Low, degraded or contaminated transmission fluid; Worn clutch or brake pack friction material in element C; Faulty shift or pressure control solenoid for the element C circuit; Low hydraulic pressure from a worn pump, blocked filter or internal seal leakage; Faulty input or output speed sensor giving a false slip reading; Wiring or connector fault in the gearbox harness, or valve body wear; Outdated transmission control unit software on models with a known shift adaptation issue.

P079C

Transmission Friction Element C 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
9C: FaultThe specific fault in that area

What it means

P079C means the transmission control unit has detected slip in friction element C, which is a clutch or brake pack inside an automatic or dual-clutch gearbox. It sets when the measured input and output speeds do not match the ratio expected for the commanded gear while that element is meant to be applied. Which physical clutch is 'C' depends on the gearbox design, so the exact element must be confirmed for the specific model.

Symptoms

Engine revs flare or rise without matching acceleration during a gear change or under load
Delayed, harsh or slipping engagement in one or more gears
Gearbox warning light or malfunction indicator lamp on
Gearbox defaulting to limp mode or a fixed gear
Burning smell from the transmission fluid
Poor acceleration or juddering under load

Possible causes

Low, degraded or contaminated transmission fluidlikely
Worn clutch or brake pack friction material in element Clikely
Faulty shift or pressure control solenoid for the element C circuitpossible
Low hydraulic pressure from a worn pump, blocked filter or internal seal leakagepossible
Faulty input or output speed sensor giving a false slip readingpossible
Wiring or connector fault in the gearbox harness, or valve body wearrare
Outdated transmission control unit software on models with a known shift adaptation issuerare

How to diagnose

Read all stored codes and freeze frame data to see gear, load, temperature and speeds when the slip was logged
Check for related codes such as other slip, solenoid or speed sensor faults and deal with those first
Check transmission fluid level, condition and smell using the correct procedure and temperature for the model
Inspect the gearbox wiring, connector and speed sensors for damage, corrosion, leaks or fluid ingress
Check live data for input speed, output speed and the calculated slip ratio in the affected gear
Test solenoid resistance and operation and check commanded versus actual line pressure where the model allows
Check for a manufacturer technical bulletin or software update relevant to the vehicle
Carry out a pressure test or gearbox inspection if fluid, electrical and sensor checks are all fine

How to fix

Correct the fluid level and replace degraded fluid and filter using the specification for the gearbox
Replace a faulty speed sensor, solenoid or damaged wiring and connectors
Repair or replace the valve body or pump if pressure is low
Overhaul or replace the gearbox if the element C clutch pack is worn
Update the control unit software where an outdated calibration is a known cause, then carry out any adaptation procedure

Can I keep driving?

High severity

Limit driving and avoid it where possible, as continued slip quickly burns the clutch material and can turn a minor repair into a gearbox rebuild. If the car must be moved, drive gently for a short distance only and have it checked promptly.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.