Vehicle level sensor – Design, function and troubleshooting

HELLA TECH WORLD – The workshop's friend

The vehicle level sensor is a central component for monitoring the vehicle height. The sensor measures the vertical position of the vehicle body relative to the axle or chassis. Its measurement data forms the basis for numerous vehicle systems such as the automatic headlamp levelling system, adaptive chassis systems and various stability and comfort functions.

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 use by suitably qualified personnel only.

Design and function principle of the vehicle level sensor

Vehicle level sensors are angular position sensors that are attached directly to chassis and body parts. They consist of a sensor housing that is firmly connected to the body or axle beam via a bracket, and a lever arm that is attached, for example, to the transverse control arm. The lever arm can have different lengths and methods of connection, depending on the vehicle version.

If the position between the moving chassis parts and the vehicle body or axle beam changes, the lever arm moves accordingly. It transmits this movement directly to the sensor, where it is converted into a rotary movement. The sensor converts this rotary movement into an electrical signal and sends it to the higher-level control unit. In this way, changes in ride height can be precisely detected and used to control chassis and comfort systems.

As vehicle level sensors are also used in safety-relevant systems, a particularly high level of reliability is required. That is why redundant sensors are often used. Two independent measuring channels then work in parallel. Both channels detect the same movement and each sends a signal to the higher-level control unit. If the two signal values differ from each other, the control unit detects an irregularity and can react appropriately. In this way, a possible failure is detected in good time and the functional safety of the overall system is ensured.

Sensor types frequently used in practice are:

Potentiometric sensors

This type determines the position via a variable resistor. Such sensors are often found in older vehicles or simple levelling systems. The disadvantage is the wear of the sliding contacts inside the sensor that can be worn out by the constant mechanical movement.

Inductive sensors

Inductive sensors detect movements via electromagnetic induction. The measuring principle requires no moving contacts, making the sensors robust, durable and precise. Inductive sensors are often used in systems with air suspension or in adaptive chassis.

The CIPOS® (Contactless Inductive Position Sensor) technology developed by HELLA is a special type of inductive sensor. It combines the advantages of induction with specially developed electronics and guarantees reliable operation even under the loads typically encountered in vehicles.

Typical properties:

Contactless and wear-free
Insensitive to magnetic fields
High temperature stability
Robust against vibrations, moisture and dirt
Multi-channel structure for redundant measurements

Hall effect sensors

These sensors use a magnetic field that changes with movement. These sensors also have no moving contacts. Hall sensors are low-maintenance and reliable. Typical areas of application are modern vehicles with xenon or LED headlamps that require automatic headlamp levelling.

Areas of application

Vehicle level sensors are used in various vehicle systems:

Application	Objective	Systems involved
Automatic headlamp levelling	Glare-free light pattern	Level sensor + headlight control unit
Air suspension	Constant ground clearance	Level sensor + air suspension control unit
Dynamic chassis control	Comfort and driving stability	Level sensor + damper control
Trailer operation	Stable vehicle level and glare-free light when loaded	Level sensor + automatic headlamp levelling or level control

Furthermore, angular position sensors can also be used in other areas, for example in agricultural vehicles or construction machinery. They are used there, for example, to detect the flap position on trailers or the bucket position on construction machinery.

Causes of failure and symptoms

Vehicle level sensors are installed in the area of the chassis and are therefore subjected to different loads throughout the vehicle's service life. Typical causes of malfunctions or failure are:

Mechanical damage: Defective or bent lever arms, for example due to stones, collisions or improper installation.
Electrical faults: Broken cables, corrosion on plug connections or short circuits due to moisture. Internal malfunctions in the integrated circuit can also lead to faulty signals or a failure.
Environmental influences: Ingress of water, salt or dirt can damage the seals and the housing.
Wear on potentiometers: Wear of the resistor track due to continuous operation in older, mechanically operating sensors.

