CCD Bus Testing

Using DRB-II tester, a bus problem will show up in one of 3 ways. Despite passing automatic bus test, a NO RESPONSE message may be displayed rather than an expected value on the DRB-II. It is impossible to use DRB-II until reason for NO RESPONSE message is found and corrected. A NO RESPONSE message can be caused by:

• a bus wire open or poorly connected at a module
• ground or power supply is missing at certain modules
• ignition is turned off and body controller has timed out

A major bus failure can cause anything from an ENGINE NO START CONDITION to a blank message screen on Electronic Vehicle Information Center (EVIC) head. The automatic bus test will not complete or allow access to further system tests at this point and Red light on DRB-II will come on. A major bus failure can be caused by:

• Short To Ground
• Short To Battery Voltage
• Short To 5 Volts
• Bus "+" & Bus "-" Shorted Together

Critical bus messages preventing bus from operating properly are:

• NO TERMINATION
• BIAS LEVEL TOO HIGH
• BIAS LEVEL TOO LOW
• NO BUS BIAS
• BUS - OPEN
• BUS + OPEN
• BUS + & BUS - OPEN
• NOT RECEIVING BUS MESSAGES CORRECTLY

DRB-II will display any of these messages on display screen and then go to the next level of testing with no Red light. The only interference will come when trying to access a module directly related to or causing bus failure. A NO RESPONSE message will then appear.