38 Auto Brakes Copyright by Goodheart-Willcox Co., Inc. Breakout Boxes Early anti-lock brake systems did not have true self- diagnostics, which required technicians to use a breakout box to fi nd the problem. A breakout box is simply a box con- taining numbered test terminals and a harness designed to mate with a system’s main wiring harness connector. Break- out boxes are designed to allow technicians to use a multi- meter to check voltage and resistance values in a system’s various circuits, Figure 3-27. Th e breakout box is connected to a system’s harness, such as a computer wiring harness connector. Th e meter’s terminals are then plugged into the various numbered terminals to check for proper voltage or Goodheart-Willcox Publisher Figure 3-26. This MaxiSys diagnostic scanner includes waveform meter functionality. OTC Tools Figure 3-27. Breakout boxes are used to diagnose early anti- lock brake systems. Goodheart-Willcox Publisher Figure 3-28. One particular type of scan tool. Always use the proper tool and follow the troubleshooting process carefully. resistance. A manual is used to outline the specifi c test pro- cedures for each problem. Scan Tools Th e scan tool is used to check the operation of anti-lock brake and traction control systems. Th e scan tool is attached to a data link connector, usually the same connector used to retrieve engine and drivetrain information. Th e primary use of the scan tool in brake work is to retrieve trouble codes stored in the anti-lock brake and traction control computer. Th ese trouble codes are stored when a malfunction occurs. Retrieving these codes before performing any tests makes the troubleshooting process much quicker and easier. Scan tools can also be used to operate parts of the anti-lock brake system, such as pumps and solenoids, to check system con- dition. A typical scan tool is shown in Figure 3-28. Th e most obvious use of scan tools is to retrieve trou- ble codes. Many scan tools can be used to perform other diagnostic activities. For instance, scan tools can be used to access the wheel speed sensor input and output readings. Th ese readings can be compared with factory specifi cations to determine whether or not the component is defective. Th e scan tool can also be used to override the control module