2.2 CAN Bus Diagnosis Opel Vectra C

2.2.1 High Speed CAN Bus Topology

The high speed CAN bus has a linear design and is looped through the individual control units. Exceptions to this are the EHPS control unit and the AHL control unit, which are linked by a stub cable. The maximum high speed CAN bus configuration is shown in the following illustration. The network topology of other vehicle configurations can be determined using the circuit diagram.

The following associations can be derived from this for diagnosis purposes:

1. 1. Examined from the diagnosis plug end, communication takes place via the CIM, YRS, ABS, (EHPS, AHL), TCM and ECM.
2. 2. For example, if the CAN bus is interrupted between the YRS and the ABS, the Tech 2 can only communicate with the CIM. The YRS is different, since it has no self-diagnosis and can therefore not be individually selected using the Tech 2. The other control units behind the separation point are still operational, but can no longer communicate with the tester, the CIM and the YRS. The relevant communication error codes are stored in the control unit fault memories.
3. 3. Disconnecting the control unit plugs from the EHPS control unit only stops communication with the EHPS control unit. All other control units can communicate with the Tech 2 and each other when the ignition is switched on. Appropriate communication error codes are also stored in the fault memories in this case.
4. 4. A total failure is indicated by the following symptoms: the engine will not start, because the starter is not actuated. A flashing SVS lamp does not indicate a total failure but an immobilizer problem. Malfunction indicator lamp for ABS / TC active. No speed display and no rpm display. The fuel level indicator shows empty but the fuel lamp does not flash. All other instrument panel indicators may be operational. The selector lever does not indicate any position.

2.2.2 Mid Speed CAN Bus Topology

The mid speed CAN bus has a linear design and is looped through the individual control units. The mid speed CAN bus is shown with all available control units in the following illustration. Depending on the configuration, only some of the control units shown below are installed in the vehicles. The network topology of other vehicle configurations can be determined using the circuit diagram. Because of the linear design of the mid speed CAN bus, the same rules apply as for the high speed CAN bus when line breaks occur, i.e. interruptions to the CAN bus line or disconnecting a control unit plug causes loss of communication with all downstream control units.

The following indications can be derived from this for diagnosis purposes:

1. 1. It is clearly evident in the ALDL plug that the relevant pins are not occupied if no mid speed CAN bus is installed.
2. 2. If a general mid speed CAN bus failure occurs, the following symptoms can be expected: the display is on, but the ECC is off and cannot be operated. The radio can be switched on but only the start page appears in the display.

2.2.3 Low Speed CAN Bus Topology

The low speed CAN bus has a double ring design, i.e. the CAN bus signal can be received by the control units from two sides. The network topology shown in the following shows the maximum low speed CAN bus configuration. The network topology of other vehicle configurations can be determined from the circuit diagram.

The following associations can be derived from this for diagnosis purposes:

1. 1. If a line break occurs, the control units can still communicate with each other, since the CAN bus signal can be transmitted to the control units via the intact side of the ring. A general CAN communication failure only occurs if a second breaks occurs within a ring.
2. 2. If the low speed CAN bus fails because of an earth contact, for example, no display will be active in the instrument cluster and the low beam headlight is activated as an emergency indicator when the ignition is switched on. In this case, no signals can be detected on the low speed CAN bus.
3. 3. The two sub-rings are connected to each other via the BCM. Disconnecting the wiring harness plug behind the BCM separates the two sub-rings. This arrangement can be used to limit faults as follows. For example, if there is a CAN high lead ground contact in the REC area, the entire low speed CAN bus is out of action. Disconnecting the BCM plug would make the dashboard sub-ring operational again and communication could be reestablished between the tester and the CIM, SDM, IPC and DIS. However, if there is a ground contact in the dashboard sub-ring, disconnecting the BCM plug would not reestablish communication between the tester and the control units, but the body sub-ring would be operational again and could perform functions.
4. 4. If there was a general CIM failure, the tester cannot communicate with the low speed CAN bus because the diagnosis connection is looped through the CIM.