P079F
Transmission Friction Element F Slip Detected.
- Generic
- Powertrain
- Generic code
- High severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 7
- AreaTransmission
- 9F
- FaultThe specific fault in that area
What it means
P079F is a generic powertrain code meaning the transmission control unit has detected slip on internal friction element F (a clutch or brake pack). Which physical clutch or brake 'F' refers to depends on the manufacturer and transmission. The control unit sets it when input and output shaft speeds do not match the commanded gear ratio while that element is applied.
Symptoms
- Engine revs rise without matching acceleration during a gear change or under load
- Delayed, harsh or flared shifts
- Loss of drive in one or more gears
- Transmission stuck in a limp-home gear
- Gearbox warning light or malfunction indicator lamp on
- Burnt smell from the transmission fluid
Possible causes
- Worn or glazed friction plates in the clutch or brake pack for element Flikely
- Low, degraded or contaminated transmission fluidlikely
- Low hydraulic pressure from a worn pump, internal seal leaks or a blocked filterpossible
- Faulty shift or pressure control solenoid, or a sticking valve body valvepossible
- Faulty input or output speed sensor, or wiring and connector fault giving false slip readingspossible
- Outdated transmission control unit software where the manufacturer has issued a fix for known slip detection or shift problemsrare
How to diagnose
- Read all stored and pending codes with freeze frame data, noting gear, temperature, load and speed when the fault set
- Check the transmission fluid level, condition and smell using the manufacturer's procedure, as the method varies by model
- Inspect the transmission wiring, connectors and speed sensors for damage, corrosion or fluid ingress
- Review live data for input speed, output speed, gear ratio and slip in each gear to see when slip occurs
- Check live line pressure or solenoid commanded versus actual values where the transmission supports it
- Check for manufacturer service bulletins and whether a control unit software update applies to the vehicle
- Inspect the fluid and pan for metal or friction material debris to judge internal wear
- Carry out a pressure test or internal inspection if the cause is still unclear, following the model-specific procedure
How to fix
- Correct the fluid level and renew degraded fluid and filter to the manufacturer's specification
- Repair or replace faulty speed sensors, wiring or connectors
- Replace the faulty solenoid or repair the valve body
- Repair or replace the pump or seals if hydraulic pressure is low
- Overhaul or replace the transmission with new friction elements if the clutch or brake pack is worn
- Apply an updated transmission control unit calibration only where the manufacturer lists it as a fix for this fault
Can I keep driving?
High severity
Limit driving and avoid it where possible, because continued slip burns the friction material and can cause severe internal damage. Have the car inspected promptly, and do not tow or load the car heavily meanwhile.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.