NOTE: Each road wheel is fitted with a Tyre pressure sensor (attached to the valve stem). The Tyre covers the pressure sensor and it is not visible unless the Tyre is removed. Take care when changing the Tyre to avoid damaging the Tyre pressure sensor.
The TPMS uses 4 battery powered Tyre pressure sensors to monitor Tyre pressure.
Tyre pressure sensors transmit Tyre pressure information to the BCM which compares the Tyre pressures, and identifies when a Tyre or Tyres are under inflated. When the BCM identifies an under inflated Tyre or system fault, it sends a message to the IPC to illuminate the low Tyre warning lamp and display a message in the IPC.
The Tyre pressure sensors are trained (calibrated) to the BCM, which records the unique identifier for each Tyre pressure sensor and their position on the vehicle.
NOTE: When the BCM or a Tyre pressure sensor is replaced the TPMS Tyre pressure sensor training procedure must be performed.
It is not necessary to train the Tyre pressure sensors after a Tyre rotation on vehicles with the same front and rear Tyre pressures, however the BCM cannot recognise if the Tyre pressure sensor identifiers have been moved to different positions and retains the original position information for each Tyre pressure sensor.
NOTE: When directed to train any Tyre pressure sensors,only use the sensor training procedure outlined in the workshop manual. Do not use the TPMS reset procedure outlined in the Owner's Literature as this procedure does not program new Tyre pressure sensors to the module.
System Operation
The TPMS checks the pressure of 4 road wheels and alerts the driver in the case of a significant pressure loss via a message to the IPC. TPMS offers improved functionality as it works with 4 separate sensors (one
in each wheel) that monitor Tyre pressure, Tyre air temperature and acceleration.
This allows the system not only to detect deflation in 2 or 3 Tyres, but also a consistent loss of pressure in all 4 Tyres. TPMS reacts to pressure losses of at least 20% compared to the learned warm Tyre pressure.
The 4 sensors wirelessly transmit their data to the BCM regularly, or if a pressure loss is detected, immediately. If a pressure loss is detected the BCM sends a request to the IPC to switch on the warning lamp and show a message in the IPC display.
The scan tool is a useful tool to verify the accuracy of the Tyre pressure data transmitted by the TPMS sensors. This is accomplished by comparing the BCM Tyre pressure PID (parameter identification) data to the actual Tyre pressure using a digital Tyre pressure gauge.
The scan tool is also useful in diagnosing TPMS concerns and finally may be used in conjunction with the special tool 204-324 in training the sensors to a new location after a Tyre rotation. The BCM cannot recognise that the sensor identifiers have been moved to different positions on the vehicle and would otherwise retain the original position information for each sensor.
TPMS Automatic Learning Process
After each ignition cycle the system works on factory preset parameters for 15 minutes of driving while the TPMS goes through a self learning process. In this time the system gets to know all parameters that are necessary to work precisely. The warm Tyre pressure which depends on surface temp
TPMS Wheel Sensor Training
When the BCM or a Tyre pressure sensor is replaced the TPMS Tyre pressure sensor training procedure must be performed.
The sensor training can be achieved by following the Tyre pressure sensor training procedure described in the workshop manual.
The TPMS can be put into a learning mode using the scan tool or manually using the vehicle controls (specific sequence). The Tyre pressure monitor activation tool will then be required train each sensor to it's new position on the vehicle.
TPMS Wheel Rotation and Sensor Training Faults
If a Tyre pressure sensor does not train to a BCM we need to investigate 3 possibilities.
- Tyre pressure sensors
- BCM
- Wireless interference between the sensor and the BCM
This technique can be used to differentiate between a sensor and a module concern. If the BCM in the suspect vehicle cannot train any of the sensors on the known good sensors from another vehicle, then the concern is with the module or RFI.
If a sensor in a certain location has caused several events, yet the sensor trains and seems to operate normally, moving that particular wheel to a different location on the vehicle is a good way to isolate the concern to a certain sensor/wheel location. Rotate the wheels and road test the vehicle. This can be done in an attempt to replicate the concern and help determine if the concern followed the sensor or remained in the original sensor location.
NOTE: If the vehicle has been stationary for more than
15 minutes, the sensors go into a "sleep mode" to conserve battery power and they will need to be "woken up" by driving faster than 32.2Km/h so they transmit the latest Tyre pressure information to the BCM.
NOTE: If the first sensor fails the TPMS training procedure, the BCM aborts the entire procedure. Starting the training procedure at a different wheel is a technique that can be used to determine if the remaining sensors can train to the module. This can help save time determining if one sensor is damaged, other sensors are having concerns or the BCM is experiencing training difficulties with a certain TPMS sensor location.
TPMS Warning Indicator
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- tpmserror.png (3.51 KiB) Viewed 586 times
TPMS Warning Indicator Illuminates Continuously
The TPMS warning indicator remains on continuously and the message centre displays LOW Tyre PRESSURE when any of the Tyre pressures fall below
the low pressure limit. When this condition exists, adjust the Tyre pressure to the recommended cold Tyre pressure indicated on the VC (vehicle certification) label.
