What it means
Same condition as element A slip, applied to friction element C (third clutch or band).
At a glance
- Usually lights the check-engine light
How it works
Friction element C is a clutch or band inside the transmission that holds when gears using that element are engaged. The TCM uses input and output speed readings to check the commanded ratio; P079C sets when those readings indicate element C is slipping.
Common causes
Most likely first.
- Worn or damaged friction element C
- Low or degraded transmission fluid
- Hydraulic pressure loss or internal leakage
- Valve body or control fault affecting element application
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
- Review freeze-frame data and live input/output speeds to identify the gear and conditions when the ratio associated with element C slipped.
- Check fluid level and condition using the vehicle's specified method, and look for leaks or signs of overheated or degraded fluid.
- Compare the slip event with commanded gear data to verify that it occurs when friction element C should be holding.
- Check transmission wiring, connectors, and speed sensor readings for problems that could distort the calculated gear ratio.
- If the speed data is reliable, test hydraulic pressure in the element C circuit and investigate valve body faults or internal leakage.
Common fixes
- Correct low fluid level or repair an external leak using the specified fluid and procedure.
- Service degraded fluid if required by the vehicle's maintenance instructions.
- Repair a confirmed valve body or hydraulic fault affecting element C application.
- Repair or replace worn friction element C components if internal inspection confirms damage.
Can I keep driving?
Avoid towing, hard acceleration, and continued driving while the transmission slips; friction element C can overheat and suffer further wear. Stop if the vehicle loses drive or cannot hold gears reliably.
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.