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. The letter matches the manufacturer's clutch number. P079B concerns clutch 2. GM's Two-Mode flags above 200 rpm for 1 s, after two trips; the 2013 Volt above 200 rpm after one trip; Malibu Hybrid and Volt from 2016 100 rpm for 2.5 s at more than 15 Nm, or 5851 J of friction energy, after one trip. Chrysler's Pacifica PHEV lists it as friction element 2 with MIL and a permanent code.
Medium severity. Can I keep driving?Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.
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
Most likely causes
- Clutch B plates worn or glazed
- Too little line pressure: low or aged fluid, filter, auxiliary oil pump or blocked pressure orifice
- Pressure or shift valve of clutch B or valve body sticking
- Module software (false setting)
- Faulty speed signals (motor resolver, output)
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: hard
- It can trigger limp mode.
- It affects emissions.
What each character of P079B means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 7: Transmission
- 9B: Specific fault in that system
Frequently asked questions
Can I keep driving with code P079B?
Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.
What causes code P079B?
The most common causes are: clutch B plates worn or glazed; too little line pressure: low or aged fluid, filter, auxiliary oil pump or blocked pressure orifice; pressure or shift valve of clutch B or valve body sticking.
Related codes
- P07A4Transmission Friction Element B Performance/Stuck Off
- P07A5Transmission Friction Element B Stuck On
- P2701Transmission Friction Element B Apply Time Range/Performance
- P079ATransmission Friction Element A Slip Detected
- P079CTransmission Friction Element C Slip Detected
- P2797Electric/Auxiliary Transmission Fluid Pump A Performance/Stuck Off
Sources
- gsi.ext.gm.com: 13OBDG06 Hybrid Diagnostics
- gsi.ext.gm.com: 13OBDG01 Hybrid TCM Diagnostics
- gsi.ext.gm.com: 16OBDG02 Hybrid Diagnostics
- gsi.ext.gm.com: 18OBDG01 Hybrid Diagnostics
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.