Scheme 85
Brief description of components
Single-axle electronic height control largely comprises the following components
- Air supply unit The air supply unit includes the following components: Electric motor for driving compressor Compressor with air drier Drain valve with pressure-holding and pressure-limitation function Electric control valve Solenoid valve block with 2 solenoid valves (2/2-way valves)
- EHC control unit The EHC control unit (EHC = electronic height control) decides on a case-by-case basis whether there is a need for intervention to compensate for changes in load. Besides height control, the EHC control unit also has the task of monitoring system components and of storing and displaying faults.
- 2 air springs The air springs are located in place of the steel springs. The air springs form the airtight, moving connection between the body and the wheel carrier. The air pressure in the air spring supports the vehicle's weight. The air springs and the impact absorbers are separate components.
- 2 level sensors The EHC control unit receives information about the ride height on the left and right-hand sides of the vehicle from the level sensors. The level sensors are installed on the rear axle.
- Check Control A fault in the single-axle electronic height control is indicated on the LCD display with a Check-Control symbol (yellow). The text for the Check-Control message can be called up in the Central Information Display (CID).
The following control units are involved in the operation of the single-axle electronic height control (in alphabetical order)
- CAS: Car Access System The CAS (Car Access System) controls the relay for terminal 30g on the rear electrical distributor. This allows the EHC control unit to be activated and deactivated in a defined manner. The CAS supplies the terminal status (e.g. terminal 15 ON or OFF) to the EHC control unit via the K-CAN.
- DME or DDE: Digital engine electronics or digital diesel electronics The digital engine electronics/digital diesel electronics supplies the EHC control unit with the "engine running" signal. Signal path: DME or DDE -> PT-CAN -> SGM or KGM or JBE -> EHC control unit
- DSC: Dynamic Stability Control DSC (Dynamic Stability Control) supplies the following signals to the EHC control unit: Vehicle road speed Lateral acceleration
- FRM: Footwell module E70, E71 The footwell module evaluates the status of the Hall sensors in the door contacts. The footwell module transmits a message on the K-CAN to the CAS control unit (CAS: Car Access System).
- HUD: Head-up display A fault in the single-axle electronic height control system is shown in abbreviated form in the head-up display. The Check-Control symbol in the instrument cluster lights up. The related Check-Control message is displayed in abbreviated form.
- JBE: Junction box electronics E70, E71 The junction box electronics are the gateway between the PT-CAN (powertrain CAN) and the K-CAN (body CAN). The D-CAN (diagnosis-on CAN) is connected to the junction box electronics.
- KBM: Body basic module E61 The basic body module emits a signal concerning the status of the tailgate (open or closed) and the rear doors. Signal path: Boot-lid contact switch, rear door contact -> direct wire -> KBM -> K-CAN -> EHC control unit
- KGM: Body gateway module from 09/2005 E61 From 09/2005, the vehicle electrical system has been modified. The body gateway module supersedes the safety and gateway module (SGM). The body gateway module is the gateway between the PT-CAN (powertrain CAN) and the KCAN (body CAN). Until 03/2007, the diagnosis wire is connected to the body gateway module. From 03/2007, the D-CAN (diagnosis-on CAN) supersedes the previous diagnosis interface in all countries.
- KOMBI: Instrument cluster The EHC control unit (EHC = electronic height control) sends a message through the bus communications system to the instrument cluster. The instrument cluster supplies a Check Control via the Check-Control symbol in the LCD display.
- SGM: Safety and gateway module up to 09/2005 E61 The SGM (safety and gateway module) is the gateway between: PT-CAN (powertrain CAN) K-CAN (body CAN) Byteflight The diagnosis wire is connected to the SGM.
- TMFA and FMBF: Driver's door module and front-passenger door module up to 09/2005 E61 The door modules (driver's door module = TMFA, front-passenger door module = TMBF) supply a signal about the status of the front doors (OPEN or CLOSED). Signal path: Door contact -> TMFA/TMBF -> byteflight -> SGM -> K-CAN -> EHC control unit From 09/2005, the body gateway module (KGM) delivers a signal confirming the status of the front doors (OPEN or CLOSED). Signal path: KGM -> K-CAN -> EHC control unit