P079A
Transmission Friction Element A Slip Detected
Friction element A (the first clutch or band in the gear matrix) shows measurable slip while it should be fully engaged. Detected by comparing input/output speed sensors against the commanded gear ratio. Slip means the element cannot transmit full torque — risk of glazing the friction surfaces.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: hard
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
Common causes
Ordered by how often each turns out to be the cause.
- Worn friction discs in element ACommon
- Low hydraulic pressure to element APossible
- Old ATF lacking friction modifierPossible
Parts involved
- Clutch Pack A
- Transmission Fluid
P079A is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.