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

GF40.15-P-0001CEA Tire pressure monitor function
- with CODE (475) Tire pressure monitor (premium)

Function requirements, general
^ "Circuit 15 ON" status
^ 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).

Tire pressure monitor, general
The TPM system supports the driver by monitoring the tire inflation pressure as of vehicle speed > 10 to 20 km/h (no stationary monitoring), thereby improving active safety.

The tire pressure monitor system monitors air pressure and temperature in the individual tires. A previously stored specified pressure (specified values) for each tire is used as the reference value.
If a relevant loss of pressure occurs, a warning message is issued to the driver, when possible with the affected location. The measuring range of the Tire Pressure covers between 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
^ Function sequence for teach-in process in workshops or follow-up operations by inputting the identification number using the DAS (DAS)

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

The pressure, tire air temperature, individual serial number and status information (manufacturer, direction of rotation, operating mode etc.) are contained in these data telegrams. The data are transferred to the tire pressure monitor control unit via the radio frequency (N88).

Axle localization is performed by evaluating the reception level of the tire pressure sensors. The sides are localized by evaluating the direction of rotation information.

In addition, the tire pressure monitoring control unit incorporates the outside temperature and the vehicle speed into the warning logic. These data are provided via chassis CAN (CAN E).

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).

Warning and information messages are shown on the multifunction display (A1p13) in the IC.

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 with position detail.

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

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

Soft warning function sequence
A soft warning is issued immediately after a journey is ended (status "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.

The warning threshold is defined as follows:
- Pressure loss of p >/- 0.25 bar If, during the journey, the tire pressure of at least one wheel is below the warning threshold uninterrupted for a period of t = 12 min, a warning signal is set, stored in the memory of the tire pressure monitor control unit and at the end of the journey (status "circuit 15 OFF") displayed in the IC.

If the tire pressure rises again to at least p = 0.1 bar below the stored specified pressure, the warning message is suppressed. The warning message is canceled if one of the following events occurs:
- 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

If the tire pressure drops below the value determined by the warning threshold, after a least t = 5 min a warning message is shown on the multifunction display 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 release p >/- 0.2 bar/min) the message "Warning! Tire defective" is displayed to the driver. The tire pressure monitor warning lamp is actuated together with a hard warning, which is repeated during the next ignition sequence.

The warning message is canceled if one of the following events occurs:
- Value is no longer below warning threshold
- 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 is triggered, even before the triggering criterion for the hard warning is reached. As a rule the warning takes place 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 "Caution: tire defect" on the multifunction display in the instrument cluster.

A warning message is canceled for one of the following events:
- Value is no longer below warning threshold
- Successful automatic fill detection
- 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 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. 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.

Function sequence of learning process in workshops or correction by entering identification number with DAS
In the case of new wheels or a longer parking time of t > 20 min automatic own wheel recognition/localizing is started at the start of journey via the tire pressure sensors.

A new tire pressure sensor is taught-in automatically after driving for 10 minutes. Side localizing based on right/left information from the tire pressure sensors.

In the case of axle assignment the rear wheels which are closer to the receiver receive stronger signals than the front wheels which are further away.

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".

When working with the electrical test or CANDI new tire pressure sensors can be can be taught-in with the routine "Check for WU Remeasure Transponder. With this routine, it is possible to choose between teach-in with Trigger tool MB2000E or teach-in via pressure change. This routine is started via diagnosis and is identical for all wheel positions.

For teach-in with Trigger tool, the respective tire pressure sensor must be triggered.

The tire pressure sensor thereupon transmits a data telegram from which the wheel identifier is read out.

For teach-in via pressure change, the pressure at the corresponding wheel must be changed by 0.3 bar. The tire pressure sensor then transmits data telegrams with the changed pressure value (delta_p Frames) to the TPM [RDK] control unit. The wheel identifier is read out from these data telegrams.

The result is queried with the service "Check for WU Remeasure Transponder: Request results WU ID". The detected wheel identifiers must then be written to the respective position by the user in the diagnosis service download "Transmitter-ID's" (Left Front, Right Front, Right Rear and Left Rear).
"OK' must also be written to the service download "Axle/Side Location Status".

The tire pressure monitor control unit checks the plausibility of the wheel identifier and only authorizes one wheel identifier with the same number.