Chassis, generic

C05EC 4WD/AWD Clutch B Performance/Stuck Disengaged

Check engine lightUsually off
EmissionsNot relevant
Drive cycleRequired
Limp modePossible

Clutch B was commanded to connect, but speed signals or actuator feedback show that it carries no torque or has stayed open. In disconnecting systems the second clutch is often a positive shift element rather than a friction pack: Audi's quattro ultra releases both a gearbox-side multi-plate clutch and a decoupler in the rear differential, which autozine describes as an electromechanically operated dog clutch on the right half shaft. For this unit Audi's guided fault finding can end in replacing actuator 2 (V623) or the driveshaft speed sensor G970, as its bulletins note. BorgWarner's dog-clutch patent uses a single Hall sensor to confirm sleeve speed and position before full torque is allowed. No manufacturer publishes a C05EC case; C05ED is the reverse, a clutch that will not open.

Likely causes

Clutch B actuator sticking or too weak to shift the sleeve
Worn shift fork or damaged dog teeth in the rear differential
Worn friction plates on twin-clutch units
Low or wrong fluid in the rear drive unit

Symptoms

  • AWD malfunction message, vehicle drives on the front axle only
  • Wheel spin and traction control interventions on slippery roads

Repair estimate

DifficultyHardWorkshop job
Parts and labour€200–3,000
Time1–6 h

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

Parts involved

awd clutch bawd clutch b actuator

Related codes

C05EDC05EEC05EBC05EFC05DD

References: webwire.com, autozine.org, static.nhtsa.gov, patents.google.com.