Technical Description of OBD-II Trouble Code
The circuit for the Transmission Range Sensor “B” is experiencing low voltage.
What does that mean?
This code is a generic powertrain code that applies to all makes and models from 1996 onwards. However, the specific troubleshooting steps will vary depending on the vehicle.
This code is a generic powertrain diagnostic trouble code (DTC) that relates to the transmission control system. It is classified as a type “C” DTC, which does not trigger the check engine light but may cause the overdrive (O/D) or D4 indicator to blink. Only emission-related codes will cause the check engine light to illuminate.
The transmission range sensor operates by receiving a voltage signal that changes or reroutes according to the position of the gear shifter. In the DTC description, it indicates a low condition in the circuit, meaning there is low or no voltage signal returning to the PCM. Refer to the diagram in the diagnosis/repair section below for more information.
Example of an external Transmission Range Sensor (TRS):
TRS image from Dorman
Symptoms & Severity of Code
The engine may exhibit a no-start condition due to the park/neutral switch, which is internal in most transmission range sensors. It could also experience erratic shifting or possibly start in gear. Additionally, there may be a lack of power due to the transmission controls being in “limp home” mode.
There is a significant safety factor associated with this code, and it should be repaired as soon as possible.
Causes
Potential causes for this code to be set are:
Diagnostic and Repair Procedures
To diagnose this code, we must first have a basic understanding of two things:
1. What is an Open Circuit?
An open circuit is a circuit that does not complete a loop from battery negative to battery positive. For example, if a light bulb stops working because the filament broke in half, the circuit would be open at the broken filament.
2. What is a Short Circuit?
A short circuit occurs when battery negative comes into contact with battery positive without some type of load in between the two. In other words, there must be a component (e.g., a light, a motor, a sensor, etc.) in the circuit. A short circuit is similar to dropping a wrench on top of your car battery and having it touch both terminals, causing sparks. This is known as a direct short.
Now that we have covered some basic circuit knowledge, refer to the diagram below. An open circuit at point A, B, or C would cause low voltage to the PCM. A short circuit at the same points would cause a blown fuse and, again, low voltage at the PCM. Both of these conditions will trigger DTC P2802.
To determine the exact cause of the DTC, simply check for voltage at points A, B, and C. If there is voltage at A and B but not at C, suspect a faulty range sensor. If there is voltage at C, suspect shorted wiring or, in rare cases, a faulty PCM based on my experience. If there is voltage at A only, check the fuses.
Related Transmission Range Sensor codes: P2800, P2801, P2803, and P2804.
