Powertrain, generic · Transmission

P079E Transmission Friction Element E 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. P079E concerns clutch 5 and is used only by the Cadillac CT6 plug-in: slip of at least 50 rpm for 0.8 s at 350 kPa line pressure and more than 50 Nm, or 6848 J of friction energy, after one trip. Its number 5 explains why the CT6 skips letter D.

Likely causes

Clutch E 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 E 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

P07AAP07ABP2704P079AP079C

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