Powertrain, generic · Transmission

P079D Transmission Friction Element D Slip Detected

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

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.

Likely causes

Clutch D 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 D or valve body sticking
Module software (false setting)
Faulty speed signals (motor resolver, output)

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

Repair estimate

DifficultyHardWorkshop job
Parts and labour€150–4,500
Time1–12 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

transmission clutchestransmission valve bodyauxiliary transmission oil pumphybrid control module

Related codes

P07A8P07A9P2703P079CP079A

References: gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com.