Controller Area Network (CAN) Bus

AUTOMATIC GEARBOX - JATCO

DESCRIPTION AND OPERATION

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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 minimise the electromagnetic interference (noise) produced by the CAN messages.

To prevent message errors from electrical reflections, 120

Ω

 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.

In the event of a CAN bus failure any of the following symptoms may be observed:

l

Transmission defaults to 4th gear

l

Torque converter lock-up control is disabled

l

Transmission of torque reduction message to the ECM is inhibited.

CAN Bus Switching

EAT ECU CAN Messages
The following table lists CAN message inputs and outputs from and to the EAT ECU.

Inputs

Outputs

Actual engine torque

Cooling request

Engine coolant temperature

Current/Target gear

Engine friction

Gear selector lever position

Engine speed

Gear shift in progress

Engine speed signal error

Gearbox fault status

Engine torque error

Torque reduction request

Ignition switch status

Gearbox MIL Status

Actual engine torque

Gear shift mode

Estimated engine torque

Throttle angle (driver demand)

Torque reduction status

Engine MIL status

Hill descent activity status