Possible symptoms:

A warning lamp lights up in the instrument cluster
Driver information or error messages relating to driver assistance or chassis systems
Fault in or failure of the automatic headlamp levelling system
Unusual driving behaviour with adaptive chassis (e.g. too hard or too soft)
Activation of an emergency running programme in the control unit

Exemplary representation of the control unit diagnostics

The function of the vehicle level sensor is monitored by the higher-level control unit. During diagnostics, not only can the fault memory be read out but also additional functions such as parameter queries or circuit diagrams can be displayed, depending on the vehicle type. Basic settings in relation to the vehicle height may also be available, again depending on the vehicle type and configuration.

Exemplary representation of the fault memory query

Exemplary representation of driver information in the instrument cluster

Read out the fault memory

This function allows the error codes stored in the control unit to be read out and deleted. The codes provide information on whether there are faults in the vehicle level sensor itself, in the wiring or in the communication with the control unit.

The following error code is stored in our case example:

Error code 49 / C103715

Fault detected
Driver information in the vehicle: Air spring: Fault! Please visit Service

Exemplary representation of the parameter query - Sensor value rear right not OK

Exemplary representation of the parameter query - Sensor value rear right OK

Parameters

Current values of the vehicle level sensor can be displayed in this function. These include, for example, the determined height deviation from the standard position (reference height of the vehicle) or the determined vehicle height (absolute). These values are useful for being able to assess the behaviour of the sensor during operation and detecting deviations.

This allows you to check whether the signals from the left and right level sensors match or whether there are implausible values that indicate an electrical or mechanical defect.

Exemplary representation of the basic setting - relearning the control position

Basic settings

After working on sensors in the chassis area or after replacing chassis components, it may be necessary to re-learn the control position. This is the reference height to which the control unit refers when controlling the chassis. The control unit adopts the current ride heights at all four wheels as target values.

The following problems may occur if the control position has not been taught correctly:

Incorrect vehicle height (e.g. higher or lower on one side)
Error messages in the instrument cluster
Malfunctions in the automatic levelling system
Impaired driving dynamics or comfort

Depending on the vehicle type and configuration, programming is carried out via the basic settings in the diagnostic unit.

Exemplary representation of a circuit diagram - integration of the vehicle level sensors into the vehicle electrical system. 1. Chassis control unit 2. Vehicle level sensor front right 3. Vehicle level sensor rear left 4. Vehicle level sensor rear right 5. Vehicle level sensor front left

Circuit diagrams

System-specific circuit diagrams can be taken from the vehicle information and used for troubleshooting. They show the electrical connection of the vehicle level sensors and their integration into the vehicle electrical system.

In this way, signal paths between the control unit and sensors can be traced and possible interruptions or malfunctions can be localised. Especially with complex chassis or lighting systems, working with circuit diagrams is an important aid to localising sources of faults quickly and reliably.

Maintenance and repair instructions

The vehicle level sensor should only be installed and removed by trained specialists.
Before installation, ensure that the sensor is suitable for the intended application and that it has the required dimensions, connections and properties.
After installation, the chassis height should be checked using a suitable diagnostic device. Check that the control position is correctly recognised and that the sensor signals are plausible. Then delete the fault memory.
Depending on the vehicle type and the work carried out, it may be necessary to recalibrate the control position of the vehicle so that the current ride heights are adopted as reference values. It may also be necessary to calibrate vehicle-specific assistance systems. The ADAS CSC tool from HELLA Gutmann that can be used to precisely calibrate driver assistance systems from different manufacturers is ideal for this work.
The removal, installation and safety instructions of the respective vehicle manufacturer must be observed in this context.
HELLA accepts no liability for damage caused by improper handling or incorrect installation.
Country-specific regulations on occupational safety, accident prevention and disposal must be observed.

The various diagnostic options have been illustrated as examples using the mega macs X diagnostic unit. The respective test depth and variety of functions can differ from vehicle manufacturer to vehicle manufacturer and depend on the respective system configuration of the control unit. Exemplary representations, pictures and descriptions serve to explain and illustrate the document text and cannot be used as a basis for vehicle-specific repairs.

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