Code Definition

P0791 — Counter gear speed sensor circuit signal error - Sensor 1

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About P0791

P0791 is a generic (obd-ii standard) powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P0791 is stored, the module has detected a sensor-related fault — the reported value from the named sensor is out of spec.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P0791 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The fault code P0791 is set when the transmission control module (TCM) or the engine control module (ECM) in vehicles with integrated control systems detects an error in the signal from the intermediate shaft (or counter gear) speed sensor, also referred to as Sensor 1. This sensor plays a crucial role in providing data about the speed of the intermediate shaft within the transmission, which is vital for the TCM/ECM to manage gear shifts effectively. A signal error indicates that the sensor is not providing accurate or consistent speed information, potentially leading to issues with shifting a...

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