Technical Description of OBD-II Trouble Code
The circuit for Transmission Range Sensor “A” is registering a high voltage.
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to vehicles equipped with OBD-II. While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
This is a generic powertrain diagnostic trouble code (DTC) within the transmission sub-group. It is classified as a type “B” DTC, which means that the powertrain control module (PCM) or transmission control module (TCM) will not activate the check engine light until the conditions to trigger the code are detected in two consecutive key sequences (key on-off, off-on).
The PCM or TCM utilizes the transmission range sensor, also known as the inhibitor switch, to determine the position of the shift lever. If it receives signals indicating two different gear positions simultaneously for more than 30 seconds, the code P0708 will be set. If this occurs twice in a row, the check engine light will illuminate and the transmission will be placed in “fail-safe” or “limp-home” mode.
Example of an external Transmission Range Sensor (TRS):
TRS image from Dorman
Symptoms & Severity of Code
The check engine light will illuminate along with a noticeable lack of power when accelerating from a complete stop due to the transmission starting in third gear.
Continuing to drive the vehicle under these conditions could result in severe damage to the transmission. It is recommended to have it repaired immediately to avoid costly internal transmission repairs.
Causes
Possible causes for this code to be triggered include:
Diagnostic and Repair Procedures
The transmission range sensor receives a twelve volt signal from the ignition switch and sends a signal back to the PCM/TCM that corresponds to the selected position of the gear shifter.
In my experience, the most common causes of this code are a faulty range sensor or misadjusted shift cable/linkage.
Checking this circuit is easiest with a scan tool, but if one is not available, there are still a few things you can check. Keep the key in the on position with the engine off (KOEO). Using a digital volt ohm meter, you can individually check each return signal circuit by back probing at the sensor while it is still connected. Have an assistant shift to each gear one at a time. Each signal circuit should have voltage in only one position. If there is voltage present on any one circuit in more than one gear position, suspect a faulty range sensor.
In my experience, I have NEVER seen a PCM/TCM be the cause of any range sensor related DTC. This does not mean it is not possible, because it is, but it is highly unlikely. However, I have seen a faulty PCM/TCM that was damaged by a short circuit in a range sensor. If you suspect a fault in the PCM/TCM, make sure to investigate the cause of the damage before installing a new one to prevent causing the same damage again.
Related Transmission Range Sensor codes: P0705, P0706, P0708, P0708, and P0709.
