P079DTransmission Friction Element D Slip Detected
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- 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. P079D concerns clutch 4 and is used only by GM's Two-Mode SUVs and pickups (2008–13) with four clutches: slip above 100 rpm for 0.3 s at commanded pressure of at least 1800 kPa and 20 Nm torque, after two trips. Volt, Malibu Hybrid and CT6 do not use it.
- What you may notice
- 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
- Likely causes
- LikelyClutch D plates worn or glazed
- PossibleToo little line pressure: low or aged fluid, filter, auxiliary oil pump or blocked pressure orifice
- PossiblePressure or shift valve of clutch D or valve body sticking
- RareModule software (false setting)
- RareFaulty speed signals (motor resolver, output)
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €150 – €4,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.