Vehicle power supply control unit, component description - GF54.21-P-4126SX
MODEL 216.3, 221.0 /1 up to Model Year 8 Illustrated on model 221
Location
The vehicle power supply control unit is under the right panel in the luggage compartment, attached to the partition wall between the passenger compartment and the luggage compartment above the onboard electrical system battery (G1).
Task
The vehicle power supply control unit is responsible for evaluating the on-board electrical system battery and starter battery (G1/4) and for controlling the 2-battery on-board electrical system. The basic functionalities are:
- Improving starting reliability by coupling the on-board electrical system battery and the starter battery in critical conditions and with cold starts
- Charging the starter battery via the charge converter
- Minimizing the quiescent current by opening and closing the quiescent current cutout relay (N82/1k1)
- Providing voltage in the on-board electrical system by controlling the supply of power, e.g. consumer shutoff for the "engine ON" and "engine OFF" operating conditions
- Providing protection via the front prefuse box (F32)
- Ensuring the availability of as many comfort functions as possible
- Controlling the on-board electrical system emergency mode in critical supply situations
The vehicle power supply control unit is connected to the chassis CAN to allow data to be exchanged.
Body
The vehicle power supply control unit contains the following components:
- On-board electrical network line pyrofuse temperature sensor (N82/1b1)
- On-board electrical network line pyrofuse (N82/1f1)
- Fuse 2 (N82/1f2)
- Fuse 3 (N82/1f3)
- Fuse 4 (N82/1f4)
- Fuse 5 (N82/1f5)
- Fuse 6 (N82/1f6)
- Fuse 7 (N82/1f7)
- Fuse 8 (N82/1f8)
- Fuse 9 (N82/1f9)
- Fuse 10 (N82/1f10)
- Quiescent current cutout relay (N82/1k1)
- Microcontroller
- Charge converter
Function
The voltage is picked off on the supply battery main path in the vehicle power supply control unit. The microcontroller monitors the state of charge of the on-board electrical system battery by reading in the voltage value and determining the average voltage in the onboard electrical system. It is combined with an internal temperature sensor and controls all switch functions as well as the charging of both batteries. In the case of circuit coupling, it determines the state of charge of the coupled system. These measurements provide data for all functions of the vehicle power supply control unit.
When the vehicle is in operation, the charge converter is used for recharging the starter battery. It regulates the charging voltage according to temperature. With "circuit 15 OFF", the charge converter is also switched off if it was in operation for at least 1 h beforehand.
To enable a longer service life, the consumers (circuit 30g) are disconnected from the power supply by the quiescent current cutout relay after a programmed time has expired.
Consumers (circuit 30g) are:
- Left instrument panel fuse box (F1/7)
- Front SAM control unit with fuse and relay module (N10/1)
- Rear SAM control unit with fuse and relay module (N10/2)
The on-board electrical network line pyrofuse in the vehicle power supply control unit protects the on-board electrical network line to the front prefuse box. It is triggered by the following parameters:
- Temperature of on-board electrical network line higher than approx. 140 °C (up to 31.7.05)
- Crash signal from restraint systems control unit (N2/7)
The vehicle power supply control unit checks whether the pyrofuse has been triggered. A triggered pyrofuse is stored in the fault memory of the vehicle power supply control unit. The pyrofuse is only monitored if the vehicle power supply control unit is not in the bus idle state.