184000347 - T.P.M.S. SYSTEM
General specifications
The TPMS Tyre Pressure Monitoring System checks the pressure of the tyres sending the necessary information to the Body Computer via the A-Bus network.In particular, if the inflation pressure is below what it should be, the system activates an insufficient pressure signal in the instrument panel or warns that one or more of the tyres is punctured.The system consists of a receiving control unit located inside the passenger compartment (luggage compartment crossmember, right hand side) and four transmission sensors located inside the tyre on the rim. | This function is only available on trim levels with Comfort instrument panels. |
Transmission of tyre status via a-bus/b-can
The tyre pressure control unit (CPP) acquires information, via radiofrequency, from the sensors, relating to the state of all four tyres and transmits it to the Body Computer via the A-BUS serial line.The Body Computer transmits the following signals via the B-CAN:
- CPP control unit programming/characterization status;
- possible entire system fault;
- tyre position;
- tyre inflation pressure status;
- tyre temperature status.
Tpms operating principle
At the key-on the control unit sends the Body Computer a confirmation signal indicating that it is working properly via the BUS serial line.When the vehicle moves at a speed of at least around 16 km/h, the sensors measure the pressure and transmit the tyre pressure and temperature status via radiofrequency; the receiver receives this transmission from the sensors located inside the tyres, immediately forwarding this information via the BUS serial line.When the value of the pressure goes below the pre-set level, the control unit signals the alarm status to the Body Computer, via the A-Bus, which, on conversing with the Instrument Panel via the B-Can, switches on the visual and acoustic warning messages.From the key-on onwards the TPMS sends a message very 15 seconds via the Bus serial line which is designed to signal to the Body Computer that it is present and working properly. If the Body Computer does not receive any of these messages for a minute it notifies the Instrument Panel that the TPMS is faulty.Intervention levels
There are two intervention levels which are stored in the receiver memory.The first (known as the CHECK level) is designed to signal if the pressure of one or more of the tyres is slightly below the optimum level in which case the driver should check it and restore the correct value: CHECK = drop in pressure of 0.3 bar in relation to the nominal value.The second level (known as the WARNING level), on the other hand, is established to signal a loss in pressure due to the fact that one or more of the tyres is presumed to have a puncture: WARNING = drop in pressure of 0.6 bar in relation to the nominal value.The third level (known as the General level) is established to signal a presumed puncture if the pressure of the tyre is below 1.5 bar: General = pressure below 1.5 bar (limit level irrespective of the optimum pressure value memorized).Display in instrument panel
The instrument panel acquires these signals and manages the readings as described below.When the pressure value of one or more tyres exceeds the CHECK level (nominal pressure - 0.3 bar) the warning light comes on in the instrument panel and an alphanumerical message appears on the display e.g. "front tyre minimum pressure > " accompanied by an acoustic warning. When the signalling cycle is over only the warning light remains activated in the panel until the correct pressure is restored.The warning cycle is repeated after 10 minutes (once).If the panel receives a signal that the pressure is below the WARNING level (nominal pressure - 0.6 bar), the "tyre punctured" warning light and the message in the alphanumerical display are activated, accompanied by an acoustic signal dependent on the "priority 0" fault logic. Characteristic of working principle 5560 INSTRUMENTSWhen the signalling cycle is over only the warning light remains activated in the panel until the correct pressure is restored.If there is a fault in the tyre pressure control unit, the "general failure" warning light and the corresponding alphanumberical display in the "tyre monitoring system" display are activated.This takes place in the following cases:
- fault in the control unit wiring and circuit;
- no signal received from one or more sensors (sensor battery run down, faulty, broken)
- TPMS control unit faulty
- use of one or more wheels without sensors (e.g. with snow tyres)
