Controller Area Network (Can)
The CAN bus is a high speed broadcast network between the instrument pack, the ECM, the EAT ECU and the ABS ECU, allowing fast exchange of data between the components every few microseconds.
The bus comprises two wires which are identified as CAN Low (L) and CAN High (H). The wires are twisted together to minimise the electromagnetic interference (noise) produced from the CAN messages.
To prevent message errors from electrical reflections, 120ohm resistors are incorporated into the CAN wire terminals of the ECM, ABS ECU, EAT ECU and the instrument pack.
CAN messages consist of a signal which is simultaneously transmitted, in opposite phase, on both wires. CAN L switches between 2.5 and 1.5 volts, while CAN H switches between 2.5 and 3.5 volts. This causes a potential difference between the two lines to switch between 0 volt (logic 1) and 2 volts (logic 0) to produce the digital signal message.
In the event of CAN bus failure, any of the following symptoms may be observed:
- Tachometer, speedometer and temperature gauge will fail to operate
- CAN controlled warning lamps will be inoperative.