Powertrain, generic · Transmission

P079B Transmission Friction Element B 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. 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.

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)

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

P07A4P07A5P2701P079AP079CP2797

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