Powertrain, generic · Transmission

P079A Transmission Friction Element A Slip Detected

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
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. 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.

Likely causes

Clutch A 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 A 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

P07A2P07A3P2700P079BP2797P0C2B

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