Electronic control unit

A control unit at the central electrical distribution panel processes switching signals and, depending on the version, manages electrical consumers, relay outputs and network communication. This ECU (Electronic Control Unit) is an electronic control unit, not a mechanical steering unit. Lighting failures, unresponsive cab functions or recurring communication faults do not automatically indicate a faulty module: power supply problems and damaged wiring harnesses cause similar symptoms.

This category covers electronic control units fitted in the cab of a truck, bus or van, for example behind the dashboard, at the central electrical distribution panel, under a seat or in a cab electronics compartment. The control units fitted and their mounting locations vary by model, year of manufacture and equipment. On buses, these may include modules at the driver's workstation. The overview below covers possible functions; not every function has a separate control unit. A single module may combine several functions, and the same function may be distributed across multiple modules. There is therefore no universal, complete list for all versions. Always verify which units are actually fitted and where they are mounted using the chassis number and vehicle-specific diagrams.

The abbreviations below are common system or module designations; the terminology used varies by manufacturer and version. Not every abbreviation refers to a separate control unit. Where there is no generally established abbreviation, this is indicated.

1. (BCM) Body Control Module — Central electrical control unit or body control unit. Processes switching signals and controls electrical body and cab functions, such as lighting, windscreen wipers and relays.
2. (PDM) Power Distribution Module — Electronic distribution or power module. Distributes the supply voltage to electrical consumers and switches or protects individual outputs.
3. (CCM) Cab Control Module — Cab or convenience control unit. Manages convenience functions such as interior lighting, sleeper cab controls, sun blinds and other cab equipment.
4. (CPC) Common Powertrain Controller / (FFR) Fahrzeugführungsrechner — Vehicle management or powertrain coordination control unit. Processes driving requests and operating conditions, among other inputs, and coordinates communication between the engine, transmission, braking system and other vehicle systems.
5. (CGW) Central Gateway — Gateway or network control unit. Connects different vehicle networks and handles message exchange and, depending on the version, diagnostic access.
6. (IC) Instrument Cluster — Instrument panel or display control unit. Processes vehicle data to display road speed, engine speed, fluid levels, warnings and driver information.
7. (SCM) Steering Column Module — Steering column or steering wheel control unit. Processes signals from steering column switches and steering wheel buttons, for example for indicators, windscreen wipers, cruise control and menu navigation.
8. (EZS) Elektronischer Zündstartschalter / (EIS) Electronic Ignition Switch — Ignition switch, start authorisation or immobiliser control unit. Checks key or access authorisation and transmits start enable authorisation when the required conditions are met.
9. (ATA) Anti-Theft Alarm / (EDW) Einbruch-Diebstahl-Warnanlage — Alarm system or access control unit. Monitors for unauthorised access and processes signals from the remote control, door switches and any interior sensors.
10. (DCM) Door Control Module — Door control unit. Controls door-related functions, such as electric windows, central locking and mirror adjustment or heating.
11. (SM) Seat Module — Seat control unit. Depending on the seat specification, controls electric adjustment, memory settings, seat heating, ventilation or active suspension.
12. (HVAC) Heating, Ventilation and Air Conditioning — Climate control unit. Controls heating, air conditioning, fan speed and air distribution based on set and measured temperatures.
13. (no generally established abbreviation) Parking heater or parking air conditioning control unit. Manages cab heating or cooling while the vehicle is stationary. The control unit may also be integrated into the heating or cooling appliance.
14. (LCM) Light Control Module — Lighting control unit. Controls interior or exterior lighting and, depending on the version, monitors the connected lamps. A separate module may also manage automatic lighting control or headlamp levelling.
15. (WCM) Wiper Control Module — Wiper and washer control unit. Controls wipe intervals, wiper speeds and coordination with the windscreen washers and any rain sensor.
16. (SRS) Supplemental Restraint System — Airbag and seat belt pretensioner control unit. Monitors the safety system and activates the appropriate airbags and seat belt pretensioners when a collision is detected.
17. (ABS) Anti-lock Braking System / (EBS) Electronic Braking System — ABS or EBS brake control unit. Processes braking and wheel speed signals and controls the anti-lock function and, with EBS, electronic brake control. Only cab-mounted versions fall within this scope.
18. (ESP) Electronic Stability Program / (ESC) Electronic Stability Control — Stability control unit. Compares the intended and actual vehicle movement and requests corrective braking or powertrain interventions when necessary. This function is often integrated into the brake control unit.
19. (EPB) Electronic Parking Brake — Electronic parking brake control unit. Processes operating requests and safety conditions for applying and releasing the parking brake.
20. (ECAS) Electronically Controlled Air Suspension — Air suspension or ride height control unit. Controls vehicle ride height based on height sensor signals and operating requests. A separate cab suspension control unit may control cab height or damping.
21. (TCU) Transmission Control Unit — Transmission control unit. Controls gear selection and shift points in automatic or automated transmissions and, where applicable, clutch operation. The module is located in the cab only on certain versions.
22. (ESM) Electronic Selector Module — Selector lever or driving mode control unit. Processes the selected direction of travel, driving mode and manual gearshift requests and transmits them to the powertrain control system.
