Fault-code directory · Transmission electronics assessment
Transmission diagnosis depends on knowing what the rotating parts are doing. When an intermediate-shaft speed signal is missing or unreliable, the controller may struggle to judge the selected ratio correctly. That can produce secondary warnings as well as poor shifting.
Codes covered
P0791 · P0792 · P0793 · P0794
P0791–P0794 cover intermediate-shaft speed sensor A circuit, performance, no-signal and intermittent conditions. This is a different measurement from engine speed, wheel speed or the transmission output speed. Confirm the component named by the actual gearbox report.
Confirm the full description, suffix and reporting module for your vehicle. These are diagnostic starting points, not a parts replacement list.
Evidence that helps narrow the fault
- Log the affected shaft signal with the other relevant speed channels under a suitable test condition. A single channel dropping out while others remain plausible is useful evidence.
- Inspect the signal path and connector before condemning the sensor. Some sensors are integrated into an internal harness or electronic assembly.
- Account for the sensor technology and the rotating target. An electrical waveform can be affected by the target or installation, so circuit continuity alone is not conclusive.
Choosing the next repair step
A repair should explain whether the signal is absent at its source, lost on its route or incorrectly processed by the controller. A gearbox ratio code may be a consequence of missing information rather than a separate clutch failure. Confirm that the original speed signal is reliable after the repair.
Does a no-signal code prove that the shaft has stopped turning?
No. It means the controller did not receive the expected information. The shaft’s actual movement and the sensor circuit need separate assessment.
Talk through the fault with AXION
Send the make, model, year, full scan report and a short description of when the fault happens. Include recent repairs or programming attempts. If you do not have a scan, describe the symptoms in your own words.
Workshop assessments are arranged by appointment in Didcot, Oxfordshire. UK-wide postal module testing and remote support are available for suitable work after compatibility and scope are agreed. Please contact us before removing or posting a module.
Assessment options and appointments · Garage and trade support
Related reading
- Shift solenoid B and C codes with harsh or missing gear changes
- Shift solenoid D and E faults after transmission work
Reference for generic code terminology: Snap-on diagnostic code reference. Use the manufacturer’s current service information for the actual vehicle and test procedure. This article provides general diagnostic guidance and is not a report of a particular customer repair.