4Matic Electronic Traction System, Function - GF42.35-P-1000AVG

Model 205, 253 with transmission 725.041 

Courtesy of MERCEDES-BENZ USA

Function requirements, general 

• Engine running or drivetrain operational
• Electronic Stability Program (ESP®) not switched to passive mode

The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" or "Drivetrain operational" signal over the drivetrain CAN, powertrain control unit and the suspension FlexRay to the Electronic Stability Program control unit.

Electronic traction system 4MATIC, general 

The electronic traction system improves start-off and acceleration ability on different road surfaces. Within defined limits, it prevents one of the drive wheels from spinning when starting off and accelerating, as well as brief spinning of several drive wheels when cornering.

Instead of mechanical differential locks, 4MATIC used the electronic traction system. It is activated automatically when one or more wheels lose grip on the road, and brakes them individually. As a result, the drive torque increases simultaneously at the wheels which have sufficient traction. Braking pulses occur within seconds to provide the effect of three differential locks:

• Rear axle 

  If one rear wheel is spinning, it is braked and a drive torque corresponding to the braking torque is transferred to the other rear wheel. This matches the function of a rear differential lock.

• Front axle: 

  The same principle as on the rear axle also applies for the front axle. The electronic traction system replaces the front differential lock too.

• Central lock: 

If both rear wheels are spinning, they are braked simultaneously and a drive torque corresponding to the braking torque is transferred to the front axle. The electronic traction system performs the function of a differential lock.

At low vehicle speeds, up to three wheels can be braked. This has the same effect as three differential locks, guaranteeing maximum traction.

As the vehicle speed increases, the system reduces the automatic braking pulses in order to guarantee driving stability.

If the Electronic Stability Program control unit detects that one or more wheels are spinning, the brake pressure at the spinning wheel is increased automatically to brake this wheel. To do this, the Electronic Stability Program control unit actuates the regulating valves in the traction system hydraulic unit appropriately. The resulting locking differential effect transfers the drive torque to the wheels that are not spinning.

In parallel with the wheel-selective brake interventions, the Electronic Stability Program control unit sends the "Reduce drive torque" request via the suspension FlexRay, the powertrain control unit and the engine CAN to the CDI control unit or the ME-SFI control unit. The CDI control unit or the ME-SFI control unit implements this request and sends the status of the ESP® intervention via the drivetrain CAN to the fully integrated transmission control unit. This inhibits the automatic downshift to a lower gear.

If a wheel must be braked because it is spinning, this is indicated in the instrument cluster by the Electronic Stability Program warning lamp.

The Electronic Stability Program control unit sends the request to switch on the Electronic Stability Program warning lamp via the suspension FlexRay, the electronic ignition lock control unit and the user interface CAN to the instrument cluster.