In today’s article I’ll cover the following:
- What is TPMS and how does it work
- The system components overview
- How to enable/disable TPMS (coding)
- How to retrofit tire pressure monitor system
- Much more…
What is a Tire Pressure Monitor System (TPMS)?
The system monitors the tire pressure and alerts the driver when to correct the tire pressure. Depending on the BMW model, the tire pressure readings are displayed in the instrument cluster (non-iDrive vehicles) or via a central information display (iDrive equipped vehicles).
To meet legislative requirements in most markets, every vehicle must be equipped with a TPM system. It is available as an option in other markets.
Why Is Tire Pressure Important?
A drop in tire pressure can cause various damages to the tire. When tire pressure is lost on one or more wheels, the tire pressure indicator alerts the driver. This can also help to avoid tire damage before it happens.
Besides the tire wear and damage, the low tire pressure also affects the vehicle’s stability and driveability.
TPMS System Overview
|1||Wheel sensor, front left||2||Wheel sensor, front right|
|3||Wheel sensor, rear right||4||Wheel sensor, rear left|
|5||Remote control receiver|
How Does TPMS Work?
The Dynamic Stability Control (DSC) control unit has a built-in tire pressure control feature.
The radio signals from the wheel electronics are received by the remote control receiver. The CAN bus connects the remote control receiver to the Body Domain Controller (BDC). The signals are forwarded to the DSC control unit via the bus connection by the Body Domain Controller (BDC).
The messages sent by the wheel sensors are processed by the DSC control unit. Each of the wheel sensors sends the following information above a speed of about 15 mph:
- Tire pressure
- Tire air temperature
- The remaining service life of the battery
- Data from the impact sensor and Identification Feature (ID) of the wheel sensors
- Transmission mode
|1||DSC control unit||2||Hydraulic unit|
The instrument cluster and head unit receive data from the DSC control unit.
A warning and indicator light on the instrument cluster shows a tire pressure drop, and a Check Control message is displayed.
The iDrive head unit’s central information display can be utilized to get more information about the tire pressure by looking at the vehicle status.
The tire pressure monitoring system must also be initialized using the head unit.
Electronics for the wheels
Wheel electronics systems are fitted in the wheel drop center of all wheels. The filling valves are bolted to the wheel electronics systems (made of metal). All-wheel electronics systems are made up of the same components. The acceptable working temperature ranges from -40°C to +125°C. The actual temperature in the tire is monitored by the wheel electronics. When the temperature rises over roughly 115°C, the tire pressure management goes into a limited-function mode. The hardware is turned off in specific instances.
An acceleration sensor is built into each wheel electronics unit. Whether the wheel is stationary or rotating is detected by the acceleration sensor.
The remote receiver does not provide messages to the Dynamic Stability Control when the wheels are stationary (DSC). The wheel electronics are in a state of inactivity. The battery life of the wheel electronics is extended as a result of this.
The wheel electronics go into “standby” mode once the vehicle reaches 30 km/h (18 mph). The wheel electronics begin transmitting in predetermined cycles.
At regular intervals, the wheel electronics measure the tire inflation pressure and temperature. In periodic cycles, the remote receiver transfers this monitored data from the tire to the DSC.
|1||Wheel sensor (electronics)||2||Transmission frequency|
A lithium-ion battery provides power to the wheel sensor. The service life is expected to be about ten years. The remaining service life is presented with a month-accurate prediction.
Assigning The Wheels
The assignment of the wheels in the DSC may necessitate a drive of up to 9 minutes.
The wheel electronics are in “learning” mode during the wheel assignment identification procedure.
Centrifugal force is created as a wheel rotates. At a speed of about 15 mph, the impact sensor begins to register this centrifugal force. The impact sensor uses the acceleration of the earth to determine the position of the wheel electronics.
The “learning” mode requires this position (12 o’clock).
The DSC control unit reassigns the positions of the four wheels in learning mode. Adjusting the position assignment between the wheel electronics and the wheel speed sensors accomplishes this.
