Tire Pressure Monitoring System (TPMS), System Overview (GROUP 44, NO. 09-01)

Tire Pressure Monitoring Sensors

• Mounted to valve stem of each individual wheel.
• Activated by centrifugal motion (wheel rotation) or by rapid pressure change.
• Wheel rotation of 25 km/h (16 mph) or above will start signal that includes tire pressure, tire temperature, tire acceleration and identification number.
• Even without tire rotation, a pressure increase or decrease will cause the sensor to send a signal.
• 315 MHz transmission frequency.

Antenna

• Central Locking and Anti-Theft Alarm System Antenna -R47- receives signals from tire pressure sensors.
• -R47-, located on the A-pillar, provides input to Comfort and Convenience Control Module -J393-, which is located behind the glove box.

Tire Pressure Monitoring Control Module -J502-

• Is integrated in the Comfort and Convenience Control Module -J393-.
• Does not identify where sensors are, only collects information from sensors.
• Controls tire pressure warning lamp on instrument cluster.

Tip:  There is no warning for pressure above the nominal.

Tire Pressure Warning Lamp -K230-

• Will illuminate in combination with warning message in the MFI when pressure is low.
• When tire pressure is 0.5 bar (7 psi) below nominal (0.4 bar/6 psi for SW 391), Message in cluster reads "Tire Pressure Too Low".
• Rapid loss of pressure of more than 0.2 bar (3 psi) per minute. Message in cluster reads "Low Tire".

Tire Filling

• Check tire pressure using an accurate and reliable pressure gage.
• Tires must be filled when cold.
• Pressure displayed on the scan tool is delayed for up to 2 minutes while filling is completed.

Adaptation

After replacing a sensor, the TPMS system must be re-learned by performing the following:

Vehicle must be parked for a minimum of 20 minutes (with ignition switched ON for SW 391, and Midtronics InCharge 940 (INC 940) battery charger/maintainer connected), before the TPMS system will go into a learn mode.

• Start and operate vehicle over 25 KM/h (16 mph) for at least 7 minutes.
• TPMS then recognizes sensor inputs.
• Warning light in cluster will go out.

Guided Fault Finding Test Plans Available

• Measuring Value Blocks.
• Coding the Tire Pressure Monitoring Control Module -J502-.
• Checking adaptation values for specified pressures.
• Radio interference.
• CAN Bus malfunction.

Determining Sensor Location

Using VAS 5051/5052 diagnostic tool in Self Diagnosis, AW 65, MVB 16:

• Lower the pressure in one tire by 0.7 bar (10 psi).

The rapid pressure loss will trigger this sensor to send a signal which appears in MVB 16 within 2 minutes.

• Record the sensor ID and wheel location. Repeat for other wheels.
• If one wheel does not respond the sensor may not be recognized by the antenna. Move vehicle by 1/2 a tire revolution (180 degrees) and retest.
• No signal from one wheel (after re-test) indicates a faulty sensor.

Tip:  All values in MVB 1 thru 12 are erased every time the ignition is switched OFF after driving. 'Not recognized' will be displayed in those MVB's until a new signal is received during regular operation.

Temperature Compensation

Fig 1: Temperature Compensation Graph

• The system measures the ambient temperature once a day and creates a median reference temperature (T_Ref ) from the last two weeks. This reference is the basis for the above diagram.
• As temperature goes up (to the right of T_Ref ), the nominal tire pressure has to be set accordingly. Example: Cold tire nominal of 2.5 bar has to be set to 2.7 bar, if the tire temperature is 20°C above T_Ref .
• The same applies to the warning light reset line. The light normally goes out, when the pressure gets within 0.15 bar (2.2PSI) of the nominal, here 2.35 bar. At 20°C above T_Ref however, it will take 2.6 bar, for the light to go out.
• It is always a good idea to overfill the tire generously (not to exceed max. tire pressure rating printed on tire) to ensure, that neither an incorrect gage, a warm tire, or a combination of both, prevent the light from going out.
• If the ambient temperature outside the workshop where the vehicle is operated is lower, add pressure to the nominal (see tire pressure label) to compensate. Add approximately 0.1bar per 10°C (1.5 PSI for every 20°F) difference. This also applies to warm tire vs. cold tire conditions.

Troubleshooting

• Does the TPMS light blink (SW 420 and later) for 65 seconds when the car is started, before staying on solid?
  1. NO  - low pressure issue
  2. YES  - TPM system issue

Light NOT blinking:

For highline cluster only - accompanied by Warning message:

• "Tire pressure low" - appears after a slow pressure loss in one or more tires
• "Low Tire" - appears after a rapid pressure loss.
• Solution - adjust pressure and/or repair/replace damaged tire

Tip:  Exception: Some (A5) Jetta's with ABS/ESP 4 digit coding such as 4738; if the warning light does not go out after a low pressure condition has been found and corrected, recode ABS/ESP using GFF.

Light is blinking:

• Use GFF or check for DTC's (see flow chart attachment)