Problem: The customer noted that all of the exterior lights were inoperative, the windshield wipers would begin at any time without being activated by the switch and the instrument cluster would intermittently stop working.
Details: The technician tested communication with all of the modules and looked for diagnostic trouble codes (DTCs). He found communication with the body control module (BCM) to be intermittent and no DTCs were present. After looking at the CAN B circuit diagram, he went to the fuse block in the driver’s kick panel and connected a scope to one of the green CAN B bus wires to check for a normal 0 to 5-volt square wave signal. He found that the pattern oscillated between 0 and 7 volts. Next, he began to unplug modules on the CAN B network until a normal communication signal returned (See scope patterns).
Confirmed Repair: In this case, the fuse box in the rear cargo area was defective. The technician replaced the fuse box and the 0 to 5-volt reference returned to the network. This one repair fixed all of the issues the customer was experiencing.
Bad pattern with 0 to 7-volt communication signal
Good pattern with 0 to 5-volt communication signal