Function: Transfers Quattro AWD torque to rear wheels via crown wheel/pinion (4.25:1 ratio) with integrated electronic differential lock.

Key Features:

• Hypoid Gearset: Case-hardened steel (HRC 60+) with lapped contact pattern

• Haldex Coupling: Gen 5 multi-plate clutch (0-100% rear bias)

• Thermal Management: Temperature sensor triggers cooling protocol (>250°F)

Failure Modes:

• Bearing Pitting: Contaminated fluid (G 055 529 A2) causes whine

• Clutch Pack Wear: Leads to AWD disengagement (P189C codes)

• Seal Leaks: Differential fluid migrates to Haldex unit

Critical Specs:

1. Backlash: 0.08-0.12mm (requires dial indicator)

2. Pinion preload: 1.2-1.8 Nm rotational torque

Pro Tip: Perform adaptation reset via ODIS after service – prevents false "AWD malfunction" warnings.