing the transfer case when replacing a single component would have fixed the problem is one of the most common mistakes made by mechanics when fixing a P0838 trouble code.
How serious is the P0838 code?
The transfer case failure that sometimes accompanies a P0838 trouble code means that vehicle owners should get this code diagnosed and fixed as soon as possible. Coupled with the other common symptoms of a P0838 trouble code can make it difficult to drive the vehicle, especially when attempting to change gears or go into four-wheel drive.
What repairs can fix the P0838 code?
Repairing a P0838 trouble code requires the mechanic to perform the following:
Replace the clutch position sensor if it is not working.
Replace the PCM if faulty. The mechanic also has to reprogram the PCM when replacing it.
Need help with a P0838 code?
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This article originally appeared on YourMechanic.com as P0838 OBD-II Trouble Code: Four Wheel Drive (4WD) Switch Circuit Low and was authored by Cheryl Knight.