Part 1

Function

Alarm
See Design and Function, Alarm.

Central locking
See Design and Function, Central locking.

Immobilizer
See Design and Function, Immobilizer.

Generator (GEN) (Alternator control module (ACM))




See Design and Function, Generator (GEN).

Current limiting




The central electronic module (CEM) (4/56) communicates with the alternator control module (ACM) (6/26) via LIN-communication. In this way the central electronic module (CEM) receives information about how much current the generator produces and how much current can be used for the various loads in the vehicle.
The central electronic module (CEM) uses the prevailing outside temperature to calculate the voltage at which the battery should be charged.
Under certain conditions the generator cannot produce enough current for those loads which are connected. The central electronic module (CEM) communicates with the climate control module (CCM) (3/112) which then completely or partially switches off the following loads:
- electrical additional heater
- rear demist
- electrically heated seats
- heated door mirrors.
The central electronic module (CEM) also transmits a request via the Control area network (CAN) to the engine control module (ECM) to increase the engine idle speed.
When the engine is not running all current is taken from the battery. There are a number of different loads which can be activated when the engine is not running, for example the infotainment system (XC90). The central electronic module (CEM) continuously monitors the voltage level of the battery. When the voltage level is too low the central electronic module (CEM) transmits information to the infotainment control module (ICM) (16/1) which then shuts off the infotainment system. In the event of a fault, the central electronic module (CEM) transmits data via the Control area network (CAN) to the driver information module (DIM) (5/1) which displays a text message to the user.
If the infotainment system used in key position II, when the engine is not running, the information is sent to the driver information module (DIM). A message is displayed if the infotainment system is switched off for 2 minutes.

Charge voltage




To charge the battery optimally the central electronic module (CEM) calculates the output voltage from the generator (GEN) using the temperature of the battery. The alternator control module (ACM) controls the output voltage, depending on the control from the central electronic module (CEM). See the illustration above. In some driving conditions for example, the engine control module (ECM) is able to affect generator (GEN) control, whereby the output voltage will deviate from the above.

Controlling functions and menu selection using the steering wheel buttons
See:
- Design and Function, audio module (AUM) Applies to the S60, V70, XC70 and S80
- Design and Function, Road traffic information system (RTI). Applies to the S60, V70, XC70 and S80
- Design and Function, multimedia module (MMM). Applies to XC90
- Design and Function, engine management system
- Design and Function, phone module (PHM).

Trip computer and displaying/erasing text messages




The left-hand control stalk is used to control the trip computer and to display and erase text messages in the driver information module (DIM) (5/1).
The steering wheel module (SWM) (3/254) transmits data to the central electronic module (CEM) using LIN communication to indicate the selected function. The central electronic module (CEM) (4/56) forwards this data to the driver information module (DIM) via the CAN network.
The trip computer menu is controlled using the ring on the left-hand control stalk. Turn the ring forwards or backwards to scroll through the menu one step at a time. Some menu selections, such as average speed and fuel consumption, can be reset using the RESET button.
Error messages displayed in the driver information module (DIM) display are erased using the READ button.
For additional information about the trip computer and text messages, see Design and Function, driver information module (DIM).

Headlamps




Depending on the position of the knob, the light switch module (LSM) (3/111) transmits information via serial communication to the central electronic module (CEM) to turn on low beam. The central electronic module (CEM) (4/56) then transmits a control signal to activate the low beam relay. The bulbs are then supplied with power.
To change to high beam, the left-hand control stalk is pulled towards the steering wheel. The serial communication signal from the steering wheel module (SWM) (3/254) is transmitted to the central electronic module (CEM) which activates the high beam relay and supplies power to the high beam. For Bi-Xenon lamps, the position of the reflector is also changed so that the Xenon lamp is on at high beam.
The central electronic module (CEM) also transmits a CAN signal to the driver information module (DIM) (5/1) to light the indicator lamp for high beam.
There is a Limp Home function which ensures that low beam still works if there is a fault in the control area network (CAN). For Bi-Xenon lamps the beam is then set to the shortest range.
For further information about Bi-Xenon lamps, see Design and Function, Gas discharge lamps (GDL).