23. (RET) Retarder — Retarder or auxiliary brake control unit. Processes the requested auxiliary braking effect and coordinates it with other braking and powertrain functions.
24. (MCM) Motor Control Module / (EDC) Electronic Diesel Control — Engine control unit. Controls fuel injection, engine torque and engine protection, among other functions. It is only classed as a cab-mounted control unit when the vehicle-specific mounting location confirms this.
25. (ACM) Aftertreatment Control Module — Exhaust aftertreatment control unit. Depending on the version, monitors and controls functions such as AdBlue dosing and diesel particulate filter regeneration. It is often mounted outside the cab; only cab-mounted versions are covered here.
26. (ADAS) Advanced Driver Assistance Systems — Driver assistance or camera control unit. Processes camera, radar or other sensor signals for functions such as lane departure warning, adaptive cruise control, emergency braking assistance and traffic sign recognition. Some control units are integrated into a sensor at the windscreen.
27. (PDC) Park Distance Control / (AVM) Around View Monitor — Parking assistance or surround-view camera control unit. Processes distance sensor signals or camera images to provide manoeuvring warnings and display the vehicle's surroundings.
28. (CMS) Camera Monitor System — Mirror camera control unit. Processes images from cameras that replace conventional mirrors and controls the associated cab displays.
29. (TPMS) Tyre Pressure Monitoring System — Tyre pressure monitoring control unit. Receives measurement data from the wheel sensors and provides warnings of abnormal tyre pressure or, depending on the system, tyre temperature.
30. (HU) Head Unit — Infotainment, navigation or audio control unit. Manages media, navigation, telephony and audio playback. A separate amplifier module may process the audio signals for the speakers.
31. (TCU) Telematics Control Unit — Telematics, communication or emergency call control unit. Handles data exchange for fleet management, vehicle monitoring, communication services or an automatic emergency call, depending on the equipment fitted.
32. (DTCO) Digital Tachograph — Tachograph or trip recording module. Records driving and rest times, speed or trip data according to the function of the device fitted. This is generally a standalone electronic device rather than just a separate control unit.
33. (BEM) Battery Energy Management — Energy management or battery monitoring control unit. Monitors the available electrical energy and, depending on the version, manages load shedding, auxiliary batteries and charging functions.
34. (VCU) Vehicle Control Unit / (HCU) Hybrid Control Unit — Electric or hybrid powertrain control unit. In electrified vehicles, coordinates driving requests, energy recuperation and interaction between powertrain components. Separate battery, charging or thermal management modules may also be fitted, but are not necessarily mounted in the cab.
35. (PSM) Parametrierbares Sondermodul / (KSM) Kundenspezifisches Steuermodul — Bodybuilder interface or programmable special module. Exchanges signals between the vehicle and the bodywork and manages enable signals, engine speed requests and interlocks for additional equipment.
36. (PTO) Power Take-Off — PTO or auxiliary function control unit. Controls the engagement conditions and operation of a power take-off or connected auxiliary function, such as a hydraulic system.
37. (AAG) Anhängeranschlussgerät — Trailer or semi-trailer interface control unit. Depending on the vehicle, controls and monitors electrical connections to the trailer or semi-trailer. The trailer's own brake control unit is not a cab control unit.
38. (DCU) Door Control Unit — Bus door or passenger access control unit. Processes door commands and safety signals and controls the operation of passenger doors or boarding aids. Only modules at the driver's workstation or in a cab electronics compartment fall within this category.
39. (no generally established abbreviation) Wheelchair ramp or lift control unit. Controls a powered access ramp or lift and monitors the required safety interlocks.
40. (MUX) Multiplex — Central bus or multiplex control unit. Coordinates signals between the driver's workstation and systems such as passenger lighting, stop requests, doors and ventilation.
41. (PIS) Passenger Information System / (PA) Public Address — Passenger information or public address control unit. Depending on the installation, manages destination displays, stop information and public address functions.
42. (no generally established abbreviation) Special equipment control unit. Manages additional vehicle functions, such as warning beacons, sirens, load compartment equipment or a refrigerated body. A control panel in the cab is not necessarily the control unit itself; the actual control unit may be mounted elsewhere.

Always identify control units using the vehicle's chassis number. Visual comparison or selection based solely on the model name is never sufficient. Also check the original part number, any superseding part numbers, hardware version, software version and vehicle equipment. Identical connector housings do not guarantee matching pin assignments or output functions.

Central electrical systems may use relay-controlled distribution modules, electronically protected power modules and combined body control units. Pay attention to the nominal vehicle system voltage: typically 24 volts for trucks and buses and 12 volts for vans, always to be confirmed using the vehicle data. The permissible current per output, total module load, fuse ratings and communication protocol are determining factors. Some outputs monitor for short circuits and open circuits; unsuitable replacement lighting can therefore trigger fault messages.

On cab-specific versions, connections and parameter settings may differ between, for example, MAN TGX with an XL, XLX or XXL cab and MAN TG3 TGX with a GN, GM or GX cab. Mercedes Actros with Lang StreamSpace or Lang GigaSpace also requires verification of the exact electrical configuration.