|Code||Fault Location||Probable Cause|
|P0837|| Four wheel drive switch range/performance problem |
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|Wiring, poor connection, four wheel drive switch, ECM/PCM/TCM|
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What Does Code P0837 Mean?
OBD II fault code P0837 is a generic code that is defined as “Four wheel drive switch range/performance problem”, or sometimes as “Four Wheel Drive (4WD) Switch Performance / Rationality”. This code is set when the PCM (Powertrain Control Module) detects an abnormal voltage in the four-wheel drive selector switch or its control system. Note that this code only applies to applications that are equipped with electronically controlled/selectable AWD (All Wheel Drive) or four-wheel drive systems.
NOTE: While this code specifically refers to a problem in the four-wheel drive selector switch or circuits, and NOT to mechanical problems in the drive train, it is sometimes possible for this code to cause severe damage to drive train components.
On most applications, the 4WD or AWD drive system is controlled by a multiplex switch that activates electronically (or sometimes vacuum) controlled actuators that switch the transfer case between different modes and gear sets. Thus, in a fully functional system, the driver can manipulate the switch to select between two-wheel high, two-wheel low, neutral, four-wheel high and four-wheel low settings, or modes to suit local driving conditions. In practice, the PCM “knows” which mode the drive train is in by monitoring the resistance values of each of the switches’ output circuits.
In terms of operation, the PCM supplies a 5-volt reference voltage to the switch that has known resistance values for each position. Thus, if the switch is turned to say, the low range gear ratio, the reference voltage is reduced by a predetermined resistance that is built into the switch. The resulting signal voltage is then compared to a pre-programmed value by the PCM, and if the actual and desired signal voltage values do not agree, the PCM will recognize a range/performance problem in the switch or its associated circuit(s), and it will set code P0837 as a result.
Where is the P0837 sensor located?
On most applications, the four-wheel drive selector switch is located either in the dashboard, or in the center console.
The image below shows a typical wiring diagram for a selectable 4WD system, but note that this diagram is intended for illustrative purposes only. Always refer to the manual for the application for wiring details that apply to that application.
What are the common causes of code P0837 ?
Some common causes of code P0837 could include the following-
- Defective four-wheel drive selector switch
- Damaged, burnt, shorted, or corroded wiring and/or connectors
- Mechanical failure of drive train components. Note that while this is rare, it is not altogether impossible
- Failed or failing PCM. Note that this is a rare event, and the fault must be sought elsewhere before any control module is replaced
How expensive is it to fix code P0837 ?
While prices of replacement four-wheel drive switches vary widely between applications, and even between models in the same model range, an aftermarket switch will usually cost well under $200 for most applications.
However, while OEM parts will almost always cost about double the price of aftermarket units, the use of OEM parts is strongly recommended since aftermarket parts seldom provide the same level of reliability and durability.
What are the symptoms of code P0837 ?
Some common symptoms of code P0837 could include the following-
- Stored trouble code and possibly an illuminated warning light
- One or more drive train modes may fail to engage, or disengage
- On applications with automatic transmissions, shifting may be harsh, erratic, or the transmission may not shift at all
- On automatic applications, the engine may stall when coming to a stop
- In rare cases, mechanical failure of the transfer case may occur
What are common solutions to code P0837 ?
Common solutions to code P0837 could include the following-
- Replacement of the four-wheel drive selector switch
- Replacement or repair of damaged wiring and/or connectors
How serious is code P0837 ?
Since this code can cause serious mechanical damage to drive train components, vehicles on which code P0837 is present should ideally not be driven until the code had been resolved, since the vehicle can be immobilized unexpectedly.
How safe is it to still drive the car with code P0837 ?
Since the vehicle can be immobilized unexpectedly, this code presents an obvious safety risk both in urban driving and (especially) in an off-road environment, where loss of the four-wheel drive system could result in loss of control of the vehicle.
How difficult is it to repair code P0837 ?
Resolving code P0837 should not present the average non-professional mechanic with undue difficulty if only the switch is to be replaced, or wiring is to be repaired or replaced.
However, where mechanical failure of, or damage to the drive train had occurred, the better option is to refer the vehicle to the dealer or other competent repair facility for professional diagnosis and repair.
What are the common mistakes when repairing code P0837 ?
A common mistake made when dealing with this code involves the unnecessary replacement, repair, or rebuilding of expensive drive train components that could include actuators or even complete transfer cases.
In the vast majority of instances of code P0837, the real problem is almost always nothing more serious than failures of the four-wheel drive selector switch or malfunctions in its control circuit(s) that are relatively easy and cost effective to repair.
