Mirror Driver Vertical Feedback Potentiometer Circuit Short to Ground

OBD II fault code B2327 is a manufacturer specific code that is defined by Ford, Lincoln, Mazda, Mercury, and Nissan as “Mirror Driver Vertical Feedback Potentiometer Circuit Short to Ground” and on these applications, code B2327 is set when the PCM (Powertrain Control Module) or, Body Control Module, detects a short circuit in an electronically controlled side view mirrors’ feedback loop.

NOTE: In this definition, “Vertical feedback” refers to the circuit that controls the movement of the mirror around the vertical (side-to-side) axis, and “Potentiometer” refers to the device in the mirror that provides the controller with information on the mirrors’ position relative to a base setting.

In practical terms, the adjustment and control of side view mirrors is accomplished by small electric motors that can tilt a mirror either from side to side (vertical axis), or up and down, (horizontal axis), or both at the same time, depending on the application. On many, if not most, applications, the amount of movement is programmable, meaning that one or both mirrors can be programmed to move only within a range set by the programmer.

To enable programming, each drive motor is connected to a potentiometer, which is a type of variable resistor that passes a variable voltage, depending where in its rotation the moving part of the potentiometer (aka, the wiper) stops on a resistive winding or strip. Refer to the image below. If the wiper is stopped halfway along the resistive strip, the potentiometer will theoretically pass only 50% of the voltage that entered it.

Therefore, by moving the wiper to different positions on the resistive strip, the exiting voltage can be adjusted to serve as a sort of baseline reference voltage a controller can use to move a mirror between an upper and lower voltage limit. Thus, when a mirror is being programmed, the controller will remember both the upper and lower limits of the voltage generated by the potentiometer during the programming procedure.

However, during the mirror’s movement, the current that is allowed to pass through the potentiometer also serves as a form of feedback, and the controller will cut power to the actuator when either the previously programmed upper or lower voltage limit is reached. In practice, when this feedback voltage is interrupted or absent, the controller cannot control the mirror and code B2327 will be set, which depending on the application, may, or may not trigger a warning light.

The image below shows detail of the mechanics of an electronically adjustable/controlled side view mirror. Note the two drive motors and the potentiometer that is geared to each. Note that each motor controls adjustment of the mirror around one axis. Be aware that while the example shown here is somewhat typical, the actual arrangement and appearance of the various components in an adjustable mirror can differ greatly between applications.