Symptom Confirmation and Diagnostic Trouble Codes
SYMPTOM CONFIRMATION AND DIAGNOSTIC TROUBLE CODEHINT:
- The diagnostic system in the LEXUS SC430 has various functions.The first function is the Diagnostic Trouble Code (DTC) Check in which a malfunction in the signal circuits to the ECU is stored in code in the ECU memory at the time of occurrence, to be output by a technician during troubleshooting. Another function is the Input Signal Check which checks if the signals from various switches are sent to the ECU correctly. By using these check functions, possible areas of the problem can be narrowed down quickly and troubleshooting can be performed effectively. The diagnostic functions are incorporated in the following systems in the LEXUS SC430.
- In the DTC check, it is very important to determine whether the problem indicated by the DTC is still occurring or occurred in the past but returned to normal at present. In addition, it must be checked in the problem symptom check whether the malfunction indicated by the DTC is directly related to the problem symptom or not. For this reason, the DTC should be checked before and after the symptom confirmation to determine the current conditions. If this is not done, it may, depending on the case, result in an unnecessary troubleshooting for normally operating systems, in making it more difficult to detect the problem area, or in repairing impertinences to the problem. Therefore always follow the procedures in the correct order and perform the DTC check.
- A flow chart showing how to proceed with the troubleshooting using the diagnostic trouble code (DTC) check is shown. This flow chart shows how to utilize the DTC check effectively. Then by carefully checking the results, this chart indicates how to proceed either to the DTC troubleshooting or to the troubleshooting of problem symptoms table.
The problem is still occurring in a place other than the diagnostic circuit (The DTC displayed first is either for a past problem or it is a secondary problem).
HINT: The most difficult case in troubleshooting is that there occurs no problem symptoms. 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 so long as the symptoms are confirmed 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 stopped condition.
Important points in the symptom simulation test:
In the symptom simulation test, the problem symptoms should, of course, be confirmed, and the problem area or parts must also be found out. To do this, narrow down the possible problem circuits according to the symptoms before starting this test and connect a tester 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.
a. 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.
HINT: Applying strong vibration to relays may result in open relays.
b. CONNECTORS
1. Slightly shake the connector vertically and horizontally.
c. WIRE HARNESS
1. Slightly shake the wire harness vertically and horizontally.
The connector joint, fulcrum of the vibration, and body through portion are the major areas to be checked thoroughly.
2. HEAT METHOD: When the problem seems to occur when the suspect area is heated.
a. 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 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.
3. WATER SPRINKLING METHOD When the malfunction seems to occur on a rainy day or in a high-humidity condition.
a. 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 applying water spray onto the radiator front surface.
- Never apply water directly onto the electronic components.
HINT: If a vehicle is subject to water leakage, the leaked water may contaminate the ECU. When testing a vehicle with a water leakage problem, special caution must be taken.
4. OTHERS: When the 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.