How do you troubleshoot code P0837 ?
Record all fault codes present, as well as all available freeze frame data. This information can be of use should an intermittent fault be diagnosed later on.
NOTE: If any additional codes are present, consult the manual on the relationship(s) between these codes and P0837 before starting a diagnostic procedure. If P0837 was stored first, all subsequent codes have likely set as a reaction to P0837, and will likely clear automatically when P0837 is resolved. However, codes relating to the drive train or transmission that were stored before P0837 have likely contributed to the setting of P0837, and these codes must therefore be resolved first.
Assuming that there are no additional codes present, remove the four-wheel drive selector switch from the dashboard/console, but do not disconnect any wiring at this point.
Refer to the manual to determine the color-coding and function of each wire in each connector on the switch. Inspect the switch for visible signs of damage such as electrical arcing, overheating, discoloration, or other evidence that the switch might have suffered a malfunction. Replace the switch if such evidence is found.
If no visible evidence of a switch malfunction is found, identify the reference voltage wire, and check to see that the correct voltage (usually 5 volts) is present. Note that all electrical checks are usually done with a KOEO (Key-On-Engine-Off) condition, but be sure to consult the manual on the correct procedure to follow during this step.
If no reference voltage is present, consult the manual to determine the CORRECT pin on the PCM connector, and check that the PCM is delivering the correct voltage on this pin by back probing the connector. Resist the temptation to condemn the PCM out of hand if no reference voltage is present on this pin. Several other sensors/circuits may depend on this reference voltage as well, so if there is no reference voltage at the PCM connector, there will almost certainly be a host of reference voltage related codes present. If this is the case, replace the PCM in strict accordance with the instructions provided in the manual to ensure proper operation of the replacement PCM.
If however, there is no reference voltage at the PCM connector and there are no additional codes present, consult the manual on the correct procedure on how to test the voltage on the PCM pins directly, but take great care during this step to prevent causing accidental short circuits that can destroy the PCM. If this check reveals no reference voltage, replace the PCM in strict accordance with the instructions provided in the manual to ensure proper operation of the replacement PCM.
If however, the correct reference voltage is present at the PCM, find and repair the open circuit in the reference voltage circuit between the PCM and the four-wheel drive selector switch. Clear the code after repairs are complete, and rescan the system the see if the code returns.
If the reference voltage circuit checks out, identify the signal wire, and test the signal voltage value for each position of the switch. Bear in mind that each position has a different resistance, so compare all obtained reading with the values stated in the manual, and replace the switch if any value does not agree with the stated value.
Clear all codes and repeat Step 5 after the switch replacement to see if the code returns. If no codes return after repeatedly cycling the switch between all possible positions, the repair was successful.
NOTE: Be sure to disconnect the switch from the PCM during this step to prevent causing damage to the controller.
If the code persists, but the switch checks out, perform a thorough visual inspection of all associated wiring. Look for damaged, burnt, disconnected, or corroded wiring and/connectors, and make repairs or replace wiring as required. Clear the code after repairs are complete, and rescan the system the see if the code returns.
If no visible damage to wiring/connectors is found, perform resistance, continuity, and ground integrity checks on all associated wiring. Compare all obtained readings with the values stated in the manual, and make repairs or replace wiring as required to ensure that all electrical values fall within the ranges specified by the manufacturer. Clear the code after repairs are complete, and rescan the system the see if the code returns.
NOTE: Be sure to disconnect the switch from the PCM during this step to prevent causing damage to the controller.
In the unlikely event that the code does return, locate and identify all relevant position sensors on the drive train, and test each sensor in strict accordance with the instructions provided in the manual. These tests typically involve testing the internal resistance of each sensor; replace any sensor whose resistance does not agree with the value stated in the manual for that sensor.
Steps 1 through 7 will resolve code P0837 in nine out of every ten instances, and it is rare for this code to persist beyond the steps already outlined here. However, if the code persists, suspect one or more defective actuators, or a mechanical failure of the transfer case. In these cases, diagnosing the cause of the code might require partial or sometimes complete disassembly of major drive train components, which is generally beyond the skills of most non-professional mechanics. Thus, if a mechanical failure is suspected, refer the vehicle to the dealer or other competent repair facility for professional diagnosis and repair.
Codes Related to P0837
- P0836 – “Four Wheel Drive (4WD) Switch Circuit”
- P0838 – “Four Wheel Drive (4WD) Switch Circuit Low”
- P0839 – “Four Wheel Drive (4WD) Switch Circuit High”
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