Low, degraded or contaminated transmission fluid; Worn clutch or brake friction material in element D; Low or erratic hydraulic pressure from a faulty solenoid or valve body wear; Blocked transmission filter or restricted fluid passages; Worn pump or internal seal leakage reducing apply pressure; Wiring or connector fault to the pressure control solenoid or speed sensors giving false slip readings; Outdated transmission control software where a known update addresses slip detection or shift strategy.

P079D

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

What it means

P079D is a generic powertrain code meaning the transmission control unit has detected slip on friction element D, which is one of the clutches or brakes inside the automatic transmission. It sets when the measured input and output speeds, or turbine speed against the expected gear ratio, show the element is not holding as commanded. Which clutch or brake 'D' refers to depends on the transmission design, so check the manufacturer's information for the specific model.

Symptoms

Engine revs flare between gear changes
Delayed or harsh engagement when selecting drive or reverse
Slipping under load or acceleration in particular gears
Transmission warning light or malfunction message on the dash
Car goes into limp mode and stays in one gear
Burnt smell from the transmission fluid

Possible causes

Low, degraded or contaminated transmission fluidlikely
Worn clutch or brake friction material in element Dlikely
Low or erratic hydraulic pressure from a faulty solenoid or valve body wearlikely
Blocked transmission filter or restricted fluid passagespossible
Worn pump or internal seal leakage reducing apply pressurepossible
Wiring or connector fault to the pressure control solenoid or speed sensors giving false slip readingspossible
Outdated transmission control software where a known update addresses slip detection or shift strategyrare

How to diagnose

Read all stored codes and freeze frame data, noting gear, load, temperature and speeds when the fault set
Check transmission fluid level, condition and smell using the manufacturer's procedure, as some units are sealed and need a temperature-controlled check
Inspect the transmission wiring, connectors and speed sensor plugs for damage, corrosion or fluid ingress
Look for external fluid leaks around the pan, seals and cooler lines
Use live data to compare input speed, output speed and commanded gear to spot slip, and watch solenoid duty or line pressure if available
Check for other related codes such as solenoid, speed sensor or pressure faults that point to the root cause
Perform a line pressure test as per the manufacturer's specification, where the model allows
Check whether a software update is listed for the transmission control unit for this model

How to fix

Correct the fluid level or change the fluid and filter using the specified type
Repair or replace damaged wiring, connectors or faulty speed sensors
Replace the faulty pressure control solenoid or repair the valve body
Clean or replace blocked filters and clear restricted passages
Overhaul or replace the transmission if the clutch or brake pack, pump or seals are worn
Apply a manufacturer calibration update to the control unit only if an outdated calibration is a confirmed cause

Can I keep driving?

High severity

Avoid driving more than necessary, as continued slip quickly burns the friction material and can destroy the transmission. If it must be moved, keep speeds and loads low and get it to a workshop soon.

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