System Overview

System overview

Control module




The role of the central electronic module (CEM) is 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
- lock
- immobilizer
- headlamps
- headlamp range adjustment (certain markets)
- parking lamps
- front fog lamps
- rear fog lamps
- back-up lamp
- high level stop lamp
- turn signal lamps
- wiper/washer windshield/rear window/headlights (wiper/washer for rear window only C30/V50)
- headlamp washer
- roof hatch
- rain sensor
- horn
- clock
- seat belt reminder
- interior roof lighting
- sun visor lighting
- courtesy/glove compartment lighting
- cargo compartment lighting
- fuel level
- fuel pump
- corrosion preventative fuel tank (only B4184S8)
- rear windshield heating
- electrically heated seats
- memory function for power seats
- power supply (generator control)
- starter motor
- current limiting
- LEDs in doors for lock indication (only C70)
- LEDs in switch roof movement (2008-) (only C70)
- alcolock (option 2009-)
- secondary battery (2010-, only vehicles with the function automatic start/stop of engine)
- regenerative charging (only in vehicles with the brake energy regeneration function 201020-)
- daytime running lights (from structure week 201044, option).
The control module is below the glove compartment on the passenger side. 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 control module contains two processors. One is connected to both the high and low speed sections of the controller area network (CAN). The other is only connected to the low speed section.
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 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.