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For over a year now, the Xenon headlights of my 2006 VOLVO V70 II 2.4 D, 163 PS, Xenon, are permanently in lowest position and computer tells me "headlights defect, service required" +VOLVO read the code "voltage too low" for BOTH healights. When switching on headlights (or even only parking lights!) both range control motors raise headlights' beam first to highest, then, in the next second, to lowest position ("safe mode"). Odd thing is, I had VOLVO confirm there is actually no issue with either the Xenon bulbs, rear axle levelling sensor, range control motors, or the cabels in between. All components except central - and rear electronic module (CEM & REM) have been replaced, to no effect, the error persists!
To cut a long story short, I have nothing but a vague guess from VOLVO that either the CEM or REM is faulty. No way to replace these ridiculously expensive components unless I know for sure what's wrong...

Does anyone have some idea what might be at the bottom of this problem? Some guys pointed out to me the FRONT levelling sensor might be faulty, but a can't find a sensor connected to the front strut-arms. Does anyone know for sure if a FRONT sensor is fitted to this model at all? Please note German law requires automatic headlight range control for all xenon-headlights, so this might differ to US-built models.

This is a short translation of a much longer story which I posted on several German sites. More information is available on request.

Thanks & Best!
Holger
 

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This is the VIDA description. I don't know if you have 4-C suspension or not, suspect that you don't. But this tells the function of the various items, and you can see there is only 1 sensor on the rear suspension, and both the REM and the CEM have a role if you don't have 4-C suspension. I wonder if your dealer even bothered to test the voltage of the sensor?

From VIDA for 2006 V70 2.4 D
Sensor
The following applies to cars without Four-C (Continuously Controlled Chassis Concept)
An inductive position sensor reads the angle between the body and the left rear control arm. The angle is a indication of how much the vehicle is leaning (chassis height) and depends on weight distribution.

The sensor is mounted slightly differently for FWD and AWD.
The rear electronic module (REM) reads off an analog signal (0.5 - 4.5 V) from the position sensor and converts it to an angle value (±35°), which is sent to the central electronic module (CEM).
A fully loaded vehicle generates a signal of 0.5 V, which corresponds to negative 35°.
The central electronic module (CEM) regulates the headlight levelling motors (PWM signal) to adjust the headlights vertically.


The following applies to vehicles with Four-C
Two sensors read the angle between the body and the left and right rear control arm. The angle is a indication of how much the vehicle is leaning (chassis height) and depends on weight distribution.
The sensors are mounted slightly differently for FWD and AWD.
The suspension module (SUM) reads off the signals from the sensors and converts them to an angle value. The value is sent to the central electronic module (CEM) via the CAN network. The central electronic module (CEM) uses the information to regulate the headlight levelling motors.



Level control
Regulation at speeds below 4 km/h (2.5 mph)
When the ignition is switched on, the position sensor is read and the headlight levelling motors adjust the headlights.
Regulation at speeds above 4 km/h (2.5 mph)
The headlights are regulated if there are great angle changes while driving. Regulation is time-dependant so that the system does not react to short changes, such as unevenness in the road surface.



Calibration
The position sensor must be calibrated after work on the rear suspension. Perform calibration as described in the tab DIAGNOSTICS/VEHICLE COMMUNICATION, Rear electronic module (REM).
did your dealer do this?

Caution! Calibration must be carried out after work such as removing/installing the sensors and replacing the sensors, rear axle, bushings, shock absorbers or springs. In vehicles with Four C, calibration is carried out via the suspension module (SUM). Beam adjustment is carried out conventionally (via adjustment screws by the headlight). The light switch must be in the "on" position while calibrating.
Safety
In the event of a short-circuit on the high voltage side, the power supply is cut off for less than 10 ms.
If the high voltage circuit is broken (such as due to an open circuit, defective bulb or no bulb in the lamp socket), during each activation the system attempts to light the lamp for a period of 700 ms. During the period, there is high voltage across the ballast.
Approximate component temperatures during operation: Ballast = 130 °C (266 °F), Bulb holder = 170 °C (338 °F), Bulb = 400 °C (752 °F).
The glass body of the Bi-Xenon lamp is filled with various gases and metal vapors and is under pressure. Because the lamp is subjected to gas pressure, it could explode.
Warning! Follow the safety instructions and recommendations in VIDA carefully when working with high voltage. Use safety goggles when handling the bulb. Risk of explosion! The electrical system must be switched off before starting work. Risk of burn injury. The components operate at very high temperatures.
 
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