Headlamp levelling system

Here you can find useful tips on the topic of vehicle headlamp levelling systems.

The load condition and pitching motion of the vehicle change the illumination range of the headlamps. This may dazzle other road users. This is why headlamp levelling systems (HLS) are legally prescribed. On this page, find out how standard market systems work, and how you can check them with simple means. Here, you can also learn what to do in the event of malfunction, and what you should note when adjusting headlamps with an automatic HLS.

Important safety note
The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their day-to-day work. The information provided on this website is intended for suitably qualified personnel only.

MANUAL HEADLAMP LEVELLING SYSTEMS: FUNCTION

A headlamp levelling system adjusts the height of the cut-off line to the load condition of the vehicle. This is supposed to avoid blinding oncoming traffic when the vehicle is loaded. Manual and automatic headlamp levelling systems are installed in current vehicle models. With manual systems, drivers have to adjust the inclination of the headlamp themselves by means of a switch. There are pneumatically and electrically operated systems.

 

The problem with this is that many loaded vehicles dazzle oncoming traffic since drivers are not well informed enough about the adjustment possibilities and their function on their vehicle.

AUTOMATIC HEADLAMP LEVELLING SYSTEMS: FUNCTION

Design of an automatic HLS

These headlamp levelling systems fulfil their task without driver activity. We differentiate between two systems: Semi-static and dynamic headlamp levelling.

Automatic headlamp levelling systems: Design

1 Headlamp, 2 Actuator, 3 Front axle sensor, 4 Light switch, 5 Control unit, 6 Rear axle sensor, 7 RPM sensor, 8 Load

Semi-static headlamp levelling system

For the automatic headlamp levelling systems, we differentiate between two systems: Semi-static and dynamic headlamp levelling systems. The semi-static headlamp levelling system only corrects changes in headlamp inclination due to changes in load status.

 

A control unit evaluates the data from the front and rear axle sensors, compares this with the stored nominal data and triggers the actuator motors on the headlamps accordingly.

Usually the same type of actuator motors are used as for manual headlamp levelling systems. In the case of compact vehicles without long wheel overhang, this system offers the possibility of doing without the front axle sensor since the changes in inclination mainly occur on the rear axle only. In addition, semi-static headlamp levelling works with great damping, i.e. it only makes adjustments when the body is inclined for prolonged periods. In HELLA's xenon conversion sets an ultrasound system is used. Here, the sensor measures the direct distance to the road.

Dynamic headlamp levelling systems

Today, almost all the vehicles fitted with xenon headlights are equipped with dynamic headlamp levelling systems which also react to driving-related changes in inclination, such as acceleration and braking.

The block diagram shows the design of a dynamic headlamp levelling system. The control unit calculates the nominal data on the basis of the sensor data, taking the driving conditions into account. In contrast to semi-static headlamp leveling systems, the actuator motors are then triggered within fractions of a second. To make these quick response times possible, stepper motors are mainly used as actuators on the headlamps.

TIPS FOR DEALING WITH HEADLAMP LEVELLING SYSTEMS: PRACTICAL TIPS

If there is an electrical fault in the headlamp levelling system during driving, the headlamps remain in this position. In other vehicles, though, the headlamps are moved to the home position and stay there. The driver is always alerted about the error by a signal light or a text message in the cockpit.

DEFECTIVE HEADLAMP LEVELLING SYSTEM: CAUSE OF FAILURE

  • Actuator motors on the headlamps are faulty
  • Headlamp levelling system sensor for vehicle level is faulty
  • Control unit has been replaced and not coded
  • Headlamps have not been adjusted (basic setting)
  • Control unit faulty
  • Interrupted data cable
  • No supply voltage
  • Mechanical damage

CHECKING HEADLAMP LEVELLING SYSTEMS: TROUBLESHOOTING

To adjust the headlamps a diagnostics tester is generally required for an automatic HLS. This can also be used to carry out diagnostics on the headlamp levelling system.

 

The headlamp levelling system can be inspected without a diagnostics tester, however, with the aid of a multimeter and oscilloscope. It is important, however, to always make sure that a circuit diagram of the system to be tested is available.

Function check

  • Place the unloaded vehicle on an even surface.
  • Align the beamsetter in front of the car and switch the low beam on. Check the correct cut-off line.
  • Add a load to the rear end of the vehicle, e.g. by loading the trunk. With semi-static headlamp levelling, headlamp adjustment takes place after a few seconds and can be followed on the beamsetter. In the case of dynamic headlamp levelling, adjustment takes place extremely quickly, so that in the case of some vehicles the adjustment process is only perceived as a brief "flash" on the beamsetter test screen. For some vehicles, this adjustment happens only during driving, though.

If no adjustment process can be perceived, the following measurements should be carried out

  • Check voltage supply to the actuator motors, the control unit, and the headlamp levelling system sensor.
  • Check the headlamp levelling system sensor and data cable for mechanical damage and check correct installation position.
  • Use the oscilloscope to check the sensor signal.
  • Use a diagnostics tester to check the parameters and actual values.

ADJUSTING XENON HEADLIGHT LEVELLING SYSTEMS: VIDEO

Adjustment/Diagnostics of xenon headlights with automatic headlamp levelling systems

Carrying out of diagnostics with subsequent adjustment of a xenon headlight with automatic headlamp levelling system.

COMPULSORY HEADLAMP LEVELLING SYSTEMS: REGULATIONS

Since 1993, new vehicles have been legally required to have a headlamp levelling system. The regulations can be found in the directives 76/756/EEC and ECE-R48.

How helpful is this article for you?

Not helpful at all

Very helpful

Please tell us what you did not like.
Many thanks. But before you go.

Sign up for our free HELLA TECH WORLD newsletter to receive the latest technical videos, car repair advice, training course information, marketing campaign details and diagnostic tips.

Show additional information on our newsletter Hide additional information on our newsletter

Register for our free HELLA TECH WORLD newsletter to stay up-to-date with the latest technical videos, car repair advice, trainings, diagnostic tips and marketing campaigns.

Together we can get cars back on the road quickly!

Please note:
You will only be subscribed to the newsletter once you have clicked on the confirmation link in the notification e-mail you will receive shortly!

Data Protection | Unsubscribe

Please note:
You will only be subscribed to the newsletter once you have clicked on the confirmation link in the notification e-mail you will receive shortly!

Data Protection | Unsubscribe

Almost there!

All you need to do is confirm your sign up!
We've sent an e-mail to your email address.

Check your inbox and click on the confirmation link to start receiving HELLA TECH WORLD updates.

Wrong e-mail or no confirmation received?
Click here to enter it again.