A 2016 vehicle rolled into a German workshop with a single symptom written on the job card: “RDKS leuchtet”. When the technician plugged in the OBD reader, the system returned just one fault code, B124D. We see this scenario frequently in our Wrenchlane platform data, especially around seasonal tire changeover periods. Customers often assume a warning light on the dash means a simple top-up of air is required, but the underlying system complexity usually tells a different story. By looking at how our diagnostic engine ranked the historical repair data and specific causes for this exact fault code, we can map out exactly how to tackle this problem in the bay without relying on guesswork.
The Dominant Cause: Overlooking the Relearn Procedure
When we process B124D across our platform, the highest probability cause, ranked at 82 percent with a low severity, is a missing TPMS relearn or reset sequence following a wheel change. Whether a vehicle is getting a seasonal swap to winter wheels or just a routine tire rotation from front to back, the Body Control Module (BCM) expects to see familiar sensor IDs at specific corners of the chassis.
The BCM constantly monitors the cyclic signal reception from all four TPMS sensors, which transmit at 433.92 MHz in the European market. If a technician swaps the wheels but does not perform a manual pressure reset or trigger the required relearn sequence for the new sensor IDs, the BCM eventually flags a problem. The system allows a certain grace period, but after a defined driving cycle (usually 15 to 20 minutes at sustained speeds above 20 km/h), the module realizes the known IDs are missing from the data stream. It interprets this absence as a general signal failure and immediately sets the B124D fault code.
To confirm this is your root cause, you should start by performing a standard tire pressure reset through the dashboard menu in the instrument cluster. If that does not clear the fault, activate the TPMS relearn mode and sequentially trigger all four wheel positions using your diagnostic tool. Finally, read the live data in the BCM to verify that the newly registered sensor IDs perfectly match what is actually broadcasting from the wheels.
Mechanical Sensor Damage from Tire Machines
If the software relearn procedure fails to resolve the warning light, the next most probable cause in our diagnostic data sits at a 75 percent likelihood with a medium severity rating. This is mechanical damage to a TPMS sensor, a failure that almost always occurs directly on the tire mounting machine during a previous visit.
When changing tires on existing rims, the sensor is highly vulnerable to both the bead breaker shoe and the mounting head. If a technician positions the bead breaker directly at the valve stem, or if the tire bead is pried over the mounting head incorrectly, the physical stress is transferred straight into the fragile plastic sensor body. The housing can crack, or worse, the internal high-frequency transmitting antenna gets torn completely off the circuit board. The physically damaged sensor goes completely silent, sending zero radio telegrams to the receiver module. This communication blackout directly sets a B124D fault.
Testing for physical damage requires a handheld TPMS testing tool. Query the high-frequency signal of each individual wheel at the valve stem. If one corner fails to respond to the ping, perform a close visual inspection of the valve stem itself, looking for unnatural bends or hairline cracks in the metal. To be absolutely certain, you will need to deflate the tire, break the bead on the affected wheel, and physically inspect the sensor body inside the rim cavity.
Reaching the Battery Age Limit
Vehicles built in 2016 are currently sitting right at the end of a very specific hardware lifespan. Our diagnostic engine ranks a depleted internal sensor battery as the third most likely cause for this code, sitting at 65 percent with a medium severity rating.
Original equipment TPMS sensors rely on integrated lithium cells that cannot be replaced separately from the sensor body. These batteries have a typical design life of 5 to 8 years. Because this is a 2016 vehicle, the original batteries are hitting their absolute limit. A sudden drop in tire pressure during a swap, a sharp decrease in ambient workshop temperature, or simply waking up the sensor after a long period of summer storage can cause the cell voltage to drop abruptly. If the voltage dips below the minimum operating threshold of approximately 2.6 volts, the sensor shuts down entirely. It stops transmitting its data telegram to the BCM, triggering the exact same B124D code.
You can verify this without taking the vehicle off the ground. Use a TPMS handheld tester to read the internal battery state of all four sensors. Additionally, check the BCM data stream on your diagnostic scanner for transmission delays or specific battery error flags. If one battery has failed due to age, the other three are generally not far behind.
Incompatible or Unprogrammed Sensor Hardware
Ranked at 50 percent probability, also with a medium severity, is the presence of incompatible, unprogrammed, or entirely missing TPMS sensors. This issue spikes noticeably when customers bolt on a different set of wheels for the winter season or upgrade to aftermarket alloy rims.
Often, these secondary wheel sets are fitted with universal programmable sensors. If the installer forgot to flash these universal blanks with the correct vehicle protocol, the BCM will not understand the incoming data structure. Furthermore, some incorrectly sourced sensors transmit at the US standard frequency of 315 MHz rather than the European mandated 433.92 MHz. The antenna simply cannot hear them. In the most extreme cases, standard rubber pull-through valves without any sensor electronics whatsoever might have been installed on cheap steel wheels. The BCM hears nothing compatible and logs the fault.
Begin with a basic visual check of the valve types on the vehicle. Look for the telltale signs of a sensor, such as a rigid metal collar or a specific thick TPMS-style rubber stem. Then, use a universal TPMS programming device to check the broadcasting frequency and verify the programmed protocol of every single wheel.
Applying This to Your Bay Workflow
When a vehicle comes in with a B124D code and an illuminated TPMS light, jumping straight to taking tires off rims is an unnecessary risk. Start with the software reset and relearn, check the battery voltages and broadcast frequencies with a handheld tool, and consider the sheer age of the vehicle before you break a single bead. Have you noticed a spike in these specific communication codes in your own workshop right after the seasonal tire rush? Check your diagnostic logs and see if these exact patterns are slowing down your bays.
