Chassis, generic

C05ED 4WD/AWD Clutch B Stuck Engaged

Check engine lightUsually off
EmissionsNot relevant
Drive cycleRequired
Limp modePossible

Clutch B is still connected although the AWD module has ordered it to open. It is the one code of the clutch B group that a manufacturer documents in detail. Audi stores C05ED00 with symptom code 29725 in the AWD control unit J492 of quattro ultra models (A4, A5, A6, A7, Q5 and their S versions, mainly 2018–2020), and the instrument cluster sporadically reports a four-wheel drive malfunction. The first issue of TSB 2051558 (2018) had the rear differential replaced if the code came back after the test plan; since revision 3 in mid-2020 Audi names wear on the rear differential's shift fork as the cause, removes actuator 2 (V623) and fits a new fork from a repair kit instead of a new differential. Production received an improved fork material.

Likely causes

Worn shift fork in the rear differential (Audi quattro ultra)
Clutch B actuator seized in the engaged position
Welded or swollen plates on friction-type clutch B

Symptoms

  • Sporadic four-wheel drive malfunction message
  • Rear driveline keeps turning when it should be decoupled, possible noise

Repair estimate

DifficultyHardWorkshop job
Parts and labour€300–3,500
Time2–8 h

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

Parts involved

awd clutch bawd clutch b actuator

Related codes

C05ECC05EEC05EBC05DE

References: static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov, autozine.org.