P0793

What it means

P0793 is the generic code for no signal from intermediate shaft speed sensor A in the automatic transmission. The transmission or powertrain control module compares this sensor's signal with the input and output shaft speeds and the engine speed. It set the code because it saw no usable pulses from the sensor while other speed signals suggested the shaft should be turning. Whether this sensor exists, and where it sits, depends on the transmission fitted.

Symptoms

• Gearbox warning light or malfunction indicator lamp on
• Transmission goes into limp mode, often stuck in one gear
• Harsh, delayed or flared gear changes
• Erratic or non-working speedometer or rev-related gauges
• Torque converter lock-up not working, with poor economy
• Gearbox may refuse to shift up or down

Possible causes

• Faulty intermediate shaft speed sensor (internal failure or contamination with metal debris)likely
• Damaged, chafed or corroded wiring between the sensor and the control modulelikely
• Poor connection at the sensor or transmission connector, including fluid ingress into the pluglikely
• Low, degraded or contaminated transmission fluid affecting the sensor or the gearbox's internal conditionpossible
• Damaged or missing reluctor ring or tone wheel on the shaft, or a mechanical fault stopping the shaft turningpossible
• Faulty transmission control module or a software faultrare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting speed, gear and fluid temperature when the fault set
2. Check the transmission fluid level and condition, following the correct procedure for that model, as some are sealed and need specific temperature conditions
3. Inspect the sensor wiring and connectors for chafing, heat damage, corrosion and fluid in the plug
4. Compare live data for input, intermediate and output shaft speeds and engine speed to see whether the intermediate signal is missing while driving
5. Check the sensor's supply, earth and signal circuits for continuity, short circuits and voltage against the manufacturer's data
6. Test the sensor resistance or output signal against the specification for that transmission, if the sensor type allows it
7. Remove the sensor if accessible and inspect it and the tone wheel for damage and metal debris
8. Check for any relevant software updates or technical bulletins for the model and transmission

How to fix

• Replace the intermediate shaft speed sensor if it fails testing or is contaminated
• Repair or replace damaged wiring and fix poor connections, including cleaning corroded terminals
• Correct the fluid level or replace degraded transmission fluid and filter as the manufacturer specifies
• Repair or replace the damaged tone wheel or internal components if the shaft or reluctor is at fault
• Replace or reprogram the transmission control module only after the wiring and sensor are confirmed good, or if an updated calibration is a known fix for the model

Can I keep driving?

Nearby codes

• P0792GenericIntermediate Shaft Speed Sensor A Circuit Range/Performance
• P0794GenericIntermediate Shaft Speed Sensor A Circuit Intermittent