System Interfaces

System Interfaces Description

The CAN bus, introduced on 99MY petrol vehides, provides the communication link between the ECM and the TCM. Inputs and outputs to and from each control module are transmitted via two twisted wire connections, CAN high and CAN low. The CAN bus allows more engine data to be passed to the TCM which, on earlier vehicles, would require a number of additional hardwired connections. The additional engine data is used by the TCM to give improved transmission quality and allows the TCM to operate in a greater number of default modes in the event of sensor failure. Inputs and outputs on the CAN communicaUon bus are listed in the table that follows.
Inputs from ECM
- CAN version identifier
- Emissions (OBDII) control
- Engine IAT
- Engine speed
- Engine speed fault flag
- ECT
- Engine torque
- Engine torque fault flag
- Friction torque
- Maximum engine torque
- Reduced engine torque
- Road speed
- Status of engine speed torque reduction
- Throttle position

Outputs to ECM
- Calculated gear
- Diagnostic information
- Emission (OBDII) fault status
- Engine torque reduction request
- Gear position switch information
- Output shaft speed
- Mode information
- Shift information
- TCC lock-up solenoid

There are five CAN diagnostics, a fault is detected if:
1. The ignition supply is greater than 9V and no signal or an invalid signal has been received by the TCM.
2. The ignition supply is greater than 9V, and the engine speed is greater than 460 rpm or less than 128 rpm and no CAN messages have been received by the TCM.
3. The ignition supply is greater than 9V and the throttle angle, engine speed, torque signal, ECT, road speed, IAT or altitude information is out or range, contains an error flag or incorrect flag.
4. The ignition supply is greater than 9V and there is a continuity fault with CAN low or CAN high.
5. The road speed is greater than 3.11 mph and the ratio of road speed to output shaft speed exceeds a threshold ratio.

For the diagnostic table, please refer to the individual codes (i.e. P1705, P1841, P1842, P1843 or P1881).

If the above table does not include details of the following enabling conditions: - intake air and engine coolant temperature, vehicle speed range, and time after engine start-up then the state of these parameters has no influence upon the execution of the monitor.