Controller Area Network (CAN) Bus
The CAN bus is a high speed broadcast network between the ECM, instrument pack, ABS ECU and the EAT ECU allowing fast exchange of data between the ECU's 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 minimize the electromagnetic interference (noise) produced by the CAN messages.
To prevent message errors from electrical reflections, 120-ohm resistors are incorporated into the CAN wire terminals of the ECM, instrument pack, ABS ECU and the EAT ECU.
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. See Fig 1 .
In the event of a CAN bus failure any of the following symptoms may be observed:
- Transmission defaults to 4th gear.
- Torque converter lock-up control is disabled.
- Transmission of torque reduction message to the ECM is inhibited.