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Chapter 4 On-Board Diagnostics

(OBD) Basics

Your new MICROSCAN conforms to Global OBD (OBD-II in North America and EOBD in Europe)

standards, and is designed for testing compliant vehicles. This chapter describes Global OBD.

4.1 OBD-II/EOBD Advantages

The advantage of OBD-II and EOBD is the simple “Plug and Play” function:

• Unlike using a manufacturer specific scan tool or vehicle communication software, one does

not have to select the vehicle make, year or model.

• The communication protocol can be automatically detected by the scan tool software.

• Depending on the ECM and amount of parameters selected, data update rates may vary. By

using functions as Custom Data List and Manual Select PID in Service $01, sometimes data

update rates may be higher than with manufacturer specific software. This can be helpful in

finding intermittent signal glitches.

Data and monitors that are not described in the OBD/EOBD standards are filtered out, although

they are selectable.

4.2 Communication Protocols

A communication protocol is a standardized way of data communication between an ECM and a

scan tool.

For OBD-II and EOBD compliant vehicles, the following communication protocols are permitted:

• SAE J1850 PWM (pulse width modulation) and VPW (variable pulse width)

• SAE J1939 HD (heavy duty) OBD

• ISO 9141-2 (K-LINE)

• ISO 14230-2 (keyword protocol 2000)

• ISO 15765-4 (CAN)

The scanner attempts to automatically determine the communication protocol by the vehicle. If the

scan tool is unable to determine the protocol in use, it must be selected from the menu

4.2.1 What is CAN?

Many late-model vehicles have Controller Area Network (CAN) systems, which means the vehicle

control units are linked together in a network and can interchange data. Although some

manufacturers have used CAN for some years to communicate between electronic control

modules (ECMs), it was not always directly connected to the diagnostic connector. In

approximately 2001/2002 for Europe and 2003 for North America, the manufacturers started to

connect the CAN communication lines to the diagnostic connector.

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Blue point Microscan III Manual do Utilizador Página 17