Tire Pressure Monitoring System, Basic Function - GF40.15-P-1000A
Model All (4xWD)
Model All (CAR)
with code 475 (Tire pressure monitor (TPM))
Example illustration of tire pressure sensors
Overview
This document contains information on:
- General
- Function requirements
- Function
- Tire pressure monitor
- Tire pressure sensors
- Leak detection (rapid pressure loss)
- Automatic fill detection
- Automatic teach-in process for tire pressure sensors of tire pressure monitoring system control unit
General
The tire pressure monitoring system monitors the tire pressure under various variables. In the event of a relevant pressure loss a warning message is issued to the driver.
The tire pressure monitoring system control unit (2) is located externally on the underbody, in the vicinity of the vehicle's driver's or front passenger seat.
Function requirements
- Ignition ON (circuit 15)
- Overspeeding from 15 to 20 km/h or a change in tire pressure > 10 kPa
- Tire pressure sensors (1) present and operational
Function
Tire pressure monitor
The tire pressure monitoring system monitors the air pressure in the individual tires by comparing the measured pressure with a previously stored reference pressure. If a relevant loss of pressure occurs, a warning message is issued to the driver, when possible with the specified location. The type of warning varies depending on the amount of pressure loss. Data such as tire temperature, outside temperature, vehicle speed and kilometer reading are also taken into account for the warning logic in the event of pressure loss.
Run-on:
When the ignition is switched off, the tire pressure monitoring system control unit (2) remains active for another 19 min and may receive signals from the tire pressure sensors (1) by radio frequency. The network interface changes to sleep mode during the run-on period.
Tire pressure sensors
The tire pressure sensors (1) are screwed onto a metal tire valve on the inner rim side of each tire.
The tire pressure sensors (1) transmit the tire pressure as well as the tire temperature. The temperature warning is only issued at high speed, generally upward of 180 km/h. A colored marking for the affected tires is shown on the instrument cluster depending on the given load in yellow or red. Tires at temperatures close to the limit value are shown in yellow. Tires that exceed the limit value are shown in red and a warning message appears. If the "Tire overheated" warning message is still shown after a period of 2 minutes, a prompt is shown to reduce the speed and a warning tone is issued. As soon as the speed drops to less than 100 km/h, this message disappears and the tire temperature display is shown.
Battery status:
With every radio message, the tire pressure sensors (1) transmit a battery status signal in 10% increments, thus providing an indication of the remaining life. For this, the tire pressure sensor (1) takes into account the energy consumption for the pressure, temperature, and motion detection, as well as the self-discharge of the battery. If the tire pressure monitoring system control unit (2) repeatedly receives a low battery status from at least one tire pressure sensor (1), a fault is logged.
Diagnosis:
To teach in tire pressure sensors (1), the teach-in process can be started using XENTRY Diagnosis COM Kit in the "Control unit adaptations" menu and "Write wheel electronics identification number" submenu.
As a result of the manually performed reduction in tire pressure, the deflation consecutively causes each tire pressure sensor (1) to send a data log. The tire pressure monitoring system control unit (2) can then save the individual serial numbers of the tire pressure sensors (1) and assign them to the correct wheel position. To enable the data to be read out, at least 30 kPa of air must be released.
Instead of lowering pressure, a trigger tool (MB3000) may be used. The trigger tool causes the tire pressure sensors (1) to transmit a data log.
A warning message is canceled if the following events occur:
- Filling to specified pressure
- Successful automatic fill detection
- Manual restart
The warning threshold of the soft warning is defined as follows:
- Pressure loss > 14% for t = 8 min
- Pressure loss > 14% for t = 18 min (USA version)
The four tire pressure sensors (1) transmit radio messages to the tire pressure monitoring system control unit (2) every 30 s while driving at a speed > 20 km/h. These radio messages contain the pressure, the tire air temperature, the individual serial number and status information. After the trip starts, the sensor positions are identified automatically within the first 10 minutes. For this, the correlation of the ABS wheel pulse counters with the signals from the tire pressure sensors (1) is evaluated.
