P0791 Intermediate Shaft Speed Sensor Circuit

P0791 points to the intermediate shaft speed sensor circuit. The transmission controller detected a fault in the speed input used for shift and ratio calculations.

Code details

Generic OBD-II · P0

System: Transmission
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace transmission mechanical parts before checking the intermediate speed sensor signal and circuit.

Symptoms of P0791

Harsh, delayed, or slipping shifts, or being stuck in one gear.
Check-engine light, sometimes with limp-home mode.
Flaring RPM or a shudder under load.

Common causes of P0791

Low or degraded transmission fluid.
A failing speed sensor, shift solenoid, or pressure-control circuit.
Wiring, connector, or internal hydraulic/mechanical faults.

Useful checks before replacing parts

Compare intermediate shaft speed with input speed, output speed, commanded gear, and actual ratio data.
Inspect sensor wiring, connector condition, internal harness, sensor mounting, reluctor condition, and fluid contamination.
Review shift, ratio, or limp-mode symptoms that appear when the speed signal is missing or implausible.

Related OBD-II codes

These nearby transmission entries can help compare wording and pin down the fault area.