E-MAS Module Steering Axle Control Actros

Typical faults:
No diagnostic communication / CAN bus fault of the steering module
Axle does not steer or remains locked in the center, possibly with an auxiliary steering malfunction message on the instrument cluster
Intermittent steering or slow return due to solenoid valve failures, power supply faults or actuator position sensor issues
Plausibility alarms between steering wheel input and axle position feedback
Power supply failures (fuses, connectors, corrosion) causing module shutdown and activation of safe mode (centering/lock)

The A0004460220 is an electronic control unit dedicated to managing the auxiliary steering on Mercedes commercial vehicles equipped with a third steerable axle. It is commonly referred to in the aftermarket as the EHZ/E-MAS module (Elektronik – Elektronische Hinterachs-Zusatzlenkung / Electronically Controlled Multi Axle Steering) and is integrated into the electro-hydraulic system that controls the angle of the auxiliary rear axle based on vehicle speed, steering wheel angle and vehicle status. It operates on a 24 V network and communicates with the vehicle networks to exchange status and diagnostics.

Technical specifications

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

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Functions

• Dynamic control of the rear steerable axle to reduce turning radius and improve low-speed maneuverability.
• Automatic transition to centering and axle lock as speed increases to ensure stability.
• Sensor monitoring (angle, actuator position, circuit pressure) and safety mode management with recovery to center in case of failure.
• Diagnostics and fault reporting on the CAN bus with error logging and instrument cluster warnings.

Model applications

• Mercedes-Benz Actros MP2/MP3 (if equipped with EHZ rear steerable axle).

Typical faults

• No diagnostic communication / CAN bus failure of the steering module.
• The axle does not steer or remains locked in the center, possibly with an auxiliary steering fault message on the instrument cluster.
• Intermittent steering or slow return due to solenoid valve failures, power supply issues or actuator position sensor faults.
• Plausibility alarms between steering wheel input and axle position feedback.
• Power supply failures.

Final conclusions

The A0004460220 is the key control unit of the E-MAS/EHZ system for managing the third steerable axle on Actros/Atego/Axor/Econic. It ensures low-speed maneuverability and high-speed stability, with safety strategies focused on centering in case of a fault.

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