July/August 2021

Yellow Channel – Pin 3 Green Channel – Pin 11 It can be seen from this waveform that there is no activity on the network and the voltage is close to ground potential. This issue can occur due to a module internally shorting the network to ground or a wiring fault creating the short circuit. One of the more common areas on a vehicle for wiring problems is the wiring loom where it enters the doors. As faults were present in both the driver and passenger door modules, this was the first area to be investigated. The wiring to both the driver and passenger door was undamaged and disconnecting one door at a time did not resolve the issue. Common failure Another common failure on modern vehicles is the instrument cluster. On this particular vehicle the cluster is relatively easy to remove and disconnect the electrical connector. No issue was found here and with the module disconnected the network did not become active. The next part of the network to be investigated was the 28 AFTERMARKET JULY/AUGUST 2021 TECHNICAL/SNAP-ON www.aftermarketonline.net Fig.5 Fig.7 Fig. 8 climate control module. It was noticed that the CAN signal was intermittently present while the CCM was being removed from the dash. Applying hand pressure to the dashboard resolved the issue, removing the hand from the dash resulted in the fault re-appearing. This is indicative of a wiring fault and in particular a wire(s) shorting against a vehicle ground. The CCM, glovebox, radio and various trim panels were removed to inspect the wiring (see Fig.3). One of the mid-speed CAN Bus network wires was found to be touching a metal bracket behind the radio (see Fig.4 and Fig.5). The wiring was repaired and a foam pad attached to the metal bracket for additional protection against future issues. The CAN network now preformed as expected. Fig.6 shows the expected mid speed CAN Bus data signal, while Fig.7 displays data transfer speed calculated from end of frame Bit (EOF) – 125 Kbits per Second. Finally, Fig.8 shows differential voltage between CAN High and Low – mid speed CAN Bus Network. The fault codes were erased and the vehicle reassembled. A road test was carried out and the vehicle preformed as expected. This repair would have been very difficult without the correct wiring diagram for the vehicle, a scan tool to access the fault codes in each system and an oscilloscope to monitor the CAN bus signal. diagnostics.snapon.co.uk This repair would have been very difficult without the correct wiring diagram, a scan tool to access the fault codes and an oscilloscope ”