Maintenance Required Lamp/Indicator: Description and Operation

GF00.20-P-0004GM Active Service System (ASSYST PLUS), Function
- MODEL 164.1 as of model year 09/YoM 08 model refinement package
- MODEL 164.8, 251.0 /1 as of model year 09/YoM 08

General function requirements
- Circuit 15 On

System in general
The Active Service System (ASSYST PLUS) determines the vehicle's respective service time point. 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.
Computation of the maintenance interval display (WIA) takes place in the central gateway control unit (N93). This forwards a corresponding request over the engine compartment CAN to the instrument cluster (A1). The display is then shown on the multifunction display (A1p13).

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 service display
- Function sequence for service reset

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

Function sequence for 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 warning threshold is filed in the internal maintenance computer of the central gateway control unit, and is notified to the instrument cluster.

When the remaining distance is being determined, the wheel speed detected by the left front rpm sensor (L6/1), right front rpm sensor (L6/2), left rear rpm sensor (L6/3) and right rear rpm sensor (L6/4) is read in by the ESP control unit (N47-5) and transmitted over the engine compartment CAN to the instrument cluster. It then calculates the travel distance using the received values.
The remaining distance to the next service is determined by the counter-check with the travel distance reading stored at the last service.

The main odometer reading is saved continuously to the nonvolatile part of the instrument cluster's internal memory. This memory guarantees the retention of the counter reading for at least five years even when the voltage supply is decoupled.

Function sequence for weighting the mileage
The following driving conditions are taken into account for the weighting of the mileage:
- Oil temperatures
- Engine speeds
- Short-distance trips

The oil level check switch (S43) (except with engine 629.9) has been installed for monitoring the engine oil level. On vehicles with engine 629.9, the oil sensor (oil level, temperature and quality) (B40) is installed for this purpose.
The engine speed is registered by the crankshaft Hall sensor (B70). The ME-SFI [ME] control unit (N3/10) (with gasoline engine) or the CDI control unit (N3/9) (with diesel engine) reads in the respective information. If necessary a message is transmitted to the instrument cluster via the engine compartment CAN.

The vehicle's current operating conditions are sent by the ME-SFI [ME] control unit or the CDI control unit over the engine compartment CAN to the maintenance computer, which then evaluates the transmitted data. The best evaluation is 0.6 km for each actual kilometer driven.
The poorest evaluation is 3.0 km for each actual kilometer driven. 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, the maintenance interval display (WIA) software has a fixed maintenance interval of 8000 km, 10,000 km, 15,000 km, 20,000 km or 25,000 km or a year.

Function sequence for determining the remaining time
The remaining time warning threshold is primarily decisive for the service warning, if the remaining time is reached before the remaining distance. The warning threshold is stored in the instrument cluster and can be read out using STAR DIAGNOSIS.

Function sequence for service display
The following text messages can appear in the multifunction display:
- Service XX in XX days
- Service XX in XXXX km or miles
- Carry out service XX
- Service XX overrun by XX days
- Service XX overrun by XXXX km or miles

The display is rounded up/down to the nearest 100 km or five days. The message can be displayed automatically as a remaining distance, following a driver request or if a warning threshold is exceeded.

Function sequence for service reset
The service can be reset in the workshop level using the left multifunction steering wheel button group (S110) and right multifunction steering wheel button group (S111). In the process the display takes place in the multifunction display.
The multifunction steering wheel button groups are read in over the steering LIN from the steering column tube module (N80). Via the engine compartment CAN the signals are transmitted to the instrument cluster and to the maintenance computer.

The workshop level is activated by pressing the trip odometer reset button (A1s3) three times within a period of t = 1.5 s.