Engine Management
System
Revised on: Jun 2020
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Overview
After studying this chapter, you should be able to:
• Describe the operating features of On-board Diagnosis I / II.
• Describe the process of communication within the On-Board
Diagnostic system of a modern vehicle.
• Describe the constructional features and operational characteristics
of an engine control unit.
• Describe the operation and features of current diesel engine
management systems.
• Explain the relationship between sensors, microcomputer and
actuators.
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On-Board Diagnostic (OBD) Systems
• The primary goal of OBD systems is to detect and report system
malfunctions.
• The Malfunction Indicator Lamp (MIL) will illuminate when a failure
which could cause vehicle emission to exceed their designated
standard.
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AT3002FP Engine Technology & Powertrain Management
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OBD-I (On-Board Diagnostic System,
Generation 1)
• OBD-I systems were first used in 1988.
• Monitoring critical emission-related parts and systems.
• Illuminates a malfunction indicator if a defect was found.
• Most OBD-I systems used flash codes to display DTCs.
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OBD-I (On-Board Diagnostic System,
Generation 1)
• The codes were displayed with the MIL.
• The codes were displayed by jumping across terminals at a diagnostic
data link connector (DLC).
• Step by- step diagnostic procedures for identifying the exact fault.
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AT3002FP Engine Technology & Powertrain Management
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OBD-I (On-Board Diagnostic System,
Generation 1)
OBD-I was a step in the right direction, but it had several faults/flaws.
• It monitored few systems.
• Had a limited number of Diagnostic Trouble Codes (DTCs).
• DTCs were not standardized, so each manufacturer had its own.
• Allowed a limited use of serial data.
• Most manufacturers required a specific scan tool and procedure.
• The names used to describe a component varied across the
manufacturers and their model vehicles.
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AT3002FP Engine Technology & Powertrain Management
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OBD-II (On-Board Diagnostic System,
Generation 2)
According to the guidelines of OBD-II, all
vehicles have the following:
• A universal diagnostic test connector, known
as the data link connector (DLC), with
dedicated pin assignments.
• A standard location for the DLC.
• A standard list of diagnostic trouble codes
(DTCs).
• A standard communication protocol.
• The use of common scan tools on all vehicle
makes and models.
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Operating Features of On-Board Diagnosis
• Multiplexing, also called in-vehicle
networking, provides efficient
communications between vehicle
systems.
• Multiplexing relies on one wire that
allows many systems to communicate
instead of many wires.
• A multiplex wiring system uses a serial
data bus that connects different
computers or control modules together.
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Data Link Connector
• The connector has 16 pins that are arranged in
two rows and are numbered consecutively.
• The connector is “D”-shaped and has guide keys
that allow the scan tool to only be installed one
way.
• Using a standard connector and designated pins
allows data retrieval with any scan tool designed
for OBD-II.
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Connect the OBD-II Scanner to DLC
• DLC connectors are supposed to be located on the driver’s side of the
cabin, below the dashboard.
• Some DLCs, however, have been located on the passenger side of the
cabin, centre console or behind the ashtray.
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What the OBD Scanner Can Perform?
• Retrieve/Erase Diagnostics Trouble Codes (DTCs).
• Monitor system operational data.
• Reprogram the vehicle’s electronic control modules.
• Perform systems diagnostic tests.
• Display appropriate service information, including electrical diagrams.
• Display Technical Service Bulletins (TSBs).
• Display troubleshooting instructions.
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Diagnostic Trouble Codes (DTCs) / Fault Codes
• Active codes - is any system code that is
currently active.
• Inactive (historic) codes - Inactive codes are
codes that have been previously logged into
the system. Although no longer active they
have not been cleared.
• Clear codes - Only inactive codes can be
cleared from a chassis electronic system.
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OBD-II DTCs Explained
• DTCs, also known as fault codes, typically are made up of a (1) letter
followed by four (4) numbers.
• So each code has a total of five (5) alphanumeric characters.
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