Troubleshooting in a Pick-to-Light system

Malfunctions in a Pick-to-Light system must be found and eliminated quickly. In this article, we explain the possible causes and the methods for eliminating faults.

Where can faults occur in a Pick-to-Light system?

A Pick-to-Light system consists of a control computer with host connection (usually a Windows server), controllers and Pick-to-Light displays. Of course, this also includes the cabling, terminals, mounting rails and extensions (such as scanners, scales, RFID).
You can find out more about the physical structure in the main article: Pick-to-Light & Pick-to-Light.

The system therefore consists of complex hardware and software components, which can also cause faults.

Basically, our system is very professionally developed, has been tried and tested for many years and is very stable. However, there are important prerequisites that must be met for trouble-free operation.

Wiring and the possible interference

The entire cabling below the controller is realised as a BUS. All compartment displays of a controller are connected in parallel and are directly addressed by the controller through addressing.

This makes the cabling very clear and basically unproblematic. It is of course possible to mix up the 4-core cables, but this is more a matter of installation or commissioning and not of productive operation.

Mechanical destruction is the most common cause of faults in the terminals and wiring.

When heavy order picking trolleys and racks are used, a collision can occur that causes the destruction. In that case, the defective cables and terminals must be replaced immediately.

Network connection and firewalls

In large installations, the on-site networks are often very complex. In some cases, several switches and even firewalls are in use. To ensure operation, the network parameters must be correct. So it is not enough to just check a ping to the controllers.

The changes or updates to the switches or firewalls are among the possible causes of malfunctions, which, however, occur very rarely in practice.

The elimination of these errors is one of the tasks of the on-site IT. According to the documentation, the appropriate ports and addresses must be set correctly.

Failure of the individual Pick-to-Light-subject displays

The compartment displays are very well protected and failures of the electronics are hardly known. With a zone test, all displays of a picking zone can be checked optically and electrically very quickly. The internal test mechanisms and error messages immediately register any irregularity.

Mechanical destruction of the displays is possible through the action of high forces.

The faults can be rectified by simply replacing the compartment displays.

Faults at the interfaces of the warehouse management

The Pick-to-Light system is usually supplied with data via various software interfaces (SAP via RFC, databases, TCP/IP sockets, REST, etc.). Some systems also function as stand-alone solutions and have no connections to the warehouse management software. We have also delivered Pick-to-Light systems where the complete information about the picking order was contained in a QR code.

The issue is of course, depending on the installation, very complex and not the same. Our system has several mechanisms to maintain a stable interface to the warehouse management (auto-connect mechanisms, data format checks, telegram repetitions, etc.).

The most frequent cause of malfunctions at the HOST interfaces is the incorrect master data and incorrectly implemented automation mechanisms after a restart of the systems.

We have a lot of experience with the development of interfaces and pay particular attention to the automation of the mechanisms in the event of a restart. Unfortunately, the customer's systems are often not prepared for such scenarios. The simulations during the commissioning and test phase of such exceptions is not possible in some cases (e.g. restart of SAP).

The problems with the master data are easy to find and also to fix. We have particularly well-developed log file systems for this purpose, where such errors can be found very quickly by our own technicians or the LUCA hotline. Our data transfer processes can also automatically identify and report some errors very quickly (e.g. incorrect warehouse compartment designations).

The emergency strategy

Even if all system components are very secure and professional, there is always a residual risk that an overall system will not function correctly.

For this reason, a contingency strategy for the possible failure of a picking system should always be created and tested during maintenance work. In some cases, these are simple paper picking lists to be printed by the warehouse management system.


The malfunctions of a Pick-to-Light system can have many causes and reasons. In order to find the faults as quickly as possible, professional LUCA training of the customer's personnel, up-to-date documentation and conclusion of LUCA hotline contracts are the basic prerequisites. The more important the plant is in the process chain, the shorter the response time and fault clearance must be. Nevertheless, emergency strategies in the event of a total breakdown are also very important and crucial to us.
More about order picking: What is order picking?

Many years of experience in paperless order picking