Receiver for remote control
The wheel sensors’ messages are sent to the remote control receiver through a high-frequency transmission channel (433 MHz). Every 15-30 seconds, communication to the remote control receiver is sent. The Body Domain Controller receives the current status of the messages via the LIN bus (BDC/FEM). The messages are sent from the BDC or FEM control unit to the DSC control unit via the FlexRay bus. The messages are evaluated by the DSC control unit.
|1||Remote control receiver||2||three‐pin plug connection|
Examine the aluminum screw valve to see if wheel TPMS valves have been installed. The vehicles without TPMS have black rubber valves. The fault memory entry can be used to determine whether the correct wheel electronics were installed or whether there was a mixed installation by various manufacturers. The RDC tool can be used to find out who made the wheel electronics.
TPMS Sensor Initialization
Following a tire or wheel change, a 5-minute stationary period is required before the tire pressure monitor can be initialized.
In the following situations, the tire pressure control must be initialized:
- When you change the tire pressure.
- When the wheels are replaced. Wheels that have been switched must have the appropriate wheel electronics systems installed.
- The vehicle’s wheels are exchanged axle-by-axle.
The existing inflation pressure is conveyed as a specification for the nominal pressure during the initialization procedure.
Setting The Tire Pressure
On cold tyres, the driver is individually responsible for setting the proper inflation pressures according to the operating instructions. According to the model series, the initialization procedure can be managed from several locations. The iDrive
To find the recommended tire pressure check the sticker on the inside edge of the driver’s door.
TPMS Delete Coding
If you want to disable the TPMS system in your BMW, the simple VO coding will be enough.
Just remove 2VB from the vehicle order and code DSC, ICM, KOMBI, and iDrive Head Unit module.
Now you’ll still have the FTM (Flat Tire Monitor) system active.
Don’t forget to unplug the TPMS control unit! It makes no difference whether you’ll unplug it before or after the coding.
It is impossible to write a TPMS retrofit guide that will fit all BMW models, so while you can follow this guide you also need to acquire the correct parts for your BMW model. The parts are different for various markets, vehicle production dates, and of course the models.
The most important thing is that the TPMS (RDC) control unit matches the wheel sensors (it depends on the production date and different transmitting frequencies used across markets).
This is the example of a 2014 BMW 3-Series F30 and it is very similar across all model ranges.
- RDC (TPMS) Control Unit
- TPMS control unit bracket and nuts
- Wiring (Can’t be bought, you must DIY)
- 4x wheel sensors (complete with valves and electronics)
To find the correct part, you should use the BMW parts catalog, like ETK or RealOEM.
TPMS wiring (BMW F30 example)
The power supply (pin 2) goes to the rear fuse holder. It doesn’t have to be an F132 fuse, but it has to be a 30B terminal.
The CAN bus (Pins 1&3) can be connected anywhere on the K_CAN bus (K=Karoserie/Body). In the case of the F30, the K_CAN goes to/from the FEM module. If the car is already equipped with a trailer hitch, you’ll find the K_CAN wires at the back, so you don’t need to take wires all the way to the front.
If you are new to the CAN bus network, keep in mind that the wires have to be twisted. The wires are twisted because the signals conveyed on the wires are based on measurements taken on both wires; as a result, when the wires are twisted together, they are both subject to the same interference, reducing the probability of a discrepancy.
To twist the wires, I always use this method:
Where to find K_CAN on F30?
The K_CAN bus network heavily depends on the vehicle equipment. To make your retrofit easier, you should first check what is the easiest way to connect to a K_CAN network.
TRSVC control unit
This is the control module for the rear-view/surround-view camera and it is located in the trunk for F1x and F2x, and in the driver footwell for the F3x models. So, for the 1, 2, and 5 Series you can go with this one. Just find the orange/green and green wire and connect to them.
AHM control unit
This is the tow hitch module, also located in the trunk. This will be the easiest one.
IHKA (Climate Control), CON (iDrive Controller), SMFA (Seat Module Driver), or SMBF (Seat Module Passenger)
These modules are not so convenient, but here we could choose the passenger seat module. On the other hand, when you are already there, just go to the FEM module for a cleaner installation.
The ground wire (Pin 4) can be connected to the ground connection point in the trunk (left).
TPMS Retrofit Coding
It can’t get simpler: just add 2VB to the VO and code FEM, ICM, HU_NBT/CIC/Champ…, KOMBI, and DSC.
If you have any more questions, write below in the comments and I’ll try to do my best.