GF40.15-P-0001CW Tire Pressure Monitor Function

GF40.15-P-0001CW Tire pressure monitor function
- with CODE (470) Tire pressure monitor (base)

Function requirements
^ Circuit 15 On
^ Tire pressure monitor (TPM [RDK]) system functional

General information
The TPM [RDK] system assists the driver in checking the tire inflation pressure thus contributing to active safety.

The TPM [RDK] system monitors the air pressure in the individual tires. A previously stored tire pressure is used as a comparative value. In the event of a relevant pressure loss a warning message is issued to the driver.

The tire pressure measuring range extends from
p = 0 and 5.5 bar.

The TPM [RDK] comprises the following subfunctions:
^ Tire pressure sensing
^ Warning messages
^ Manual restart
^ Automatic fill detection

Tire pressure sensing function sequence
The tire pressure monitor control unit (N88) is permanently operational. Each time the interior CAN is activated the tire pressure monitor control unit runs a re-initialization routine.

During a journey the TPM [RDK] system continuously monitors the tire pressure of all rotating wheels
(for circuit 15 OFF for t = 20 min).

During a journey the left front tire pressure sensor (A6911), right front tire pressure sensor (A69/2), left rear tire pressure sensor (A69/3) and right rear tire pressure sensor (A69/4) transmit data telegrams every t = 60 s.

These data telegrams contain the pressure, tire pressure temperature, individual serial number and status information (manufacturer, direction of rotation, operating mode etc.). The data are transmitted by radio to the tire pressure monitor control unit. When sensing the tire pressures the tire pressure monitor control unit also takes the outside temperature and vehicle speed into consideration. The data are sent over interior CAN.

The vehicle speed is transmitted by the instrument cluster (A1). The outside temperature is recorded by the outside temperature sensor (1314) and transmitted by the front SAM control unit with fuse and relay module (N10/1).

Any malfunctions or system faults that occur are shown in the multifunction display (A1p13) in the instrument cluster.

Warning message function sequence
A warning is issued when a relevant loss of pressure has been detected in at least one of the tires. The warning is issued without any position data.

The driver receives feedback on the multifunction display in the instrument cluster or via the tire pressure monitor warning lamp (A1e66).

A differentiation is made between two types of warning messages:
^ Soft warning
^ Hard warning

Soft warning
The warning is issued immediately after a journey is ended (circuit 15 OFF).

Tires lose air over the course of time through diffusion. This is why convenient feature provides the driver with a message in good time about the need to correct tire pressures.

Warning threshold:
^ Pressure loss from p >/- 0.25 bar

If the tire pressure drops below a warning threshold for t >
10 min, a warning signal is issued, filed in the tire pressure monitor control unit memory and then displayed after circuit 15 OFF in the instrument cluster.

If, during this period, the tire pressure increases again to min. 0.1 bar under the stored comparative value, the warning message is suppressed.

Warning cancellation:
^ Warning threshold no longer dropped below
^ Successful automatic fill detection
^ Manual restart

Hard warning
While driving the hard warning informs the driver of a significant pressure loss which is relevant to safety.

Warning threshold:
^ Pressure loss of 20 % or p >/- 0.5 bar

At a pressure loss of p < 0.7 bar the warning message display is delayed for t = 5 min. If, during this period, the tire pressure increases again to min. 0.2 bar under the stored comparative value, the warning message is suppressed.

At a pressure loss p >/- 0.7 bar the tire pressure monitor warning lamp immediately comes on and the warning message is shown in the multifunction display.

If a leak is detected (air extraction p >/- 0.2 bar/min) the warning message is issued before the warning threshold is reached.

The tire pressure monitor warning lamp is not actuated however until the permissible pressure loss is exceeded or until the next ignition sequence (circuit 15 ON).

Warning cancellation:
When the ignition is switched on again (circuit 15 ON) the tire pressure monitor warning lamp is initially actuated again. The warning is canceled by a successful automatic fill detection or a manual reactivation restart.

Manual restart function sequence
The left multifunction steering wheel button group (S110) and the right multifunction steering wheel button group (S111) can be used to reactivate the tire pressure to be monitored over the tire pressure monitor menu in the instrument cluster.

The signals are read in by the steering column module control unit (N80) over the steering LIN and then transmitted over the chassis CAN to the instrument cluster. The pressure thresholds for the warnings are determined on the basis of the pressure values at the time of the restart.

Operation feedback is issued immediately over the instrument cluster.

The tire pressure monitor control unit filters the new pressure values for t = 5 min from the start of the journey and checks their plausibility.

Where new wheels are concerned or where a vehicle has been stationary for t > 19 min. the automatic wheel detection and axle assignment have to be disconnected first over the tire pressure sensor.

Automatic fill detection function sequence
Automatic fill detection is performed if a change in pressure of more than p = 0.2 bar was detected on at least two of the wheels. Temperature-compensated and filtered pressure values can be used here for comparison.

The new reference values are stored if the plausibility check is passed.