What does it 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.