NOTE: The most difficult case in troubleshooting is that no problem symptoms occurs. In such cases, a thorough customer problem analysis must be carried out. Then simulate the same or similar conditions and environment in which the problem occurred in the customer's vehicle. 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 with the engine hot condition or the vehicle at 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 found out. To do so, narrow down the possible problem circuits according to the symptoms before starting this test and have a 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.

VIBRATION METHOD: When vibration seems to be the major cause.
1. PART AND SENSOR
  1. Apply slight vibration with a finger to the part of the sensor considered to be the problem cause and check that the malfunction occurs.
    
    Fig 1: Inspecting Sensor/Wire Harness By Vibration Method
    Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  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 to be checked thoroughly.
HEAT METHOD: When the problem seems to occur when the suspect area 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.
CAUTION:
- Do not heat to more than 60° C (140° F) (Temperature is limited so as not to damage the components).
- Do not apply heat directly to the parts in the ECU.
WATER SPRINKLING METHOD: When the malfunction seems to occur on a rainy day or in a high-humidity condition.
1. Sprinkle water onto the vehicle and check if the malfunction occurs.
CAUTION:
- Never sprinkle water directly onto the engine compartment, but indirectly change the temperature and humidity by applying water spray onto the radiator front surface.
- Never apply water directly onto the electronic components.

Chapter Navigation

Return to Chapter: How To Troubleshoot Ecu Controlled Systems

Safety Warning

Symptom Simulation

Use the Manual With the Right Hardware

When to See a Mechanic