Chapter 24 PowerPoint

Define these Technical Terms using the textbook:

1. data link connector (DLC)

2. diagnostic trouble codes (DTC)

3. freeze frame

4. key-on/engine-off diagnostics

5. malfunction indicator light (MIL)

6. on-board diagnostics

7. OBDII (on-board diagnostics generation two) system

8. scan tool

9. trouble code chart

Answer these discussion questions using the textbook:

1. Where is the data link connector on most makes and models of cars made after 1996?

Read the chapter summary below:

■ On-board diagnostics refers to a vehicle computer’s ability to analyze the operation of its circuits and output data showing any problems.

■ A scan tool is used to communicate with the vehicle’s computers to retrieve trouble codes, display circuit and sensor electrical values, run tests, and give helpful hints for finding problem sources.

■ OBDI and earlier on-board diagnostic systems could check only a limited number of items.

■ OBDII systems are designed to more efficiently monitor the condition of hardware and software that affect emissions. New vehicle diagnostics detect part deterioration and not just complete part failure.

■ If an unusual condition or electrical value is detected, the computer will turn on a malfunction indicator light (MIL) in the dash instrument panel or driver information center.

■ Code conversion means the scan tool is programmed to automatically convert trouble codes into abbreviated words that explain what might be wrong without referring to a service manual.

■ Diagnostic trouble codes (DTCs) are digital signals produced by the computer when an operating parameter is exceeded.

■ The data link connector (DLC) is a multi-pin terminal for reading computer trouble codes or scanning problems.

■ A scan tool freeze frame is a snapshot of operating parameters at the time of a malfunction.

■ OBDII codes contain a letter and a four-digit number.

■ The letter in all OBDII codes indicates the general function of the affected system.

■ The first digit of the number in OBDII codes indicates whether the code is a standard trouble code or a nonuniform code.

■ The second digit of the number in the OBDII code indicates the specific function of the system where the fault is located.

■ The last two digits in the OBDII code refer to the specific fault designation.

■ A wiggle test is done by moving wires and harness connectors while scanning to find soft failures.