P079B High Generic / SAE

P079B: Transmission Friction Element B Slip Detected

What to do

Ask how many slip faults are stored. Several at once almost never means several worn clutches — it means the fluid, the pressure or the pump, which every one of them shares. That single question can be the difference between a service and a rebuild.

Say whether it slips when the car is cold, when it is hot, or both. Slipping only when hot points at fluid and pressure; slipping from cold points at wear inside. It is genuinely useful and only you can report it.

Say when the fluid was last changed and whether the correct specification went in.

Drive gently until it is repaired. Slip makes heat, heat destroys the fluid, and the degraded fluid causes more slip — this fault accelerates itself.

What this code means

The second friction element is slipping under load rather than holding.

The mechanism is element A's, and what a second lettered element adds is a pattern worth reading before any decision is made.

Each element is used in several gears, not one, which is what makes the comparison informative:

One element slipping points at that element, its apply circuit, or its solenoid. The gears it is used in will misbehave and the others will not — so the pattern of which gears feel wrong identifies it as surely as the code does.
Several elements slipping together almost never means several worn clutch packs. It means the fluid, the pressure, or the pump — something every element shares. That distinction is the difference between a service and a rebuild.

So the single most useful question here is how many slip codes are stored. It costs nothing to ask and it changes the quote entirely.

The other thing worth establishing is when it slips. An element that holds when cold and slips when hot points at fluid and pressure, because both fall away with temperature. One that slips from cold points at the friction material itself.

Fluid remains the cheapest and most common cause, and its specification matters as much as its level — transmission fluid is the friction modifier, not just the hydraulic medium.

Likely causes

Start here

Low or degraded transmission fluid · moderate
Worn transmission friction element · specialist
Faulty pressure control solenoid · specialist

Less common

Worn clutch packs · specialist
Debris in the transmission fluid · specialist

Symptoms

Components involved

Information, not instruction

CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.

Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.

Community experience

Be the first to write this up

Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.

What makes one worth reading:

The car — make, model, year and engine. The same fault behaves differently on each.
What you measured, not only what you replaced.
What actually fixed it — or that nothing did, which is worth knowing too.