Toyota training course t852 engine control systems sec01

Technician Handbook
874 Engine Control Systems II

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Technician Handbook
874 Engine Control Systems II

Diagnostic Tools and
Resources

There are many troubleshooting “tools” that can be used to accurately
identify and troubleshoot driveability problems. These include:
•  Previous troubleshooting experience
•  Use of the OBD self-diagnostic system
•  Service Literature – Technical Information System (TIS), Repair
Manuals, Electrical Wiring Diagrams, and Technical Service
Bulletins
•  Techstream
There are also other resources at your disposal for those
extraordinary situations where your best attempts fail to resolve the
customer concerns:
•  Technical Assistance hotline
•  Area office assistance; STSs, FTSs, and FPEs
With these resources available to you, even the most difficult
customer concerns can be resolved while maintaining high standards
for customer satisfaction.

Previous Troubleshooting
Experience

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Your experience is one of the best resources you have. Depending on
the symptom or customer description of the driveability concern, you
can often eliminate many sub-systems from your diagnostic
investigations. It is important to note, however, this does not mean
that troubleshooting is performed in a random manner. In fact, you will
always fix the car faster and with more accuracy when you follow a
systematic diagnostic approach.

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Technician Handbook
874 Engine Control Systems II

Use of the On-Board
Diagnostic System

All ECMs are equipped with an on-board self-diagnostic system (OBD). This
system is capable of detecting shorts and opens in most sensor electrical
circuits and in some actuator circuits. Later models equipped with the OBD II
system can also detect component and system performance. These OBD
systems are an integral part of your troubleshooting process and will weigh
heavily in your diagnostic outcome.

Diagnostic Toolset

The diagnostic toolset consists of the TIS Techstream, also known as the
Techstream or the “Scan Tool.” Depending on the vehicle you are working on
and the nature of the customer concern, this tool is extremely valuable for
gathering large quantities of diagnostic data in a relatively short period of
time. For troubleshooting engine control system concerns, the Techstream
allows you to quickly perform the following functions:
•  Read and define Diagnostic Trouble Codes (DTCs)
•  Display serial data stream containing sensor, actuator, and diagnostic
information
•  Store and playback snapshot data
•  Display OBD II monitor status and results
•  Test sensors and actuators dynamically using Active Tests

General OBD II Scan Tool
or Techstream Procedure

If the Techstream cannot communicate with ECU controlled systems when
connected to DLC3, the ignition switch is ON, and the Techstream is on,
there is a problem on the vehicle side or tool side.
1.  If communication is normal when the Techstream is connected to
another vehicle, inspect the diagnosis data link line (Bus-line) or ECM
(ECU) power circuit of the vehicle.
2.  If communication is still not possible when the Techstream is connected
to another vehicle, the problem is probably in the Techstream itself.
Check the Techstream Operator’s Manual or call Techstream support
for help.

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Technician Handbook
874 Engine Control Systems II

NOTE

How to Proceed with
Troubleshooting
Operation Flow

NOTE

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Perform troubleshooting in accordance with the flowchart. The
flowchart is an outline of basic troubleshooting procedures. Confirm
the troubleshooting procedures for the circuit you are working on
before beginning troubleshooting. Refer to the Introduction section
of the Repair Manual (RM) for more information.
1.  Vehicle Brought to Workshop
2.  Customer Problem Analysis
a.  Ask the customer about the conditions and environment
when the problem occurred.
3.  Inspect Battery Voltage
a.  Standard voltage is between 11 and 14V. Refer to the
Repair Manual (RM) for vehicle specifications.
b.  If the battery voltage is below 11V, recharge or replace the
battery before proceeding.

4.  Health Check
5.  Symptom Confirmation and DTC (and Freeze Frame Data)
Check
a.  Visually check the wire harnesses, connectors and fuses
for open and short circuits
b.  Warm up the engine to the normal operating temperature
c.  Confirm the problem symptoms and conditions, and check
for DTCs. If DTC output, proceed to step 5. If NO DTC
output, proceed to step 6.
See the Repair Manual (RM) for symptom simulation methods and
more information.

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Technician Handbook
874 Engine Control Systems II
How to Proceed with
Troubleshooting
Operation Flow
(cont’d)

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6.  DTC Chart
a.  Check the results obtained in step 4. Then find the output
DTC in the DTC chart within the Repair Manual (RM).
Look at the “Trouble Area” column for a list of potentially
malfunctioning circuits and/or parts.
7.  Problem Symptoms Chart

a.  Check the results obtained in step 4. Then find the
problem symptoms in the problem symptoms table within
the Repair Manual (RM). Look at the “Suspected Area”
column for a list of potentially malfunctioning circuits and/
or parts.
8.  Circuit Inspection or Part Inspection
a.  Identify the malfunctioning circuit or part.
9.  Adjust, Repair, or Replace
Adjust, repair or replace the malfunctioning circuit or parts.
10.  Confirmation Test
a.  After the adjustment, repairs or replacement, confirm that
the malfunction no longer exists. If the malfunction does
not reoccur, perform a confirmation test under the same
conditions and in the same environment as when the
malfunction occurred the first time.

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Technician Handbook
874 Engine Control Systems II

DTC Check
Operation Flow

In the DTC check, it is very important to determine whether the
problem indicated by the DTC either:
1) still occurs, or 2) occurred in the past but has returned to normal.
In addition, the DTC should be compared to the problem symptom
to see if they are related. For this reason, DTCs should be checked

before and after confirmation of symptoms (i.e., whether or not
problem symptoms exist) to determine current system conditions, as
shown in the flowchart.
Never skip the DTC check. Failing to check DTCs may, depending
on the case, result in unnecessary troubleshooting for systems
operating normally or lead to repairs not related to the problem.
Follow the procedures listed in the flowchart in the correct order.
The flowchart shows how to proceed with troubleshooting using the
DTC check. Directions from the flowchart will indicate how to
proceed either to DTC troubleshooting or to the troubleshooting of
each problem symptom.

NOTE

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Refer to the Introduction section of the Repair Manual (RM) for more
information.

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Technician Handbook
874 Engine Control Systems II

DTC Information

If the DTCs are output after the DTC check procedure is completed, use
the Repair Manual (RM) for the DTC diagnostic procedure.
There is a lot of important information in the DTC troubleshooting sections

of the Repair Manual (RM), such as the system description, monitor
description, monitor strategy, typical enabling conditions, typical
malfunction thresholds, wiring diagram, and inspection procedure. Carefully
studying this information before beginning diagnosis may help you to better
understand the issue and its cause.
•  The Description portion provides an overview of the system operation.
•  The Monitor Description portion provides an overview of the monitor
operation.
•  The Monitor Strategy portion provides information on related DTCs,
required sensors/components to operate (main and related),
frequency of operation (continuous or once per driving cycle), duration
of operation, MIL operation, and sequence of operation.
•  The Typical Enabling Conditions portion provides information on
specific conditions necessary for the monitor to operate, such as
DTCs that cannot be present, system statuses, battery voltage, and
other important conditions.
•  The Typical Malfunction Thresholds portion provides information on
what will cause the monitor to fail and a DTC to set.
•  The Wiring Diagram portion provides a thorough wiring diagram of the
system and components.
•  The Inspection Procedure portion provides the procedure for
diagnosing the cause of the DTC.

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Technician Handbook
874 Engine Control Systems II

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