How could anybody give you a diagram when you didn't provide the year make and
model. Most cars you start with a resistance test, should be 60 ohms, if that checks
out, look for voltage on both the negative and positive bus lines, both should be about
2.5 volts. Added together they should add up to 5 volts. If that checks out check for
short to ground. Then unplug one module atl a time until communications returns.
That is if you lost communications which you failed to mention if you lost
communication or just have codes.