System Overview

System overview

Control module




The role of the central electronic module (CEM) is to control the controller area network (CAN) and to act as a bridge between the low and high speed sections of the controller area network (CAN) and the data link connector (DLC).
It also manages the following functions:
- Alarm (certain functions)
- Locks (certain functions)
- Immobilizer
- Headlamps
- Front parking lamps
- Front fog lamps
- Headlamp range adjustment (certain markets)
- Automatic range adjustment (Bi-Xenon)
- Turn signal lamps
- Courtesy lighting / key lighting / glove compartment lighting
- Fuel pump
- Wiper / washers for the windshield and headlamps
- Starter motor
- Speed sensitive power steering
- Horn
- Clock
- Power supply (generator control)
- Current limiting
- Fuel level display, gasoline / diesel
- Additional heater.
- Blind spot information system (BLIS)
The control module is to the left of the steering column under the dashboard. The entire control module is removed from the car during replacement.
A car configuration file is stored in the central electronic module (CEM). This file contains information about:
- the VIN of the car
- the structure week
- the equipment level of the car.
When replacing the central electronic module (CEM), the VIN cannot be read off until the software has been downloaded from the Volvo central database.
The central electronic module (CEM) communicates with directly connected components and with other control modules and components via serial communication and the control area network (CAN).
The central electronic module (CEM) uses built in diagnostics to check all activations and the input and output signals. A diagnostic trouble code (DTC) is stored if the control module detects a fault. In certain cases, the incorrect signal is replaced with a substitute value. Other control modules use the network to report to the central electronic module (CEM) if they have diagnostic trouble codes (DTCs) stored. This function is used when reading off diagnostic trouble codes (DTCs) without VIDA.
Any diagnostic trouble codes (DTCs) are stored in the control module memory. This information can be read off using VIDA via the data link connector (DLC) in the vehicle.
The easiest way to check if the central electronic module (CEM) is grounded and receiving power is to activate the hazard warning signal flasher. The central electronic module (CEM) is powered if the function operates.
For further information, also see Signal specifications.

Signals
The table below summarizes the input signals to and output signals from the central electronic module (CEM). The signal types are divided into directly connected signals, serial communication and controller area network (CAN) communication. The illustration below displays the same information with the Volvo component designations.