Actron KAL9620A - Manual (Page 5)

9620 Professional OBD II Scan Tool 5
Section 1: Vehicle Computer Systems
1.1 Introduction
This section describes the engine computer control system, types of sensors and how
the computer controls engine fuel delivery, idle speed and timing. Additional information
may be found in the technical support books at your local library or auto parts store. The
more known about the computer system, the easier the problem can be diagnosed.
Computer controls were originally installed on vehicles to meet federal government
regulations for lower emission levels and improved fuel economy. This began in the early
1980’s when basic mechanical systems were no longer able to accurately control key
engine parameters. A computer could be programmed to control the engine under various
operating conditions, making the engine more reliable. While these early systems were
very limited in scope of their diagnostics, providing only 10-14 trouble codes, they did help
guide the vehicle repair process.
In 1994, manufacturers began equipping vehicles with a new class of computer technology
which puts more processing power under dash than ever before. It is called On-Board
Diagnostics version II, or OBD II. It is required on all vehicles sold in the US beginning
January 1, 1996 (though most domestic manufacturers introduced it earlier than required),
and offers increased system monitoring and diagnostic information. This new system stores
a library of more than 650 general trouble codes and another approximately 400
manufacturer-specific codes, all of which can be accessed with the scan tool. These codes
cover Body Systems (B-Codes), Chassis Systems (C-Codes), Communications Codes
(U-Codes), and Powertrain Systems (P-Codes). Now, basic terms are standardized and
all generic codes will share a common format and terminology that manufacturers and the
Society of Automotive Engineers (SAE) designed.
The OBD II Professional Scan Tool performs OBD II functions on ALL makes of OBD II
compliant vehicles from 1996 and up.
1.1.1 What The Computer Controls
The main control areas of the vehicle computer are fuel delivery, idle speed, spark advance,
and emissions controls. Some on-board computers may also control the transmission,
brakes, and suspension systems as well.
1.1.2 What Has Not Changed
A computer-controlled engine is very similar to the older, non-computerized engine. It is still
an internal combustion engine with pistons, spark plugs, valves, and camshaft(s). The ignition,
charging, starting, and exhaust systems are very similar as well. Test and repair of these
systems are the same as before. The technical manuals for these components provide
instruction on how to perform the tests. Additionally, compression gauges, vacuum pumps,
engine analyzers, and timing lights will continue to be used.
1.1.3 Computer Control System
The vehicle on-board computer, or Powertrain Control Module (PCM), is the “heart” of the
system. It is sealed in a metal box and connected to the rest of the engine by a wiring
harness. The PCM is commonly located in the passenger compartment, behind the
dashboard (kick panel position), although some manufacturers locate the PCM in the
engine compartment. The PCM is programmed by the factory. The program is a complex
list of lookup tables and instructions telling the computer how to control the engine based
on various driving conditions. It does this using sensors to monitor what is happening and
then provide feedback through a network of switches and actuators throughout the vehicle.