Monitoring of tire temperature:
| Warning message | Soft warning (correct tire pressure) | Hard warning (Check tires) | Rapid pressure loss (caution tire defect) |
|---|---|---|---|
| Pressure loss | > 14% | > 20% | 20 kPa/min |
Leak detection (rapid pressure loss)
If there is progressive pressure loss when driving > 20 km/h, it is assumed that a tire is defective. In this case a warning is triggered even before the triggering criterion for the hard warning is reached. The warning occurs at the latest 120 s after the start of a pressure loss of 20 kPa/min and is displayed in the instrument cluster as the warning message "Caution Tire Defect".
When the ignition is switched back on after a leak has been detected, the display message "Check tires" appears on the instrument cluster. If, after starting a journey, the respective pressure matches the reference value again, the "Check tires" display message disappears.
Together with a tire pressure warning message, the yellow tire pressure warning lamp in instrument cluster lights up. It also lights up at the next ignition cycle until the warning message is canceled.
Automatic fill detection
Automatic fill detection is performed if - at the start of a journey - a change in pressure of more than 20 kPa was detected. For comparison, temperature-compensated and filtered pressure values are drawn on and compared against the values for the last journey. After approx. 2 min pf driving and a successful plausibility test, the new tire pressures are automatically adopted as reference values. A pressure differential between the right and left wheel of more than 17% is deemed to be implausible.
Automatic teach-in process for tire pressure sensors of tire pressure monitoring system control unit
When the ignition is switched off, the tire pressure monitoring system control unit (2) remains active for another 19 min and may receive signals from the tire pressure sensors (1) by radio frequency. After a parking period of more than 19 min, the automatic detection and localization of the tire pressure sensors (1) commences when the journey starts. A new tire pressure sensor (1) is automatically taught in after a maximum driving time of 9 min. If the tire pressure monitoring system control unit (2) has been replaced, the XENTRY Diagnosis COM Kit must be used to perform the guided "Commissioning" routine.
| Function schematics | |||
| Function schematic for tire pressure monitor | Model 118, 167, 177, 243, 247, 293 | PE40.15-P-2500-97A | |
| (TPM) | |||
| Model 213, 238, 257, 290 as of model year 2021 | PE40.15-P-2500-97B | ||
| Models 192, 206, 214, 223, 232, 236, 254, 294, | PE40.15-P-2500-97C | ||
| 295, 296, 297 | |||
| Model 464 | PE40.15-P-2500-97D | ||
| Component descriptions | |||
| Tire pressure sensor, component description | Model 223 | GF40.15-P-5130A | |
| Model 206 | GF40.15-P-5130C | ||
| Model 297 | GF40.15-P-5130D | ||
| Model 295 | GF40.15-P-5130E | ||
| Model 232 | GF40.15-P-5130F | ||
| Model 296 | GF40.15-P-5130G | ||
| Model 254 | GF40.15-P-5130H | ||
| Model 464 | GF40.15-P-5130J | ||
| Model 214 | GF40.15-P-5130K | ||
| Model 294 | GF40.15-P-5130N | ||
| Component description for tire pressure monitor control unit | Model 223 | GF40.15-P-5124A | |
| Model 243 | GF40.15-P-5124B | ||
| Model 206 | GF40.15-P-5124C | ||
| Model 297 | GF40.15-P-5124D | ||
| Model 295 | GF40.15-P-5124E | ||
| Model 232 | GF40.15-P-5124F | ||
| Model 296 | GF40.15-P-5124GG | ||
| Model 254 | GF40.15-P-5124H | ||
| Model 464 | GF40.15-P-5124J | ||
| Model 214 | GF40.15-P-5124K | ||
| Model 118, 177, 247 as of model year 2023 | GF40.15-P-5124L | ||
| Model 167 as of model year 2023 | GF40.15-P-5124M | ||
| Model 294 | GF40.15-P-5124N |