NOTE: 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 customer's 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 result of vibration caused by the road during driving, the problem can never be determined as long as the symptom 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 effected 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.

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 cause of the problem and check whether or not the malfunction occurs.
  NOTE: Applying strong vibration to relays may open a relay.
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 Vibration Method
    Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
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 device. Check whether not the malfunction occurs.
NOTE:
- 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.

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.

Safety Warning

Symptom Simulation

Use the Manual With the Right Hardware

When to See a Mechanic

Rather have a pro handle this?