Maintenance Required Lamp/Indicator: Description and Operation

GF00.20-P-0004RC Active Service System (ASSYST PLUS), Function
- MODEL 171.4 as of model year 09/YoM 08 model refinement package

General function requirements
- Circuit 15 On

Active service system (ASSYST PLUS), general
The ASSYST PLUS calculates when the vehicle is due for a service. The calculation takes place in the central gateway control unit (N93). As well as distance-dependent and time-dependent variables, quality factors are also taken into consideration in the determination of the service scope and the service interval.
The information is displayed via the upper multifunction display (A1p13) in the instrument cluster (A1), to which it is transmitted via the interior CAN.

ASSYST PLUS is comprised of the following partial functions:
- Function sequence for determining the remaining distance
- Function sequence for determining the remaining time
- Function sequence for evaluating data
- Function sequence for service display
- Function sequence for service reset

Function sequence for determining the remaining distance
The partial function is comprised of the following subfunctions:
- Determining the mileage
- Weighting the mileage

Determining the mileage
The warning threshold for the remaining distance is primarily decisive for the service warning if the remaining distance reaches the service warning threshold before the remaining time. The ASSYST PLUS warning threshold is stored in the central gateway control unit and can be parameterized using STAR DIAGNOSIS. When the remaining distance is being determined, the wheel speed detected by the left front rpm sensor (L6/1), the right front rpm sensor (L6/2), the left rear rpm sensor (L6/3) and the right rear rpm sensor (L6/4) is read in by the ESP and BAS control unit (N47-5) and relayed via the engine compartment CAN. The instrument cluster calculates the travel distance from values received. The main odometer reading is transmitted to the central gateway control unit via the interior CAN.'
The remaining distance to the next service is determined by the counter-check with the travel distance reading stored at the last service.

Weighting the mileage
The following driving conditions are taken into account for the weighting of the mileage:
- Cold starts
- Engine speeds
- Short-distance trips

The remaining distance and thus also the maintenance interval can be extended or shortened by the weighting.
In the process it is also taken into account whether the vehicle is actually being driven or whether the engine is being operated at idle. The current operating conditions of the vehicle are transmitted from the ME-SFI [ME] control unit (N3/10) via the engine compartment CAN to the central gateway control unit, which evaluates the transmitted information accordingly. With the best assessment only 0.6 km is taken into account for each kilometer that has been driven, which extends the remaining distance and therefore also the maintenance interval.

However, with the worst assessment 3.0 km can be taken into account for each kilometer driven, which reduces the remaining distance and therefore also the maintenance interval.

The weighting of the mileage has no influence on the display of the maintenance interval or the remaining distance. The evaluation only runs in the background and can be read out via STAR DIAGNOSIS. Depending on the national coding, a fixed maintenance interval of 8000 km, 10,000 km, 15,000 km, 20,000 km, 25,000 km or 1 year is stored in the maintenance interval display software.

Function sequence for determining the remaining time
The remaining time warning threshold is primarily decisive for the service warning, if the remaining time reaches the service warning threshold before the remaining distance. The remaining time warning threshold is stored in the central gateway control unit and can be parameterized using STAR DIAGNOSIS.

Function sequence, evaluation of data
Apart from the evaluation factors which depend on the real driving conditions, quality factors for determining the service scope and intervals are taken into account by ASSYST PLUS.

The following variables are transmitted to the central gateway control unit via the engine compartment CAN for this purpose:

from the ESP and BAS control unit:
- Vehicle lateral acceleration

from the ME-SFI [ME] control unit
- Pedal value
- Engine speed
- Engine oil pressure
- Engine oil level
- Engine torque
- Engine temperature
- Engine off time

Function sequence for service display
The following notes with service code can be displayed in the upper multifunction display:
- Service X in XX days
- Service X in XXXX km or miles
- Carry out Service X

The service date is displayed at least 1000 km or 30 days before the next service is due. The service scope provides information on the scope of the service operations to be performed.

Function sequence for service reset
The service can be reset via the left multifunction steering wheel button group (S110) and the trip odometer reset button (A1s3). The requests via the multifunction steering wheel button group are read in via the Local Interconnect Network (LIN) by the steering column tube module (N80) and relayed to the instrument cluster via the interior CAN.