Tire Pressure Sensor: Service and Repair
WM 443219 Removing and installing wheel electronics
Technical values
Removing and installing wheel electronics
General information
The Tyre Pressure Monitoring (TPM) system is designed to constantly monitor the tyre pressure when the vehicle is moving and 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 instrument cluster if required. In this way, the driver is warned and informed if the tyre pressure needs to be adjusted.
There are various versions of the wheel electronics -A-. In the case of the Cayenne, versions with amplified transmitting power are used. These transmit in a high frequency range of:
- 433 MHz or 315 MHz.
Information
When installing new wheel electronics units, always check that they are assigned correctly. See Technical Information -> 443200 Tyre Pressure Monitoring (TPM) system not active after changing wheels.
The following points can be used as distinguishing characteristics:
- The labelling - 433 MHz or 315 MHz
- The colour (dark grey - 433 MHz; light grey - 315 MHz).
- The part number
- No stars on the left and right of the slot
Wheel electronics unit (shown as an example)
Removing wheel electronics
Information
- For vehicles with Tyre Pressure Monitoring, 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- must 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 -A- must be replaced if:
Wheel electronics unit (shown as an example)
- The housing is visibly deformed
- The filter surface (round, porous section on back of wheel electronics) 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 bed.
Wheel electronics unit fitted (shown as an example)
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 the 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.
Every tyre set or wheel change must be communicated to the control unit. In particular, this is necessary when wheel positions have been interchanged. To do this, always select the tyre type and tyre size under main menu > Tyre pressure > Settings in the instrument cluster. The control unit then learns the wheel positions again while the vehicle is driving.
1. Clean the valve bore very carefully (visual inspection).
Information
When replacing the wheel electronics -
- Always use a completely new valve.
- Always use a new fastening screw.
2. Install the wheel electronics unit loosely at the valve (do not tighten) and position it in the valve bore together with the new valve and bead seat sealing ring.
Information
Counter the new valve with an assembly pin (supplied with the new valve).
- The valve-stem seal may become twisted and can cause damage.
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.
Countering TPM valve while tightening (shown as an example)
4. Push wheel electronics unit -A- slightly into the rim bed (this adjusts the inclination angle of the valve with respect to the wheel electronics unit).
Wheel electronics unit fitted (shown as an example)
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.
5. Tighten self-locking (Torx) fastening screw T 20 to the specified tightening torque => Tightening torque: 4 Nm (3 ftlb.)+/-0.5 Nm (+/-0.5 ftlb.). The wheel electronics unit should now be lying evenly against the rim.
Information
The wheel electronics must not come into contact with the tyre mounting paste or solvent.
When mounting tyres, ensure absolute cleanliness around the wheel electronics unit.