Chapter 24 On-Board Diagnostic and Scan Tools

On-Board Diagnostics

Term for a vehicle computer's ability to analyze the operation or its circuits and to output data identifying any problems found.

Actuator Diagnostic Test

Test that enables a technician to heck if actuators are working. It uses a scan tool to order a vehicle's computer to energize specific output devices with the engine on or off.

Malfunction Indicator Light (MIL)

Amber-colored light in an instrument cluster, commonly called a Check Engine or Service Engine Soon light, used to indicate that a problem exists in a vehicle's computer control system. It is also a generalized term used for any instrument cluster light used to indicate a problem in a system.

Operating Parameter

An acceptable maximum or minimum electrical value saved in permanent computer memory chips.

Freeze Frame

Can tool snapshot of all vehicle monitored components when a trouble code occurs or when triggered during a drive.

On-Board Diagnostics Generation One (OBD I)

Classification referring to any computer control system installed on vehicles built prior to 1996.

Soft Failure

Computer system failure, also called intermittent failure, that only occurs under certain conditions. It stores in the memory for 30-50 keystarts or warm-ups.

Trouble Code Chart

Diagnostic aid that lists the problem encountered for each code

Fault Designation

Last two digits of an alphanumeric trouble code that pinpoints exactly which component or circuit of a vehicle system might be at fault, as well as the type of problem.

Datastream Value

Voltage, degree, and other values that come to the ECM from sensors and actuators in the form of analog and digital signals.

Switch Diagnostic Test

A test that involves activating various switches while using a scan tool to determine if the switch is working normally.

Hard Failure

An always present computer system failure that sets a diagnostic code as soon as the ignition key is turned to run.

Key-On/Engine-On Diagnostic

Diagnostics performed with the engine running at full operating temperature.

Key-On/Engine-Off Diagnostic

Diagnostics performed with the ignition key turned to the on position, but the engine not running.

Diagnostic Trouble Code (DTC)

Digital signal produced and stored by a computer when an operating parameter is exceeded. It can be used to determine where a malfunction is located in a computer-controlled system.

Failure Record

ECM documentation of the number of times (keystarts or warm-ups) a particular trouble code has occurred.

Scan Tool

Electronic tool, usually hand held, that is used to read and interpret diagnostic codes and engine sensor information.

On-Board Diagnostics Generation Two (OBD II)

Enhanced diagnostic system required on 1996 and newer vehicles. Protocol also called for standardization of codes, data link connectors and terminology.

Adaptor

On a scan tool, an adapter is a connector that allows the scan tool connector to fit a vehicle's data link connector if pin configurations differ.

Wiggle Test

Physically moving wires and connectors while the engine is off or running to locate broken wires or other causes of intermittent problems.

Assembly Line Diagnostic Link (ALDL)/Data Link Connector (DLC)/Diagnostic Connector

Plug-in connector used to link the scan tool to a vehicle computer. It allows the scan tool to access vehicle computer data.

Trouble Code Conversion

Process of a scan tool automatically converting a number code into abbreviated words that explain a potential problem.

General Circuit Failure

Specific type of computer system failure caused by a component that has no output or has an output that is out of specification.

Improper Range/Performance Failure

Specific type of computer system failure that occurs when a sensor or actuator produces values slightly lower or higher than normal.

Low-Input Failure

Specific type of computer system failure that produces voltage, current, or signal frequency below normal operating parameters.

High-Input Failure

Specific type of computer system failure that results when the signal reaching the ECM has more voltage, more current, or a higher frequency than normal.

Prompt

Step-by-step instruction, programmed into a scan tool circuitry or cartridge, that tells how to input vehicle information and run diagnostics.