TPMS Warning Indicator Flashes
The TPMS warning indicator flashes for 70 seconds and then remains on continuously when the ignition is set to ON and the TPMS is malfunctioning. The PID TP_STAT can be used to determine why the TPMS warning indicator is flashing.
- Tyre Pressure Sensor Fault - The message centre displays Tyre PRESSURE SENSOR FAULT when a Tyre pressure sensor is malfunctioning
- No communication with the BCM - The TPMS warning indicator illuminates when the IPC has not received any signals from the BCM for more than 5
seconds. The message centre displays Tyre PRESSURE MONITOR FAULT
The BCM monitors the TPMS status. The current status can be viewed by accessing the TPMS status PID: TPMS_STAT using the scan tool. This helps identify the current system status and may aid in diagnosing the system. The PID has 4 valid states:
- TPMS_STAT = SENSOR FAULT: If the BCM has not received the Tyre pressure data from 1 to 3 TPMS sensors for 10 minutes when vehicle speed is above 32.2 km/h, the PID displays SENSOR FAULT
- TPMS_STAT = SYSTEM FAULT: If the BCM has not received the Tyre pressure data from all 4 TPMS sensors for 10 minutes when vehicle speed is above 32.2 km/h, the PID displays SYSTEM FAULT
- TPMS_STAT = LOW: If the BCM has detected that at least 1 TPMS sensor is reporting low Tyre pressure, the PID displays LOW
- TPMS_STAT = ACTIVE: If the TPMS is functioning normally, the PID displays ACTIVE
The TPMS uses the TPMS last warning event PIDs to store detailed information about the last 5 times the TPMS warning indicator was activated. These PIDs can be used to acquire more information about a particular TPMS event, but must be used carefully.
Radio Frequency Interference (RFI)
RFI can be caused by:
- Video equipment has been found to cause RFI especially when the video and power supply lines are near the TPMS
- Car alarms (even those installed by the dealership) have been found to create enough RFI to cause the TPMS to malfunction or lose considerable range. These car alarms can be difficult to locate, as they are usually hidden somewhere out of the way for reduced accessibility
- Many in-vehicle cell phone chargers have been found to cause considerable RFI. The vehicles with the power access point closest to the BCM are the most affected. It must be noted that most cell phone chargers do not produce high levels of RFI all the time. This depends on the state of charge of the cell phone battery. The phone battery must be almost completely discharged in some cases
- Power supplies and DC (direct current)/AC (alternating current) inverters typically create a lot of RFI. Most consumer grade equipment has very
little filtering or shielding
In some cases the RFI may actually be caused by a module or ground on the vehicle. Depending on the severity of the concern, a dirty ground, improperly built ground shield or module can disable the system. Modules that have micro controllers using clock circuits to create timing pulses for the microprocessor may radiate RFI.
Using Customer Electronics to Pinpoint RFI
This method can be a way to determine the cause of a concern well before the sensors and module are replaced with little or no effect on system performance. Since this takes more up front work, it relies on working with the customer to determine what equipment was being used at the time of the event. Question the customer about what kind of devices they are using. Determine which power points are being used and if necessary ask
that the devices be activated to determine their affect on the TPMS.
Options for Eliminating Intermittent TPMS Operation Caused by RFI
- If an Original Equipment Manufacturer (OEM) component or customer device is causing an RFI concern, replace the device
- If a phone charger is causing an RFI concern, the customer should consult with their cell phone provider to acquire a different battery charger
- If a device such as a dealer installed alarm is causing a RFI concern, move the device to another location in the vehicle. In the case of a portable device move the power cord to another power point location
Ambient Temperature Change and Tyre Pressure
Tyre pressures fluctuate with temperature changes. For this reason, Tyre pressures must be set to specification when Tyres are at outdoor ambient temperatures. If the vehicle is allowed to warm up to shop temperatures, and the outside temperature is less than shop temperature, the Tyre inflation pressure must be adjusted accordingly.
If the Tyres are inflated to specification at shop temperatures, and the vehicle is moved outdoors when the outdoor ambient temperature is significantly lower, the Tyre pressure may drop enough to be detected by the TPMS and activate the TPMS warning indicator.
As the ambient temperature decreases by -12.2° C, Tyre pressure decreases 6.9 kPa. Adjust the Tyre pressure by
6.9 kPa for each -12.2° C of ambient temperature drop as necessary to keep the Tyre at the specified VC label pressure. To adjust the Tyre pressure indoors for colder outside temperatures, refer to the following table.
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- tp01.png (83.79 KiB) Viewed 586 times
Body Control Module (BCM)
The BCM is a multi-function module that monitors all Tyre pressure sensor inputs and all CAN messages that relate to the TPMS. The BCM records and retains the unique identifier of each of the Tyre pressure sensors.
The BCM retains the previous Tyre pressure sensor location information following a Tyre rotation, for the BCM to learn the new Tyre pressure sensor location, the Tyre pressure sensors must be trained to the BCM. Additionally, the Tyre pressure sensors must be trained when a new BCM is installed.
Tyre Pressure Sensor
Each of the 4 Tyre pressure sensors contain a battery, a Tyre pressure and air temperature sensors and a radio transmitter. The Tyre pressure sensors send wireless radio transmissions approximately once every 60 seconds when the vehicle speed exceeds 32.2 km/h.
