May 2021

MAY 2021 AFTERMARKET 29 Case Study – Opel Astra This vehicle wouldn’t start, as terminal 50 on the starter motor solenoid was not receiving current when the ignition key was turned to the start position. Also, there was no communication with the Engine Management control module, Instrument cluster, Anti-Lock Brake Control module or Steering Column Integration module (CIM) using a scan tool. These modules are on the high-speed CAN bus. The vehicle had a flat battery and a technician attempted to start the vehicle unsuccessfully. An oscilloscope was connected to pin 6 and pin 14 of the vehicle Data Link Connector (DLC) to access the high-speed network (see Fig.13). Pin assignment: Pin 4: Chassis ground Pin 5: Signal ground Pin 6: CAN High (ISO 15765) Pin 14: CAN Low (ISO 15765) Pin 16: Constant supply (+12 volts). Referring to Fig.14, the waveform was captured. Testing the resistance of the network showed a short circuit (see Fig.15). As the issue was most likely as a result of a damaged electronic control module each module on the high speed network was disconnected in turn until the network signal returned to the waveform expected. When the Anti-Lock Brake module was disconnected the oscilloscope displayed the waveform as seen in Fig.16. The vehicle now started and the scan tool was capable of communicating with the Engine Control Module, Instrument cluster and the CIM. The network resistance also returned to specification, as seen in Fig.17. Fig.18 illustrates how a basic system such as the starter motor has changed since CAN bus technology has been implemented on vehicles. The start signal from the ignition switch is sent to the Steering Column Module, once processed it is converted to a CAN message and transmitted on the CAN network. The Engine Bay Fusebox uses this message to control the starter motor relay by grounding terminal 85 of the relay winding. This results in the relay contacts closing and supplying current to terminal 50 of the starter motor solenoid. It can be seen that the internal electrical circuit of the starter motor remains unchanged. Pin assignment: 30 – Constant Live 31 – Ground 15 – Ignition on Live 50 – Starter motor solenoid control 86 – Starter motor relay winding supply 85 – Starter motor relay winding ground control 87 – Starter motor relay contacts output. The Gateway is the link between multiple networks. The module can be a separate or part of another module such as an instrument cluster module. Fig.19 shows the high speed Class C CAN network (500 kBits/second), the comfort Class B CAN network (250 kBits/second) and the Lin Bus local network (10 kBits/second) all capable of communicating via the gateway module. Fig 6 Fig 7 Fig 8 Fig 9 Fig 10 Fig 11 Fig 12 Fig 13 Fig 14 Fig 15 Fig 16 Fig 17 Fig 18 Fig 19 Fig 5