Headlamp range adjustment (certain markets)




Headlamp range adjustment is controlled by the central electronic module (CEM) (4/56). The central electronic module (CEM) communicates with the light switch module (LSM) (3/111) using serial communication.
If the thumb wheel in the light switch module (LSM) is turned, information about the position of the wheel is transmitted to the central electronic module (CEM). The central electronic module (CEM) transmits a pulse width modulation (PWM) signal to the actuator motors (6/38-39) with the pulse ratio set according to the position of the thumb wheel. The headlamp range can be adjusted in 16 stages.

Automatic range adjustment (Bi-Xenon)




Automatic headlamp range adjustment is controlled by the central electronic module (CEM) (4/56). The position sensor (7/120) on the rear suspension transmits signals to the rear electronic module (REM) (4/58) about the angle of the car in terms of the load conditions.
The rear electronic module (REM) transmits this data via the control area network (CAN) to the central electronic module (CEM) which compares the information with the table for the relevant model. The table is stored in the central electronic module (CEM).
The actuator motors (6/38-39) are then operated from the central electronic module (CEM) via a PWM signal, the pulse ratio of which depends on the angle the lamps need to be set to.

Front fog lamps




The front fog lamps (10/5-6) are activated by pressing the button for the front fog lamps in the light switch module (LSM) (3/111). The light switch module (LSM) transmits data to the central electronic module (CEM) (4/56) to light the lamps. The central electronic module (CEM) activates the relay and the bulbs are supplied with power via the relay.

Front parking lamps




Parking lamps (10/11-12) light when:
- the knob in the light switch module (LSM) (3/111) is in the low beam position
- the knob in the light switch module (LSM) is in the parking lamp position
- low beam is lit via the low beam automatic function.
The lamp switch module (LSM) transmits data using serial communication to the central electronic module (CEM) (4/56) to activate the lamps.
The lamps are supplied with power via a relay which is activated by the central electronic module (CEM). The front parking lamps have a direct power supply.
The rear parking lamps and license plate lighting are powered by the rear electronic module (REM). For further information, see Design and Function, rear electronic module (REM).
There is a Limp Home function for the parking lamps so that they will work even if there is a fault in the control area network (CAN) or in the serial communication between the light switch module (LSM) and the central electronic module (CEM).

Turn signal lamps / Hazard warning signal flashers




This function is controlled by the left control stalk. The steering wheel module (SWM) (3/254) sends data to the central electronic module (CEM) (4/56) to activate the turn signal lamps via serial communication. The central electronic module (CEM) transmits information to the driver information module (DIM) (5/1) to activate the turn signal indicator and powers the turn signal lamp.
The power supply is pulsed and the turn signal lamps are activated 90 times per minute.
The hazard warning signal flasher is activated by closing the switch (3/6) and transmits a signal to the central electronic module (CEM) to start the function. The central electronic module (CEM) transmits a signal in the same way as above, but to both sides. The central electronic module (CEM) also transmits a signal to the bulb in the switch to indicate that the hazard warning signal flashers are on. If the ignition key is in position I or II, there is a clicking sound from the driver information module (DIM). If the ignition is switched off, there is no sound, but the hazard warning signal flashers continue to flash.
If a fault occurs with a lamp, the central electronic module (CEM) detects the reduction in power consumption and the frequency is doubled on the side where the fault occurred.

High level stop lamp




For further information about the high level stop (brake) lamps, see Design and Function, rear electronic module (REM).

Courtesy lighting / key lighting / glove compartment lighting




The courtesy lighting (10/125-126), ignition switch (16/65) and glove compartment lighting (10/29) are controlled via the central electronic module (CEM) (4/56). All other interior lighting is controlled by the upper electronic module (UEM) (4/70). (See Design and Function, upper electronic module (UEM)). The central electronic module (CEM) powers the lamps which it controls directly.
The lamps are powered if a door is opened (3/74-77), or when the upper electronic module (UEM) transmits a request via the control area network (CAN). The upper electronic module (UEM) transmits a request when it has received an unlock command from one of the remote controls. If a door is opened, the central electronic module (CEM) sends a control area network (CAN) signal to the upper electronic module (UEM) to light the lighting it controls.
The glove compartment lighting (10/29) is supplied with power directly from the central electronic module (CEM) when the switch by the lamp is activated when the glove compartment is opened.

