E-Mas module for steering axle management - Mercedes Actros MP4/MP5

The A0004463320 is an electronic control unit dedicated to managing the auxiliary axle steering on Mercedes commercial vehicles equipped with a third steering axle. It is commonly referred to in the aftermarket as the E-MAS (Electronic Multi-Axle Steering) / EHZ (Elektrohydraulische Zusatzlenkung) module and is integrated into the electrohydraulic system that commands the angle of the auxiliary rear axle according to speed, steering wheel angle and vehicle status. It operates on a 24 V network and communicates with vehicle networks to exchange status and diagnostics.

Technical specifications

• Supply voltage: 24 V.
• Interfaces: sensor inputs (steering/actuator position, speed, status), outputs for solenoid valves and the pump of the auxiliary electrohydraulic steering circuit.
• Communications: vehicle CAN for exchange of states, authorizations and diagnostics with chassis modules (FR/CPC, instrument cluster).
• Control function: reads the steering wheel/speed and calculates the angle of the steering axle; manages "active", "return-to-center" and "lock in straight line" modes at high speed.
• Hardware: sealed automotive unit with microcontroller, power stage for actuators and fail-safe management (lock/centering in case of fault).

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Functionality

• Dynamic control of the rear steering axle to reduce turning radius and improve low-speed maneuverability.
• Automatic transition to centering/locking of the axle as speed increases to ensure stability.
• Monitoring of sensors (angle, actuator position, circuit pressure) and management of safety strategies with recovery to center in case of fault.
• Diagnostics and fault reporting on the CAN network with error logging and dashboard warnings.

Applicable models

• Mercedes-Benz Actros MP4/MP5

Typical faults

• The control unit does not communicate with the diagnostic tool.
• The axle does not steer or remains locked at center.
• Intermittent steering or slow return.

Final conclusions

The A0004463320 is the key control unit of the E-MAS/EHZ system for the management of the third steering axle on Actros MP4/MP5. It ensures low-speed maneuverability and high-speed stability, with safety strategies focused on centering in case of anomalies.

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