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

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

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

The status of circuit 15 is transmitted by the electronic ignition lock control unit (N73) over the interior CAN (CAN B).

TPM [RDK), 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 specified air 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 to 6.375 bar.

The TPM [RDK] comprises the following component functions:
^ Tire pressure sensing function sequence
^ Warning message function sequence
^ Manual restart function sequence
^ Automatic fill detection function sequence
^ Learn mode function sequence

Tire pressure sensing function sequence
During a journey the TPM [RDK] system continuously monitors the tire pressure of all rotating wheels (with circuit 15 OFF run-on time of t = 19 min).

During a journey the left front tire pressure sensor (A69/1), 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 sent by the control unit tire pressure monitoring (N88) per radio frequency.

Axle localization is performed by evaluating the reception level of the tire pressure sensors. Side localization is based on the right/left information of the tire pressure sensors.

In addition, the tire pressure monitoring control unit incorporates the outside temperature and the vehicle speed into the warning logic.
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 (B14) and transmitted by the front SAM control unit with fuse and relay module (N10/1).

Any warning messages and menu displays are shown on 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).

The warning messages are made up of the following component functions:
^ Soft warning function sequence
^ Hard warning function sequence
^ Leak detection function sequence (rapid pressure loss)

Soft warning function sequence
A soft warning message 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 of p >/- 0.25 bar

If the tire pressure of at least one tire is continuously below the warning threshold for t = 12 min during a trip, a warning signal is set, stored in the memory of the tire pressure monitoring control unit and displayed in the instrument cluster at the end of the trip (circuit 15 OFF).

If the tire pressure increases again to at least p = 0.1 bar under the stored specified value, the warning message is suppressed. Warning cancellation:
- Value is no longer below warning threshold
- Successful automatic fill detection
- Manual restart

Hard warning function sequence
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

In the event of a pressure drop below the warning threshold, a warning message is displayed in the multifunction display after t = 5 min at the latest and the tire pressure monitor warning lamp is actuated. If the pressure loss is very high (p 0.2 bar below the warning threshold), the warning message is issued after t = 1 minute at the latest.

If a leak is detected (air extraction p >/- 0.2 bar/min) the driver is notified with a warning message "Warning! Tire defect".

The tire pressure monitor warning lamp is actuated together with a hard warning message, which is repeated during the next ignition sequence.

Cancelation of warning message:
- Successful automatic fill detection
- Manual restart

Leak detection function sequence (rapid pressure loss)
If progressive pressure loss is detected during a certain period (gradient) of time while driving, it is assumed that a tire is defective. In this case a warning message is triggered, even before the triggering criterion for the hard warning message is reached. The warning message is generally issued at the latest t = 120 s after the start of a pressure loss of p = 0.2 bar/min and is shown as a warning message (red) "Warning! Tire defect" on the upper multifunction display in the instrument cluster.

Cancelation of warning message:
During an ignition sequence, the warning message can be canceled by successful filling detection or by a manual restart. When the engine is switched back on after a leak warning message, the tire pressure monitor warning lamp in the instrument cluster is initially activated. If after the start of a journey new pressure values exist and no warning criterion is met, the tire pressure monitoring warning lamp is switched off and the warning message is cleared.

Manual restart function sequence
When the TPM [RDK] system is restarted, the tire pressures set by the driver are adopted by the tire pressure monitoring control unit as the new specified values.

The left multifunction steering wheel button group (S110) and the right multifunction steering wheel button group (S111) can be used to call up and scroll through the TPM [RDK] menu in the instrument cluster. With the ON button (S110s6) you can enter the submenu for restarting the TPM [RDK] system
The signals are read in by the steering column tube module control unit (N80) via steering LIN (LIN E1) and transmitted via the chassis CAN to the IC. The pressure thresholds for the warning messages 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. The smallest pressure value on each axle is then stored as the new specified value for pressure monitoring.

Automatic fill detection function sequence
Automatic fill detection takes place, if at the start of a journey a pressure change of more than p = 0.2 bar has been detected at a least 2 wheels. For comparison, temperature-compensated and filtered pressure values are drawn on and compared against the values for the last journey.

After approx. t = 5 min journey and a successful plausibility check, the new tire pressures are automatically adopted as specified values.

Learn mode function sequence
Where new wheels are concerned or where a vehicle has been stationary for t > 20 min. the automatic wheel detection and axle assignment have to be disconnected first over the tire pressure sensor.

A new tire pressure sensor undergoes teach-in in with a new identification number and is monitored after approx. t = 10 min. Side localization is based on the right/left information of the tire pressure sensors.

Learn mode in workshops and/or correction by entry of identification number with Diagnosis Assistance System (DAS).

When working with DAS, follow the "Initial startup" routine. There are 2 variants: "Initial startup with unknown wheel IDs" and "Initial startup with known wheel IDs".