Horn




The horn is operated when the steering wheel module (SWM) (3/254) receives a signal from the switches (3/37) in the steering wheel. The steering wheel module (SWM) sends data to the central electronic module (CEM) (4/56) via serial communication indicating that the switch is closed. The central electronic module (CEM) activates the relay for power supply to the horn.
There is also a signal directly connected from the steering wheel module (SWM) to the central electronic module (CEM). This is a Limp-Home function.

Fuel pump




The central electronic module (CEM) (4/56) receives a request from the engine control module (ECM) (4/46) via the control area network (CAN) to start the fuel pump (FP) (6/33). The central electronic module (CEM) then activates the relay which supplies the fuel pump with power.
In the event of a collision in which the airbags are deployed, a signal is transmitted from the supplemental restraint system (SRS) module (4/9) to the central electronic module (CEM) which deactivates the relay for the fuel pump.

Fuel level (Gasoline/Diesel)




The fuel level is gauged by the fuel level sensors (7/130, 7/143). The signals from the sensors are transmitted to the central electronic module (CEM) (4/56). The central electronic module (CEM) calculates the remaining quantity of fuel by comparing the signals with a tank table stored internally. Information about the quantity of fuel is transmitted via the Control area network (CAN) to the driver information module (DIM) (5/1), where the fuel level is displayed on the fuel gauge.

Wipers / washers




The right-hand control stalk is moved downwards through three positions to operate the windshield wipers. The steering wheel module (SWM) (3/254) transmits information to the central electronic module (CEM) (4/56) about the selected position using serial communication. The central electronic module (CEM) then activates the relay which supplies the wiper motor (6/1) with power in position 1. If high speed wiping is selected, the relay is also activated to power the motor in position 2.
The central electronic module (CEM) receives a signal from the motor when the wipers are in the parked position so that the wipers can be stopped in the correct position.
For intermittent wiping, the process is the same as for low speed, but the time between each stroke is set using the ring on the control stalk to one of eight positions between 1 and 27 seconds. The central electronic module (CEM) controls this once it has received information about intermittent wiping from the steering wheel module (SWM) via serial communication.
The windshield and headlamps are washed when the right-hand control stalk is moved towards the steering wheel. The steering wheel module (SWM) transmits information to the central electronic module (CEM) to activate washing via serial communication. The central electronic module (CEM) activates an internal relay which powers the pump motor (6/127) and the headlamp wiper motors (6/3-4) (S80 and R-models only).
For other models, the central electronic module (CEM) activates the relay (2/182) which powers high-pressure cleaning (6/104).
The central electronic module (CEM) receives a signal from the level sensor (7/5) in the windshield washer reservoir so that it can check the windshield washer reservoir level. The switch in the level sensor closes if the level falls below one liter. The central electronic module (CEM) sends the signal to Driver information module (DIM) (5/1) via the controller area network (CAN). The driver information module (DIM) displays a text message for approximately 10 seconds indicating that the windshield washer fluid needs to be topped up.
The tailgate wiper (6/32) (V70/XC70/XC90) is controlled by the rear electronic module (REM) (4/58). The rear electronic module (REM) receives a signal from the steering wheel module (SWM) via the central electronic module (CEM). The rear electronic module (REM) then powers the relay to start the tailgate wiper. The tailgate wiper is powered by the rear electronic module (REM).
The tailgate wiper can be programmed so that it is not activated if the windshield wipers are on and back-up (reverse) gear is selected.
Rear windshield cleaning is activated when the right-hand control stalk is pushed away from the steering wheel. The steering wheel module (SWM) transmits information to the central electronic module (CEM) to activate tailgate washing via serial communication. The central electronic module (CEM) activates the relay to power the pump motor (6/127). At the same time the rear electronic module (REM) activates the tailgate wiper.
The wipers only operate at low speed if there is a fault in the control area network (CAN). If this is the case, the central electronic module (CEM) receives a directly connected signal from the steering wheel module (SWM).
There is no Limp Home function for the rear windshield washer and wiper.