Lexus SC300 / Lexus SC400. Service manual — part 897

HOW TO PROCEED WITH TROUBLESHOOTING

The Engine Control System broadly consists of the sensors, ECU and actuators. The ECU receives signals from
various sensors, judges the operating conditions and determines the optimum injection duration, timing, ignition
timing and idle speed.
In general, the Engine Control System is considered to be a very intricate system to troubleshoot. But, the fact
is that if you proceed to inspect the circuit one by one following the procedures directed in this manual, trouble-
shooting of this system is not complex.
This section explains the most ideal method of troubleshooting and tells how to carry out the necessary repairs.

[1] CUSTOMER PROBLEM ANALYSIS

Using the customer problem analysis check sheet for reference, ask the customer in as much details as
possible about the problem.

[2] CHECK AND CLEAR DIAGNOSTIC CODE (PRECHECK)

Before confirming the problem symptom, first check the diagnostic code and make a note of any malfunc-
tion code which is output, then clear the code.
HINT: Output of the malfunction code indicates that there is a malfunction in the circuit indicated. However,
it does not indicate whether the malfunction is still occurring or occurred in the past and returned to normal.
In order to determine this, the problem symptoms should be confirmed in 4 first and the diagnostic code
be rechecked in [6].
Accordingly, if troubleshooting is begun based on the malfunction code only in diagnostic code check in
[2], it could result in a misdiagnosis, leading to troubleshooting of circuits which are normal and making
it more difficult to locate the cause of the problem.

[3] SETTING THE TEST MODE DIAGNOSIS, [4] PROBLEM SYMPTOM CONFIRMATION, [5] SYMPTOM

SIMULATION
In order to find out the trouble more quickly, set the diagnosis check in test mode and with higher sensing
ability of the ECU, confirm the problem symptoms. If the trouble does not reappear, use the symptom simu-
lation method to make sure the trouble is reproduced.

[6] DIAGNOSTIC CODE CHECK IN TEST MODE

Check the diagnostic code in test mode. If the malfunction code is output, proceed to ”step [8] Diagnostic
Code Chart”. If the normal code is output, proceed to ”step [7] Basic Inspection”.

[7] BASIC

INSPECTION

Carry out basic inspection such as the spark check and fuel pressure check, etc.

[8] DIAGNOSTIC CODE CHART

If the malfunction code is displayed, proceed to inspect the circuit indicated by the chart for each code.

[9] MATRIX CHART OF PROBLEM SYMPTOMS

If the normal code is displayed in the diagnosis in test mode, perform troubleshooting according to the in-
spection order in the Matrix Chart of Problem Symptoms.

[10] PARTS INSPECTION

When the Matrix Chart of Problem Symptoms instructs to check the parts, proceed to parts inspection sec-
tion included in this manual.

[11] CIRCUIT INSPECTION

Determine if the malfunction is the sensor, actuator, wire harness, connector or the ECU.

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ENGINE TROUBLESHOOTING

How to Proceed with Troubleshooting

[12] CHECK FOR MOMENTARY INTERRUPTION

By performing the check for momentary interruption, the place where momentary interruptions or momen-
tary shorts are occurring due to poor contacts can be isolated.

[13] ADJUSTMENT, REPAIR

After the cause of the problem is located, perform adjustment or repairs by following the inspection and
replacement procedures in this manual.

[14] CONFIRMATION TEST

After completing adjustment or repairs, confirm not only that the malfunction is eliminated, but also conduct
a test drive, etc., to make sure the entire Engine Control System is operating normally.

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ENGINE TROUBLESHOOTING

How to Proceed with Troubleshooting

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ENGINE TROUBLESHOOTING

How to Proceed with Troubleshooting

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ENGINE TROUBLESHOOTING

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