Current Limiting Volvo XC70 I facelift

Current Limiting

The central electronic module (CEM) checks and sometimes limits the current from the battery and generator.

The central electronic module (CEM) communicates with the alternator control module (ACM) via serial communication.

If there is a fault with current limitation, the general warning lamp will light in the driver information module (DIM) and a text message will be displayed.

Scheme 201

The steering wheel module (SWM) has the task of managing the signals for those functions which can be controlled via the steering wheel control stalks and buttons. The signals are transmitted using LIN communication to the central electronic module (CEM). The central electronic module (CEM) forwards these signals on the controller area network (CAN) to the relevant control modules. The actual functions are not in the steering wheel module (SWM).

The steering wheel module (SWM) manages the control signals for the following functions

1. Volume control and CD track / radio selection
2. Volume control during hands free carphone calls and menu selection for the phone module (PHM)
3. Menu selection for traffic information
4. Front windshield wipers and washers
5. Rear windshield wiper and washer (V70, XC70 and XC90)
6. Cruise control
7. Turn signal lamps
8. High and low beam
9. Trip computer and displaying/erasing text messages in the driver information module (DIM).

The steering wheel module (SWM) is integrated into the steering wheel bracket. The steering wheel must be removed to replace the steering wheel module (SWM). Control stalks, key pads and switches can be replaced as separate units.

Cars with DSTC also have a steering wheel angle sensor in the contact reel in the steering wheel module (SWM). For further information, see Design and Function, Steering wheel angle sensor module (SAS).

A simple way to ensure that the steering wheel module (SWM) is powered and grounded is to flash the headlamp high beam or to change the audio or carphone volume.

Scheme 202

The steering wheel buttons control functions and menu selection for

1. Traffic information (option)
2. Audio (option)
3. Carphone (option)
4. Cruise control (option).

The signals from the steering wheel buttons are transmitted via serial communication.

Scheme 203

The headlamps are operated via the light switch module (LSM). This is on the dashboard at the side of the steering wheel. The light switch module (LSM) uses serial communication to communicate with the central electronic module (CEM). Low and high beam are operated by moving the left-hand control stalk towards the steering wheel.

Low beam is powered directly by the central electronic module (CEM). High beam is powered via a directly connected relay in the central electronic module (CEM). The level of the supply voltage to the low beam is regulated by the central electronic module (CEM). When the supply voltage is sufficient (in excess of 13 V), pulse width modulation is used to maintain the voltage level at 13.0 V +/- 0.2 V. This does not apply to cars with Bi-Xenon lamps.

Cars with Bi-Xenon lamps are powered directly via the central electronic module (CEM) without pulse width modulation.

In Bi-Xenon lamps, the reflector in the lamp housing is moved by an actuator motor when changing between high and low beam. The actuator motor is integrated in the lamp housing.

To detect problems with the low beam, the central electronic module (CEM) reads the power consumption of the circuit. If this falls below a certain threshold value a fault will be indicated. The general warning lamp lights in the driver information module (DIM) and a text message is displayed.

There are also diagnostics for the high and low beam function (actuator motor) for Bi-Xenon lamps.

For further information about Bi-Xenon lamps, see Design and Function, Gas discharge lamps (GDL).

Scheme 204

There are two motors, one on each headlamp, which angle the headlamps upwards or downwards to control the range of the beam. The motors are on the rear of the headlamps.

The motors are controlled by a thumb wheel which is located in the light switch module (LSM) on the dashboard by the side of the steering wheel.

If the thumb wheel is turned, information is transmitted to the motors which adjust the headlamps accordingly.

There are diagnostics for the headlamp range adjustment.