UN ECE R141 compliance: Mandatory tyre pressure systems and the consequences for drivers and operators.
From 6 July 2024, all new trailers in the EU must be equipped with a tyre pressure monitoring system that supports a warning light in the dashboard of the truck. This legislation, UN ECE R-141, increases road safety for all road users, saves fuel costs and increases the lifetime of trailer tyres.
Every STAS trailer will be equipped with one of the following systems:
- The (now standard) Tyre Pressure Monitoring System (TPMS) with sensors strapped around the rims inside the tyres;
- A Tyre Pressure Refill System (TPRS) that automatically keeps the trailer tyres at the right pressure.
Both of these systems have been available at STAS for a few years now. However, UN ECE R141 legislation now requires truck and trailer manufacturers to also support a non-proprietary warning signal between the truck and the trailer, and not only through the Smartboard or with a warning light on the trailer.
This means that all trucks will show the warning signal from any trailer in the dashboard or infotainment system, if both truck and trailer were registered after July the 6th 2024.
Of course, there are a few practical questions that arise from this change in legislation. Because the consequences are a little bit different between the TPMS system and the TPRS system, we answer questions about these systems separately:
UN ECE R141 compliant TPMS (Tyre Pressure Monitoring System)
What is TPMS and how does it work?
TPMS stands for Tire Pressure Monitoring System. Each wheel, including the spare, has a sensor with a battery that monitors air pressure and temperature inside the tyre. These sensors send data to the Trailer EBS system, which relays the warning to the truck via the CAN connection.
How long do the sensors last?
The sensor batteries typically last between 5 to 10 years. Battery status can be checked by your STAS dealer and a battery warning will be shown approximately six months before the batteries needs to be replaced, ensuring enough time to replace them.
What does the warning look like in the truck?
It varies by truck. Some show which wheel has an issue, while others just display a TPMS warning light in orange or red. Older trucks might not show any warning if they don’t support TPMS communication over the CAN bus.
When does the warning get triggered?
The warning gets triggered at a pressure loss of 0,2 bar. Minor pressure loss over time or low temperatures can trigger the warning. If the warning persists after reinflation, check for a small hole or a leaking valve using soapy water.
What should the driver do when the TPMS warning comes on?
The warning could mean a pressure loss of 0.2 bar or more or that the wheel is overheating. The driver should check the tires, brakes, and rims. If there's visible damage or uncertainty, they should replace the tire or call for help.
Click here for a guide for checking the tires.
What if the warning light stays on after changing or refilling a tire?
Turn off the ignition for five seconds and try again to reset the system. It might take a few minutes for the sensors to update their status. If the warning persists, check the tires, brakes and rims. If there's visible damage or uncertainty, they should replace the tire or call for help.
Do you need to reprogram the system every time you change the wheel positions?
Yes, the wheel positions are programmed into the system, so you’ll need to update them whenever you change a wheel position.
Do the spare wheels from STAS come with the TPMS sensors?
Yes, so dealers and service points can update wheel positions without having to remove the tire from the rim.
UN ECE R141 compliant TPRS (Tyre Pressure Refill System)
What is TPRS and how does it work?
TPRS stands for Tyre Pressure Refill System, and the system does exactly that: refilling the tyres when needed. Each tire valve connects to the center of the axle body which is pressurized with a step-up valve that keeps air pressure at 9 bar. The pressure sensor for the warning in the truck is mounted in the step-up valve, so there’s no need for reprogramming when changing wheel positions.
What does the warning look like in the truck?
It depends on the truck. The warning could be an orange or red light, text, or schematic on the dashboard or infotainment system. If the system refills a tire, the warning goes away. If a tire is severely damaged, the warning stays on. Like in the past, STAS will still fit the warning light on the side underrun protection to accommodate older truck models that don’t yet support the warning signal from the trailer.
When does the warning get triggered?
Whenever the TPRS system activates, a warning will be shown. Momentary warnings can happen due to pressure loss or cold temperatures. Persistent warnings mean a problem that needs immediate attention.
What should the driver do when the warning comes on?
If the warning disappears quickly, check the tires at the next stop. If it stays on, stop immediately to inspect the tires.
