Wiper motor

The windscreen wiper motor converts the electrical signal from the steering column switch or body electronics into the mechanical reciprocating movement of the wiper mechanism. A properly functioning motor is essential for visibility in rain, snow, spray, dirt and road salt. On MAN and Mercedes trucks, buses and vans, the motor is generally combined with a gearbox, crank arm, wiper linkage and an integrated park position switch. Due to the large windscreens and long wiper arms of models including the MAN TGS, TGX, TG3, Mercedes Actros, Arocs, Citaro and Neoplan coaches, this drive is subject to considerable loads.

Windscreen wiper motors differ not only by vehicle series, but also according to model year, cab or body variant, windscreen geometry, number of wiper arms, electrical connection and control system. For example, a MAN TGL or TGM may use a different motor reduction ratio, shaft length, connector pin configuration or park angle than a TGS or TGX. Several versions are also available for the Mercedes Sprinter, Vito, Atego, Axor, Actros, Citaro and Tourismo, including motors for tandem wipers, parallelogram mechanisms or systems with separate drives.

Technically, the unit consists of a DC motor with carbon brushes, armature, permanent magnets and a reduction gearbox. The gears are generally made from steel or reinforced plastic and reduce the high speed of the electric motor to usable torque for the wiper linkage. The park contacts determine the exact resting position of the arms. An incorrect park position, wrong crank arm angle or a motor with insufficient torque may cause the wipers to strike the window seal, A-pillar or each other.

A windscreen wiper motor must therefore always be identified using the vehicle chassis number. Visual comparison or selection by model name alone is never sufficient. Also check the part number, connector configuration, mounting points, shaft diameter, output shaft length and park position.

Common complaints include slow wipers, intermittent operation, a motor that only runs at high speed, wiper arms that do not return, or a complete failure of the windscreen wiper system. Slow movement does not automatically indicate a faulty electric motor. Seized wiper spindles, corroded pivot points, bent wiper linkages or excessively loaded arms can significantly increase current draw and overload the reduction gearbox. Moisture can enter through shaft seals and connections, especially on vehicles parked outdoors or regularly driven on salted roads.

First measure the supply voltage at the motor connector under load; compare the measured value with the battery voltage. A significant voltage drop in the positive or earth cable indicates contact resistance in fuses, relays, the wiring harness, earth points or the steering column switch. Then check the current draw using a current clamp. A clearly increased current at low wiper speed often indicates mechanical resistance in the linkage, while very low or zero current is more likely to indicate an open circuit, worn carbon brushes or a faulty armature.

Remove the wiper arms and assess whether the spindles move smoothly by hand. Check the crank arms for play, worn ball joints and cracks around the press fit. If possible, test the motor without the mechanism connected: a motor that runs normally then but stalls under load usually has a mechanical rather than an electrical problem in the wiper transmission. On modern vehicles, read fault codes from the body or cab electronics; communication issues or rain sensor fault messages can also affect control.

Replace the windscreen wiper motor when the park contacts are faulty, the motor armature is burnt, the gear reduction slips or the shaft bearings have excessive radial play. Always fit a new motor together with a checked and, if necessary, reconditioned wiper linkage. Fitting only a motor to seized spindles often quickly leads to overload again.

Clean the tapered fit between the wiper arm and shaft, position the arms in the specified park position and tighten the nuts to the specified torque. Then test the low and high speeds, intermittent function, washer function and automatic return to the resting position. A technically verified fit and rapid availability of cab parts help keep downtime for trucks, buses and vans to a minimum.