What P079A means
The 'friction element slip' codes monitor a clutch that is commanded locked in a power-split hybrid transmission: the module calculates its slip from electric motor, engine and output speeds (target 0 rpm) and flags slip above a threshold for a minimum time, with sufficient line pressure and clutch torque; from 2016 GM also flags a calculated friction energy threshold at once.
How the engine computer detects it
The letter matches the manufacturer's clutch number. P079A concerns clutch 1. On GM's Two-Mode SUVs and pickups (2008–13) that is the hybrid low/1-2 clutch, flagged above 200 rpm for 3 s after one trip; GM bulletins link it to a clogged line pressure orifice and the auxiliary oil pump. The Volt flags above 200 rpm in three attempts, Malibu Hybrid and Volt from 2016 190 rpm for 0.6 s or 8003 J. Chrysler's Pacifica PHEV fixes P079A by software, as a permanent code with MIL.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light or 'service hybrid system' message
- Limp mode with reduced power or restricted drive mode
- Slipping, engine speed rises without drive
- Jolt when the engine starts or stops
Common causes
- Clutch A plates worn or glazed Most likely
- Too little line pressure: low or aged fluid, filter, auxiliary oil pump or blocked pressure orifice Possible
- Pressure or shift valve of clutch A or valve body sticking Possible
- Module software (false setting) Less likely
- Faulty speed signals (motor resolver, output) Less likely
How to diagnose P079A
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: transmission clutches, transmission valve body, auxiliary transmission oil pump, hybrid control module.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 7
- Transmission
- 9A
- Specific fault
Questions drivers ask
Can I drive with code P079A?
If the car shifts normally, drive gently to a shop. If it's stuck in one gear, slips, shifts harshly or won't move out of Park, don't drive it: have it towed.
Will my car pass an emissions inspection with P079A?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.