System Overview

Central Electronic Module (CEM)

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
- the 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
- speed sensitive power steering
- 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-)

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.

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.

Input signals Output signals

Directly connected: Directly connected:
- Horn switch - Parking lamps
- Trunk lid, unlocking - License plate lighting
- Deadlocking switch - Brake light
- Stop lamp switch - Dipped beam
- Fuel tank filler cap, - Passenger compartment
unlocking lighting
- Private locking switch - Fog tail lamps
- Control signal for - Hazard warning signal
doors/hatches (x6) flasher indicator lamp
- Blower fan, re-supply - Shift lock
- Twilight sensor - High level stop lamp
- Sun sensor - PAD-warning light (passenger
airbag disconnected warning lamp)
- Fuel level sensor - PAE-warning light (warning
light activated airbag
passenger) (2008-)
- The DC/AC converter - Seat belt reminder
fuel tank (only B4184S8)
- Fuel level sensor (AWD) - Fuel tank filler cap, unlocking
- Seat belt buckle sensor, - Turn signal lamps
rear (x3)
- Supplemental Restraint - Malfunction indicator
System Module (SRS), lamp (MIL).
collision output signal
- Hazard warning signal - Alarm LED
flasher switch
- Vicinity signal, - Mass movement sensor module
ignition key (MMS), power supply
- Dip switch - Steering Column Lock Module
(SCL), wake-up (does not
apply to USA/CDN market
for 2009-).
- Sun roof speed signal - Engine control module
(ECM), stimulation
- Washer fluid level sensor - Dimmer switch, instrument
lighting
- Fuel pump, re-supply - Trunk lid, unlocking
- Brake fluid level switch - Receiver, power supply
- Reverse gear sensor - Sun roof, closing signal
- Parking brake switch - Frequency signal, electrical
additional heater
- Clutch pedal sensor - Frequency signal blower fan
(5 cylinder petrol engines
with manual transmissions)
- Clutch pedal switch - Indicator lamp, deadlock
(diesel engines with
manual transmissions)
- Accelerator pedal - Passenger seat sensor,
(AP) position sensor supply voltage
- Battery temperature - Fuel pump, relay
sensor (replaced by software
starting from structure
week 200605)
- Outside temperature gauge - Infotainment relay
- Light switch module (LSM) - Rear windshield washer, relay
- High beam, relay
- Front windshield washer, relay
- Rear demist, relay
- Extended power supply, relay
- Passenger compartment lighting
(power supply)
- Reversing lamp, relay
- Ignition switch interlock, relay
- Front fog lamps, relay
- Headlamp washer, relay
- Horn, relay
- Tailgate wiper, relay
- Light switch module (LSM)
- LEDs in doors for lock
indication (only C70)
- LEDs in switch roof movement
(only C70, 2008-)
- Humidity sensor, voltage
supply (option, only ECC 2008-)
- Alcolock, voltage supply
(option 2009-)

Via serial communication: -Via serial communication:
- Gas discharge lamp module - Gas discharge lamp module
(GDL) (2 pcs.)(optional equipment) (GDL) (2 pcs.) (optional
(-2007, only S40/V50) equipment) (-2007, only S40/V50)
- Remote control receiver - Remote control receiver
- Rain sensor module - Rain sensor module
(RSM) (optional extra) (RSM) (optional extra)
- Steering Column Lock - Steering Column Lock
Module (SCL) (does not apply Module (SCL) (does not
to USA/CDN market for 2009-). apply to USA/CDN market
for 2009-).
- Siren control module - Siren control module
(SCM) (optional extra) (SCM) (optional extra)
- Start control module (SCU) - Start control module (SCU)
- Wiper motor module (WMM) - Wiper motor module (WMM)
- Sun roof module (SRM) - Sun roof module (SRM)
- Humidity sensor - Humidity sensor (option,
(option, only ECC 2008-) only ECC 2008-)

Via Controller Area Network Via Controller Area Network
(CAN) communication: (CAN) communication:
- Accessory electronic - Accessory electronic module
module (AEM) (optional extra) (AEM) (optional extra)
- Brake control module (BCM) - Brake control module (BCM)
- Climate control - Climate control module (CCM)
module (CCM)
- Combustion preheater - Combustion preheater module
module (CPM) (optional extra) (CPM) (optional extra)
- Driver door module (DDM) - Driver door module (DDM)
- Driver information - Driver information module (DIM)
module (DIM)
- Engine control module (ECM) - Engine control module (ECM)
- Electrical power steering - Electrical power steering
module (EPS) module (EPS)
- Infotainment control - Infotainment control module (ICM)
module (ICM)
- Passenger door module (PDM) - Passenger door module (PDM)
- Phone module (PHM) - Phone module (PHM) (optional extra)
(optional extra)
- Power seat module (PSM) - Power seat module (PSM)
(optional extra) (optional extra)
- Supplemental restraint - Supplemental restraint
system module (SRS) system module (SRS)
- Steering wheel module (SWM) - Steering wheel module (SWM)
- Transmission control module - Transmission control module
(TCM) (optional extra) (TCM) (optional extra)
- Trailer module (TRM) - Trailer module (TRM)
(optional extra). (optional extra).
- Convertible Roof Module - Convertible Roof Module
(CRM) (only C70) (CRM) (only C70)
- Headlamp Control Module - Power seat module, left
(HCM) (2008-, only S40/V50) (PSL) (only C30/C70)
- Power seat module, right
(PSR) (only C30/C70)
- Headlamp Control Module
(HCM) (2008-, only S40/V50)