Remote protection

Distance monitoring systems monitor the gap to vehicles ahead and, depending on the vehicle's equipment, support adaptive cruise control, collision warnings and automatic emergency braking. Radar sensors, electronic control units and, where fitted, front cameras work together with the braking and powertrain control systems. When faults occur, diagnosis must distinguish between a defective component, obstructed detection and sensor misalignment. A fault message does not automatically mean that the radar module needs replacing.

Always identify parts using the vehicle's chassis number. Visual comparison or selection based solely on the model name is never sufficient. On MAN TGX and TGS, Mercedes Actros and Arocs, for example, as well as suitably equipped buses and vans, radar modules differ by year of manufacture, equipment code and system generation. Check the part number, any superseding part numbers, connector pin assignments and required software version.

Distinguish between ACC (Adaptive Cruise Control), which maintains the set following distance, and AEBS (Advanced Emergency Braking System), which can intervene when a collision is imminent. Both functions may use the same radar sensor, but the functions supported vary by version. Engine variants are mainly relevant indirectly through the vehicle configuration and communication with the powertrain control system; the engine family alone does not determine sensor selection.

Important design parameters include the nominal supply voltage, typically 24 volts on heavy vehicles and often 12 volts on vans, the detection range, the field of view and the specified mounting tolerances. Many front radar sensors operate at around 77 gigahertz; always check the specifications for the version concerned. Antenna characteristics, bracket geometry and the radar transparency of plastic covers are also critical. A module that fits mechanically is therefore not necessarily functionally interchangeable.

Common complaints include adaptive cruise control cutting out, warnings about limited sensor visibility and implausible object detection. Dirt, ice, damaged covers or unapproved paint coatings can weaken radar signals. After a minor collision, a bent sensor bracket can alter the sensing direction without any visible damage to the electronics. Moisture ingress and chafing in the wiring harness can also cause intermittent power supply or communication faults.

1. Read out all relevant control units using suitable diagnostic equipment. Record fault codes, freeze-frame data and the conditions under which the complaint occurs before clearing the fault memory.
2. Inspect the sensor surface, cover, mountings and connectors. Check whether accessories or bodywork components are obstructing the specified detection field.
3. Use a multimeter to measure the supply voltage at the sensor under load and the voltage drop across the supply and earth circuits. Compare the results with the vehicle-specific limits; a continuity test without load does not rule out excessive contact resistance.
4. For communication faults, check the CAN (Controller Area Network) connection against the wiring diagram. If necessary, assess the waveform using an oscilloscope. Only measure resistance with the circuit de-energised, following the manufacturer's procedure.
5. Compare live detection values and alignment data with the diagnostic instructions. On combined systems, also investigate camera faults and missing signals from the braking control system.

Repair damaged wiring, seals or sensor brackets first. Replace radar modules if internal defects or housing damage are confirmed. Observe the specified tightening torques and use only suitable fasteners: play or distortion affects the sensing direction.

After replacement, removal or a change in mounting position, coding and static or dynamic calibration may be necessary. First check tyre pressures, ride height and vehicle alignment in accordance with the manufacturer's procedure. Use the specified calibration target and measurement distances; generic angle or distance values cannot be relied upon. Finish with a controlled functional check and a fault code check. Never test automatic emergency braking with improvised obstacles on public roads.