P Bus & I Bus
A bus is understood to be the leads over which information is sent digitally and serially. Digital means that the voltage difference between the leads has only two values, roughly 0 V and 5 V. The information is coded so that different combinations of 0 V and 5 V pulses have different meanings.
Serial means that the information is sent in "packets" which are transmitted one after the other in rapid succession.
The bus is divided into the P-bus (Powertrain Bus) and the I-bus (Instrument Bus). Both buses are connected to the main instrument unit (MIU). The buses are electrically isolated from each other.
The control module for the airbag and SRS are not connected to the bus. The TC/ABS control module on cars with Traction Control is connected to the P-bus.
The diagnostic tool is not directly connected to the bus but communicates via DICE, which is connected to the I-bus, and therefore has access to all the control modules connected to the bus.
The P-bus has a data transfer rate ten times higher than that of the I-bus. This is because the P-bus requires information with the least possible delay.
All the information sent from one control module is accessible to all the other control modules on the bus. The MIU is responsible for making information on one bus available on the other bus.
The control modules send out information on the bus at regular intervals. The time between two transmissions depends on the information being transmitted and varies between 10 milliseconds (0.010 seconds) and one second. Information is also transmitted by the control module whenever the information changes.
The transfer of information between control modules takes place on two leads, bus+ (green lead) and bus- (white lead). The leads are twisted to increase their resistance to electrical interference.
The MIU uses the following information:
| Information | Values | From | The value depends on the following sensor input, signal or function |
|---|---|---|---|
| Left Direction Indicator | ON OFF |
DICE | Control module activation of output to lamps The MIU lights the indicator lamp for LH direction indicators. |
| Right Direction Indicator | ON OFF |
DICE | Control module activation of output to lamps The MIU lights the indicator lamp for RH direction indicators. |
| Rear Fog Light | ON OFF |
DICE | Control module activation of output to fog light The MIU lights the indicator lamp for the rear fog light. |
| Door Driver | OPEN CLOSED |
TWICE | Door switch The MIU lights the driver's door symbol. |
| Door Passenger (Bus from TWICE) | OPEN CLOSED |
TWICE | Door switch The MIU lights the passenger's door symbol. |
| LH rear door | OPEN CLOSED |
TWICE | Door switch The MIU lights the LH rear door symbol |
| RH rear door | OPEN CLOSED |
TWICE | Door switch The MIU lights the RH rear door symbol. |
| Trunk (Bus from TWICE) | OPEN CLOSED |
TWICE | Lid switch The MIU lights the boot lid symbol. |
| Steering Wheel Position | Left Hand Drive (LHD) Right Hand Drive (RHD) |
TWICE | Control module programming. MIU uses the information to indicate an open door on the pictogram, driver/passenger door. |
| Information Display Lamp | ON OFF |
SID | The MIU lights the Info Display indicator lamp in the event of a text message. |
| Rheostat Value | 0-100 % | SID | Rheostat control module input The MIU uses information on the rheostat setting to control the brightness of the instrument lighting. |
| Rheostat Night Panel, Filtered | 0-100 % | SID | Rheostat control module input reduced by a fixed value. |
| NIGHT PANEL | ON OFF |
SID | The MIU turns off the lighting of certain instruments and displays. |
| Display Lighting | 0-100 % | SID | The MIU uses the information to control the display lighting. |
| Light intensity in cabin | lux | SID | The MIU uses the information to control the brightness of indicator lamps. |
| CHECK ENGINE Light | ON OFF |
ECM | Internal diagnosis. |
| SHIFT UP Lamp | ON OFF |
ECM | Wheel speed, front right (wire from ABS) |
| CRUISE Lamp | ON OFF |
ECM | Cruise Control function |
| Turbo Gauge | 0-255, no unit | ECM (petrol) | Current air mass per combustion. |
| Fuel Used | 0-65535 ml | ECM | Fuel injection function. |
| Engine RPM | 0-7000 RPM | ECM | Crankshaft position sensor |
| Coolant temperature | -40-215°C | ECM | Coolant temperature sensor |
| Glow indicator lamp | ON OFF |
ECM (diesel) | Coolant temperature sensor |
| Selector lever Position | P, R, N, D, 3, 2, 1 | TCM | Selector lever position sensor. |
| CHECK GEARBOX Lamp | ON OFF |
TCM | Internal diagnosis. |
| SPORT | ON OFF |
TCM | The button and oil temperature sensor and not limp-home or WINTER |
| WINTER | ON OFF |
TCM | The button and oil temperature sensor and not limp-home |
| Wheel speed RL | 0-300 km/h | TC/ABS | Wheel speed sensor RL |
| ABS lamp | ON/OFF | TC/ABS | Internal diagnostics |
| TCS OFF lamp | ON/OFF | TC/ABS | Switch, internal diagnostics |
| TCS lamp | ON/OFF | TC/ABS | Traction Control |
| Diagnostics communication | - | DICE/Diagnostic tool | Control module should be live and the bus leads intact. |