What it means
Intermediate shaft speed sensor C (third intermediate sensor in heavy-duty or hybrid-coupled transmissions) signal voltage below the lower limit.
At a glance
- Usually lights the check-engine light
How it works
Intermediate shaft speed sensor C reports the speed of a third intermediate shaft or sensing point, where fitted in some heavy-duty or hybrid-coupled transmissions. The transmission control module sets P07C9 when sensor C's signal voltage falls below its expected lower limit, often because the signal wire is grounded or its connection is poor.
Common causes
Most likely first.
- Signal wire shorted to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
How to diagnose it
- Record freeze-frame data and check live data specifically for intermediate shaft speed sensor C to see whether its reading is absent or implausible when the fault occurs.
- Locate sensor C using vehicle service information, then inspect its connector and harness for moisture, corrosion, pushed-back pins, or insulation rubbed through against ground.
- With the fault present, gently move the harness near sensor C while watching its live reading for an intermittent change.
- Check sensor C's signal wire for a short to ground and inspect its terminals for poor contact, following the vehicle wiring diagram.
- If the wiring and connections are sound, test sensor C and its supply and ground circuits against the manufacturer's specification.
Common fixes
- Clean and secure corroded or loose sensor C connector terminals, and repair damaged seals.
- Repair chafed wiring or a signal wire shorted to ground.
- Repair a pushed-back or damaged connector pin and restore proper terminal contact.
- Replace intermediate shaft speed sensor C if it fails testing.
Can I keep driving?
If shifts are normal and the warning light is the only symptom, limit driving to a short, cautious trip for diagnosis. Avoid heavy acceleration and towing; harsh shifts, slipping, or limp mode can make the vehicle unpredictable and may worsen transmission damage.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.