The display occurs when the CAN message is received if and only if the vehicle speed is above 20 km/h for longer than 30 seconds. | If the Body Computer, correctly set, does not receive a message for longer than a minute, it sends the CPP fault signal which is displayed by the NQS. |
System not programmed: if the tyre pressure control unit has not been programmed, the following alphanumberic message is shown on the display "System Not Programmed"Tyre pressure control unit (cpp)
The CPP is connected to the rear wiring by means of a bridge.The receiver electronics are housed in a plastic casing not screened for RF purposes; it is also treated with resin to prevent climatic conditions from affecting its correct operation.The fastenings allow the control unit to be fitted securely in position (preventing rotation).The CPP is an electronic component which, connected to the A-BUS serial line, manages the function of checking the tyre pressure and carries out a fault diagnosis via the K line.The receiver control unit also possesses a diagnostic function in order to evaluate the effective operation of each sensor and of the entire system. It detects:
- faults in the control unit wiring and circuit;
- no signal received from one or more sensors;
- faults in the actual control unit;
The pressure management software includes a pressure measurement compensation strategy which varies according to the temperature. | If there is a break in the control unit power supply, the new sensor ID codes should not be stored in the control unit memory; the IDs and the position of the sensors, as well as the error codes (fault diagnosis) remain stored in the control unit EEPROM. |
Control unit pin out
The control unit is illustrated below.| PIN | FUNCTION |
|---|
| 1 | EARTH |
| 2 | N.C. |
| 3 | N.C. |
| 4 | N.C. |
| 5 | N.C. |
| 6 | N.C. |
| 7 | CONTROL UNIT DIRECT POWER SUPPLY |
| 8 | N.C. |
| 9 | CONTROL UNIT IGNITION-OPERATED POWER SUPPLY |
| 10 | DIAGNOSTIC LINE K |
| 11 | A-BUS SERIAL LINE |
| 12 | N.C. |
Control unit replacement
If the CCP is being replaced, the sensor ID codes must be programmed as described below.If this is not the case, the system will no longer be capable of working and the instrument panel will show the "system not programmed" warning described previously.TYRE INFLATION PRESSURE SENSORS
The sensors are located inside the wheel rims in place of the normal tyre inflation valve.The sensors have the function of checking the value of the pressure and tempearture of each of the tyres and transmitting the information via a radiofrequency signal (433.92 MHz) to the control unit/receiver.The sensors measure the pressure and the temperature inside the tyre by means of dedicated pressure and temperature sensors which are combined with electronics for acquiring and processing the signals and are equipped with a section designed for transmitting these signals at a radiofrequency of 433.92 MHz.The sensor assembly is supplied by a 3.6 V lithium battery that lasts 10 years in normal usage conditions.When the battery is run down, a specific sensor battery run down message is sent to the instrument panel and the sensor should be replaced with a new one and its ID programmed in the control unit as described below. | All the parts of the sensor and the valve are compatible with the fluid supplied by Fiat Auto for rapid tyre repairs. The opening in the sensor for air allows the sealant fluid to be introduced into the tyre without a problem. |
Composition
1 - Nut2 - Valve cover3 - Valve4 - Sensor5 - Valve opening6 - Resin treated surface7 - Tapered sealProgramming the sensor ids in the control unit
In the case of:
- replacing the CPP;
- replacing a sensor;
- changing the position of a wheel (e.g. swapping front - rear) the procedure described must be carried out in order to memorize the sensor ID code in the control unit so that the control unit can recognize them as belonging to the system and consequently managing the RF signals coming from them.
In order to carry out this check the special equipment illustrated in the diagram is needed which "wakes up" the actual sensor with a 125 kHz transponder: for a minimum application time of 5 seconds. This equipment certifies the RF operation of the sensor.Using the learning routine through the diagnostic equipment the identification code is written in the control unit memory. In this way the control unit recognizes transmissions coming from the new sensor and manages them correctly.If the new sensor ID is not programmed in the control unit, the instrument panel will display a "tpms failure" message (1 sensor missing) after the vehicle has travelled for 12 minutes at a speed of at least 16 km/h.