Compatible OEM Part Numbers

Technical Specifications

Product Description

This is a refurbished original Siemens Haldex 4th generation control unit with part number 0AY907554A. The unit has been fully restored, resealed with new silicone, and bench-tested to ensure functionality equivalent to a new module. It manages the rear AWD coupling system, controlling the engagement and pressure of the rear differential clutch pack based on driving conditions.

What This Control Unit Does

• Monitors rotational speed differences between front and rear axles
• Controls the hydraulic pump pressure for rear differential clutch engagement
• Activates rear-wheel drive distribution automatically when traction is required
• Communicates with ABS, ESP and engine management modules
• Manages the N373 Haldex control valve for clutch pressure regulation
• Protects the coupling system from thermal overload

Vehicle Compatibility

The 0AY907554A is compatible with the following VAG group vehicles equipped with Haldex 4th generation AWD systems. Always verify the part number on your existing unit:

Volkswagen

Audi

Škoda

SEAT

Common Diagnostic Fault Codes

A defective Haldex 4th gen control unit commonly triggers one or more of the following fault codes:

Installation & Calibration

Installation Steps

• Locate the Haldex control unit mounted on the rear differential / rear axle assembly
• Disconnect the electrical connector and remove all mounting fasteners
• Carefully remove the old control unit from the coupling housing
• Position the replacement unit and secure all mounting points
• Reconnect all electrical connectors and verify secure fitment
• Connect a VAG-compatible diagnostic tool and code the unit to the vehicle
• Clear all stored fault codes and perform a test drive
• Confirm AWD engagement using the diagnostic tool after the test drive

Recommended Maintenance at Time of Installation

• Replace Haldex control valve N373 at the same time as fitting the new control unit
• Replace Haldex oil when replacing the control unit
• Inspect the wiring connector and harness for corrosion or damage
• Check AWD system fuses dedicated to the Haldex circuit
• Clear all stored diagnostic fault codes after installation and perform a test drive

Why Haldex Control Units Fail

1. Water Ingress & Corrosion

The control unit is located near the rear axle in an exposed position. Over time, moisture can penetrate the housing, corroding the internal circuit board and causing communication failures or complete loss of AWD function.

2. Power Supply Faults

The Gen 4 Haldex system relies on dedicated 12V supply lines protected by fuses. Blown fuses, corroded pins, or damaged wiring at the rear connector are a common cause of total AWD loss, often without an obvious dashboard warning.

3. Thermal Stress

Extended high-load driving or repeated AWD engagement can generate excessive heat that degrades solder joints and internal electronic components within the control unit over time.

4. Neglected Haldex Oil

Old or contaminated Haldex fluid leaves deposits that clog internal hydraulic passages and accelerate wear on the pump and N373 valve, leading to incorrect control unit readings and eventual AWD failure.

Quality Assurance & Warranty

12-Month Warranty: This refurbished Haldex control unit has been fully tested and is covered by a 12-month warranty against functional defects under normal operating conditions.

Warranty Coverage Includes:

• Electronic control unit malfunctions
• Communication failures with AWD, ABS or ESP modules
• N373 valve control circuit defects
• Internal calibration memory errors

Warranty Exclusions: Damage resulting from incorrect installation, incompatible vehicle fitment, external electrical faults, or physical damage during handling.

Questions or Need Help?

Our technical team is ready to assist with compatibility checks, installation guidance, and coding support.

Important Purchase Information