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Toyota Camry
 Service Manual
Introduction How to troubleshoot ecu controlled systems
Symptom simulation

The most difficult case in troubleshooting is when no problem symptoms occur. In such cases, a thorough customer problem analysis must be carried out. A simulation of the same or similar conditions and environment in which the problem occurred in the customers vehicle should be carried out. No matter how much skill or experience a technician has, troubleshooting without confirming the problem symptoms will lead to important repairs being overlooked and lead to mistakes or delays.

For example: With a problem that only occurs when the engine is cold or occurs as a result of vibration caused by the road during driving, the problem can never be determined if the symptoms are being checked on a stationary vehicle or a vehicle with a warmed−up engine.

Vibration, heat or water penetration (moisture) is difficult to reproduce. The symptom simulation tests below are effective substitutes for the conditions and can be applied on a stationary vehicle.

Important points in the symptom simulation test: In the symptom simulation test, the problem symptoms as well as the problem area or parts must be confirmed.

First, narrow down the possible problem circuits according to the symptoms. Then, connect the tester and carry out the symptom simulation test, judging whether the circuit being tested is defective or normal.

Also, confirm the problem symptoms at the same time. Refer to the problem symptoms table for each system to narrow down the possible causes.

1. VIBRATION METHOD: When vibration seems to be the major cause



1. Apply slight vibration with a finger to the part of the considered to be the cause of the problem and check whether or not the malfunction occurs.

Applying strong vibration to relays may open relays.


1. Slightly shake the connector vertically and horizontally.


1. Slightly shake the wire harness vertically and horizontally.

The connector joint and fulcrum of the vibration are the major areas that should be checked thoroughly.

Vibration method

2. HEAT METHOD: If the problem seems to occur when the area in question is heated.

a. Heat the component that is the possible cause of the malfunction with a hair dryer or similar device. Check if the malfunction occurs.

NOTICE: Do not heat to more than 60 C (140 F). Exceeding this temperature may damage components.

Do not apply heat directly to the parts in the ECU.

Heat method

3. WATER SPRINKLING METHOD: When the malfunction seems to occur on a rainy day or in high−humidity.

a. Sprinkle water onto the vehicle and check if the malfunction occurs.


  • Never sprinkle water directly into the engine compartment.
  • Indirectly change the temperature and humidity by applying water spray onto the front of the radiator.

  • Never apply water directly onto the electronic components.

HINT: If the vehicle has or had a water leakage problem, the leakage may have damaged the ECU or connections. Look for evidence of corrosion or shorts. Proceed with caution during water tests

Water sprinkling method

4. HIGH ELECTRICAL LOAD METHOD: When a malfunction seems to occur when electrical load is excessive.

a. Turn on all the electrical loads including the heater blower, headlights, rear window defogger, etc., and check if the malfunction occurs.

High electrical load method

    More about How to troubleshoot ecu controlled systems:

    General information

    How to proceed with troubleshooting

    Customer problem analysis

    Symptom confirmation and diagnostic trouble code

    Symptom simulation

    Diagnostic trouble code chart

    Problem symptoms table

    Circuit inspection

    Electronic circuit inspection procedure

    Toyota Camry Service Manual / Introduction / How to troubleshoot ecu controlled systems / Symptom simulation

    Toyota Camry Service Manual


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