What it means
The transmission control module detected slip in friction element F. The code identifies the element; its design and function depend on the transmission.
At a glance
- Usually lights the check-engine light
How it works
The transmission control module monitors speed changes to determine whether friction element F is holding when commanded. It stores P079F when element F slips beyond the expected amount; the specific gears or operating conditions that use element F depend on the transmission.
Common causes
Most likely first.
- Worn or damaged friction element F
- 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
- Read freeze-frame data and transmission live data for commanded gear, input speed, and output speed at the time element F slip was detected.
- Check fluid level and condition using the specified vehicle procedure, looking for a low level or degraded fluid that could reduce apply pressure.
- Inspect the transmission harness and connectors for damage, corrosion, or poor contact that could disrupt element F control.
- During a controlled road test, compare commanded and actual ratios when element F is expected to hold and note the conditions that trigger slip.
- If fluid and wiring checks do not explain the fault, check hydraulic pressure and valve-body operation against the manufacturer's specification.
- If pressure and control are satisfactory, inspect element F friction material and seals for wear or leakage inside the transmission.
Common fixes
- Correct the fluid level or replace degraded fluid with the maker-specified fluid.
- Repair damaged wiring or clean and secure affected connectors.
- Repair the hydraulic leak or valve-body fault affecting element F.
- Replace worn element F friction parts or leaking apply seals.
Can I keep driving?
Avoid hard acceleration, towing, and unnecessary driving because continued element F slip can overheat the fluid and damage the transmission. If the vehicle cannot shift normally or enters limp mode, stop in a safe place and arrange recovery.
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.