Tire Pressure Sensor: Service and Repair
WM 443219 Removing and installing wheel electronics
General information on wheel electronics
The Tyre Pressure Monitoring system is designed to constantly monitor the tyre pressure during driving and when the vehicle is stationary. One set of electronics -A- per tyre is mounted in the rim well base. These measure tyre pressure and temperature at regular intervals and transfer the values to a central control unit via a high-frequency route. The control unit evaluates the information and transfers the data to the combination instrument if required. In this way, the driver is warned and informed if the tyre pressure has to be corrected.
Wheel electronics
There are various types of wheel electronics -A- available.
The fundamental difference is in the TPM generation (1st generation up to 2008 model or 2nd generation from 2009 model onwards) and also in the frequency (433 MHz or 315 MHz).
1st generation TPM wheel electronics up to 2008 model are not compatible with 2nd generation TPM wheel electronics as of 2009 model.
If wheels with 1st generation TPM wheel electronics are fitted on a vehicle with 2nd generation TPM wheel electronics (or vice versa), the TPM system will not recognise the wheel electronics. The TPM system is not active and a corresponding warning message appears in the instrument cluster.
In addition, the wheel electronics are reported as defective in the fault memory of the TPM control unit.
Refer to the Technical Information for more information and an overview. -> 443200 Tyre Pressure Monitoring (TPM) system not active after changing wheels (17/08).
The following points can be used as distinguishing characteristics of wheel electronics:
- Labelling - 433 MHz or 315 MHz
- Refer to the Parts Catalogue (PET) for details of part numbers/current allocation
- Colour
- Without 8 stars (the illustration shows 8 stars, 4 each to the left and right of the slot, wheel electronics with amplified transmission power from the Cayenne)
- Special wheel electronics - 315 MHz: Indicated by 14 slashes
Wheel electronics components
Removing and installing wheel electronics
Removing wheel electronics
Information
- For vehicles with a tyre pressure monitoring system, the valve and wheel electronics are only replaced in exceptional cases! The following points can make replacement necessary!
Valve complete with screw -1 to 7- has to be replaced if:
- The wheel electronics unit is removed
- The self-locking -1- fastening screw is loose
- The bead seat sealing ring -6- is porous or damaged
- The valve body -7- is bent
- The union nut -4- is loose.
The wheel electronics unit -A- must be replaced if:
- The housing is visibly deformed
- The filter surface (rectangular or round, porous section on back of wheel electronics unit) is so badly soiled that it can no longer be cleaned by wiping
- Tyre sealant (tyre sealing liquid) has been used
- The service life of the battery has expired
- There is a fault within the wheel electronics unit.
After removal of the tyre, the wheel electronics unit -A- can be seen at the valve in the outer rim well base.
1. Release the wheel electronics unit from the valve using a Torx socket screwdriver T 20 (counter with a suitable assembly pin if necessary, e.g. steel pin with diameter of approx. 1.8 mm in bore at valve foot) and remove it. The new valve comes with an assembly pin. This can also be used for removing the wheel electronics unit.
Countering TPM valve while loosening
2. Then unscrew union nut and remove valve.
Installing wheel electronics
Information
Carry out the tightening procedure to the specified torque for the valve in the rim once only. Remove the assembly pin after fitting the valve. The tyre can be damaged if the assembly pin is left in the valve.
When replacing the wheel electronics unit, always use a completely new valve and a new fastening screw!
The tightening torque for wheel electronics unit/valve is 4 Nm/3 ftlb. (+/- 0.5 Nm/0.5 ftlb.)!
Every tyre set or wheel change must be communicated to the control unit. In particular, this includes the case where wheel positions have been interchanged. For this purpose, always select the tyre type and tyre size under Main menu > Tyre pressure > Adjustments in the instrument cluster. The control unit then learns the wheel positions again once the vehicle starts driving.
1. Clean the valve bore very carefully (visual inspection).
2. Install the wheel electronics unit loosely at the valve (do not tighten) and position in valve bore together with valve and bead seat sealing ring.
3. Fit the washer, chamfered on both sides, from outside and screw on the union nut until it is seated correctly. Visibly screw in the bore at the valve foot and block it using the supplied assembly pin. The tightening torque is 4 Nm (+/- 0.5 Nm)/3 ftlb. (+/- 0.5 ftlb.)
Countering using assembly pin in bore at the valve foot when tightening TPM valve
Information
When tightening the wheel electronics unit/valve, tighten to the specified tightening torque evenly and in one movement. The tightening process must not be interrupted.
- Remove the assembly pin after tightening the components.
- The tyre can be damaged if the assembly pin is left in the valve.
4. Push wheel electronics unit -A- slightly into rim well (this adjusts the angle of inclination of valve to wheel electronics).
Carefully tighten self-locking (Torx) fastening screw T 20 to 4 Nm/3 ftlb. +/- (0.5 Nm/0.5 ftlb.). Block with the supplied assembly pin while doing this. The wheel electronics unit should now be lying evenly against the rim.
Information
When coating the rim with tyre mounting paste, make sure not to coat the area around the wheel electronics. Tyre mounting paste must not get under the wheel electronics or into the filter area. This can damage the wheel electronics.
Countering using assembly pin in bore at the valve foot when tightening wheel electronics unit