IN−26 − INTRODUCTION HOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS 2. SYMPTOM CONFIRMATION AND DIAGNOSTIC TROUBLE CODE CHECK The diagnostic system in the LEXUS LX470 fulfills various functions. The first function is the Diagnostic Trouble Code 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 the 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, the problem areas can be narrowed down quickly and troubleshooting can be performed effectively.
Diagnostic functions are incorporated in the following systems in the LEXUS LX470. In diagnostic trouble code check, it is very important to determine whether the problem indicated by the diag- nostic trouble code 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 diagnostic trouble code is directly related to the problem symptom or not. For this reason, the diagnostic trouble codes should be checked before and after the symptom confirmation to determine the current conditions, as shown in the table below.
If this is not done, it may, depending on the case, result in unnecessary troubleshooting for normally operating systems, thus making it more difficult to locate the problem, or in repairs not pertinent to the problem. Therefore, always follow the procedure in correct order and perform the diagnostic trouble code check. DIAGNOSTIC TROUBLE CODE CHECK PROCEDURE 2000 LEXUS LX470 (RM745U) 26 Author : Date:
System Diagnostic Trouble Code Check Input Signal Check (Sensor Check) Diagnostic Test Mode (Active Test) Engine Automatic Transmission Active Hight Control Suspension & Adaptive Variable Suspension ABS & Vehicle Skid Control (VSC) & Brake Assist (BA) System Power Tilt and Power Telescopic Steering Column Supplemental Restraint System Cruise Control System Engine Immobiliser System Multiplex Communication System (with Check Mode) (with Check Mode) Diagnostic Trouble Code Check (Make a note of and then clear) Confirmation of Symptoms Diagnostic Trouble Code Check Problem Condition Diagnostic Trouble Code Display Problem symptoms exist Same diagnostic trouble code is displayed Problem is still occurring in the diagnostic circuit Normal code is displayed The problem is still occurring in a place other than in the diagnostic circuit (The diagnostic trouble code displayed first is either for a past problem or it is a secondary problem) No problem symptoms exist The problem occurred in the diagnostic circuit in the past Normal Code Display Problem symptoms exist Normal code is displayed The problem is still occurring in a place other than in the diagnostic circuit No problem symptoms exist Normal code is displayed The problem occurred in a place other than in the diagnostic circuit in the past