Communication on the Internal Network

Communication On The Internal Network

CAN communication
ECM (Engine Control Module) sends out and receives the following signals via the network:

Brake Control Module (BCM)
Provides information so that the ECM can determine whether any misfiring is due to road condition or to a fault in the engine management system. Also provides a vehicle speed signal.

Climate Control Module (CCM)
Informs the ECM about A/C selection and requests A/C activation.

Central Electronic Module (CEM)
Is the "main computer" in the network and coordinates required information between other modules. It also controls diagnostic function by connecting the Data Link Connector (DLC) to the network for programming and reading off diagnostic trouble codes (DTCs) and parameters. The CEM also includes the Immobilizer.

Steering Wheel Module (SWM)
Provides information to the ECM that the cruise control is selected and that the driver requests changing the cruise control speed.

Transmission Control Module (TCM)
The Transmission Control Module (TCM) is only implemented in automatic transmission cars.

The following signals are being sent on the network from the ECM and picked up by the TCM:
- Engine load
- Throttle opening
- Response to torque limiting
- Accelerator pedal position
- Cruise control status

The following signals are sent out on the network from the TCM and taken up by the ECM:
- Request for torque limiting step I and II
- Request to light Malfunction Indicator Lamp (MIL)
- Signal for constant idle speed compensation (P/N position)
- Engaged gear

Data Link Connector (DLC) (OBD II)
The serial communication via the Data Link Connector (DLC) is used when reading off the Volvo on-board diagnostic (OBD) system. The Volvo proprietary communication system uses a different protocol e.g. not ISO 9141-2, which is only used for legislated communication with a Scan tool. The ECM communicates serially with the Data Link Connector (DLC).