General
This document uses examples to describe physical CAN bus diagnosis facilities using the Tech31 and Tech32 testers. In principle, the measurements described in the following can also be carried out using commercially available multimeters and oscilloscopes. The examples that are shown have been derived from the CAN bus system introduced in the Vectra C. A detailed description of the CAN bus systems introduced in the Vectra C can be found in "Vectra C - New Technical Features" (LU Link) and "Vectra C - Diagnosis Strategy" (LU Link).
Physical CAN Bus Diagnosis
CAN bus communication in vehicles with CAN bus networks must always be checked if problems occur that cannot be clearly identified. Individual system diagnosis should only be carried out if it has first been established that the CAN bus communication is working correctly. Performing diagnosis on individual systems when there are communication problems on the CAN bus can lead to erroneous diagnoses. Physical problems on the CAN bus network lead to communication errors between CAN bus participants. Self-diagnosis of the control units concerned usually stores communication errors in the fault memory, which can be read out using the Tech 2. However, if self-diagnosis troubleshooting using the control units and the Tech 2 is fruitless, physical diagnosis can be performed on the CAN bus using the methods described in this document.
- Diagnosis based on network topologies
- Resistance measurements on high-speed and mid-speed CAN bus
- Level measurement on low-speed CAN bus.
- Oscilloscope measurements
Important: In networked CAN bus systems, fault codes can also be set in other systems that are not directly associated with the faulty system. Fault codes can also be set as a result of troubleshooting/repair.
1.3 CAN Bus Measuring Points on Vectra C
Communication between individual control units in the Vectra C takes place via the CAN bus. Exceptions to this are the Infotainment devices, which communicate with the tester via the conventional Keyword2000 and Keyword 82 protocols. The Tech 2 with the CANdi acts as a separate control unit on the CAN bus network that communicates with other control units. For this reason, all three CAN bus sub-networks in the Vectra C are directly accessible via the ALDL diagnosis connector.
| Pin | Signal | Pin | Signal |
|---|---|---|---|
| 1 | LS-CAN High | 9 | --- |
| 2 | --- | 10 | --- |
| 3 | MS - CAN High | 11 | MS - CAN Low |
| 4 | Terminal 31 / Ground | 12 | K-line 3, car phone, GPS, navigation, telem. |
| 5 | Terminal 31 / Signal Ground | 13 | --- |
| 6 | HS - CAN High | 14 | HS - CAN Low |
| 7 | --- | 15 | --- |
| 8 | K-line 4, telematics, radio | 16 | Terminal 30, power supply |
Important: Suitable measuring adapters must always be used when taking measurements in the ALDL connector. The KM 609 electronics kit contains suitable pin adapters. During measurement it must also be noted that no CAN bus communication can take place if CAN bus lines are short-circuited, which will lead to operational malfunctions that may cause the vehicle to stop.