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HOMESERVICE MANUALSTOYOTA2004SIENNA XLE LIMITED, AWDREPAIR AND DIAGNOSISGENERAL INFORMATIONOEM GENERAL INFORMATIONINTRODUCTIONHOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMSHOW TO PROCEED WITH TROUBLESHOOTINGSYMPTOM SIMULATION
2004 Toyota Sienna XLE Limited, AWD

Symptom Simulation

2004 Toyota Sienna XLE Limited, AWDSECTION Symptom Simulation
NOTE: The most difficult case in troubleshooting is when no symptoms occur. In such cases, a thorough customer problem analysis must be carried out. Then the same or similar conditions and environment in which the problem occurred in the customer's vehicle should be simulated. No matter how much experience a technician has, or how skilled he may be, if he proceeds to troubleshoot without confirming the problem symptoms, he will tend to overlook something important in the repair operation and make a wrong guess somewhere, which will only lead to a standstill. For example, for a problem which only occurs when the engine is cold, or for a problem which occurs due to vibration caused by the road during driving, etc., the problem can never be determined when the engine is hot or when the vehicle at is a standstill. Since vibration, heat or water penetration (moisture) is a likely cause for the problem which is difficult to reproduce, the symptom simulation tests introduced here are effective measures in a point that the external causes are applied to the vehicle in a stationary condition.

Important points in the symptom simulation test:

In the symptom simulation test, the problem symptoms should be confirmed, and the problem area or parts must also be discovered. To do so, reduce the possible problem circuits according to the symptoms before starting this type of test and have the hand-held tester connected beforehand. After that, carry out the symptom simulation test, judging whether the circuit being tested is defective or normal and also confirming the problem symptoms at the same time. Refer to the problem symptoms table of each system to narrow down the possible causes of the symptom.

  1. VIBRATION METHOD: When vibration seems to be the major cause. 
    1. PART AND SENSOR
      1. Apply slight vibration with your finger to the part of the sensor considered to be the problem cause and check whether the malfunction occurs.
        NOTE: Applying strong vibration to relays may result in open relays.
    2. CONNECTORS
      1. Slightly shake the connector vertically and horizontally.
    3. WIRE HARNESS
      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.

        Fig 1: Checking Malfunction With Vibrations
        G02932857Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  2. HEAT METHOD: If the problem seems to occur when the area in question is heated. 
    1. Heat the component that is the possible cause of the malfunction with a hair dryer or similar object. Check if the malfunction occurs.
      NOTE:
      • Do not heat the components to more than 60°C (140°F) (Temperature is limited to keep the components from being damaged).
        Fig 2: Checking Malfunction With Heat Dryer
        G02932858Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      • Do not apply heat directly to the parts in the ECU.
  3. WATER SPRINKLING METHOD: When the malfunction seems to occur on a rainy day or in high-humidity. 
    1. Sprinkle water onto the vehicle and check if the malfunction occurs.
      NOTE:
      • Never sprinkle water directly onto the engine compartment, but indirectly change the temperature and humidity by spraying a mist of water onto the radiator front surface.
      • Never apply water directly onto the electronic components.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.