HOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS GENERAL INFORMATION



  1. TROUBLESHOOTING PROCEDURES


    • The troubleshooting procedures consist of diagnosis procedures for when a DTC is stored and diagnosis procedures for when no DTC is stored. The basic idea is explained in the following table.

      Procedure Type Details Troubleshooting Method
      DTC Based Diagnosis The diagnosis procedure is based on the DTC that is stored.

      The malfunctioning part is identified based on the DTC detection conditions using a process of elimination.

      The possible trouble areas are eliminated one-by-one by use of the intelligent tester and inspection of related parts.

      Symptom Based Diagnosis

      (No DTCs stored)

      The diagnosis procedure is based on problem symptoms.

      The malfunctioning part is identified based on the problem symptoms using a process of elimination.

      The possible trouble areas are eliminated one-by-one by use of the intelligent tester and inspection of related parts.

    • Vehicle systems are complex and use many ECUs that are difficult to inspect independently. Therefore, a process of elimination is used, where components that can be inspected individually are inspected, and if no problems are found in these components, the related ECU is identified as the problem and replaced.

    • It is extremely important to ask the customer about the environment and the conditions present when the problem occurred (Customer Problem Analysis). This makes it possible to simulate the conditions and confirm the symptom. If the symptom cannot be confirmed or the DTC does not recur, the malfunctioning part may not be identified using the troubleshooting procedure, and the ECU for the related system may be replaced even though it is not defective. If this happens, the original problem will not be solved.

    • In order to prevent endless expansion of troubleshooting procedures, the troubleshooting procedures are written with the assumption that multiple malfunctions do not occur simultaneously for a single problem symptom.

    • To identify the malfunctioning part, troubleshooting procedures narrow down the target by separating components, ECUs and wire harnesses during the inspection. If the wire harness is identified as the cause of the problem, it is necessary to inspect not only the connections to components and ECUs but also all of the wire harness connectors between the component and the ECU.

  2. DESCRIPTION

    System data and the Diagnostic Trouble Codes (DTCs) can be read from the Data Link Connector 3 (DLC3) of the vehicle. When the system seems to be malfunctioning, use the intelligent tester to check for a malfunction and perform repairs.

  3. DATA LINK CONNECTOR 3 (DLC3)


    1. A01VI1HE01
      Text in Illustration
      *a Front view of DLC3

      The vehicle ECU uses the ISO 15765-4 communication protocol. The terminal arrangement of the DLC3 complies with SAE J1962 and matches the ISO 15765-4 format.

      Terminal No. (Symbol) Terminal Description Condition Specified Condition
      7 (SIL) - 5 (SG) Bus "+" line During transmission Pulse generation
      4 (CG) - Body ground Chassis ground Always Below 1 Ω
      5 (SG) - Body ground Signal ground Always Below 1 Ω
      16 (BAT) - Body ground Battery positive Always 11 to 14 V
      6 (CANH) - 14 (CANL) CAN bus line Ignition switch off* 54 to 69 Ω
      6 (CANH) - 4 (CG) HIGH-level CAN bus line Ignition switch off* 200 Ω or higher
      14 (CANL) - 4 (CG) LOW-level CAN bus line Ignition switch off* 200 Ω or higher
      6 (CANH) - 16 (BAT) HIGH-level CAN bus line Ignition switch off* 6 kΩ or higher
      14 (CANL) - 16 (BAT) LOW-level CAN bus line Ignition switch off* 6 kΩ or higher

      Note

      *: Before measuring the resistance, leave the vehicle as is for at least 1 minute and do not operate the ignition switch, any other switches, or the doors.

      If the result is not as specified, the DLC3 may have a malfunction. Repair or replace the harness and connector.

    2. Connect the cable of the intelligent tester to the DLC3, turn the ignition switch on and attempt to use the tester. If the display indicates that a communication error has occurred, there is a problem either with the vehicle or with the tester.

      Tech Tips


      • If communication is normal when the tester is connected to another vehicle, inspect the DLC3 of the original vehicle.

      • If communication is still not possible when the tester is connected to another vehicle, the problem may be in the tester itself. Consult the Service Department listed in the tester's instruction manual.


    • FOR USING INTELLIGENT TESTER
      • Before using the intelligent tester, read the tester operator's manual thoroughly.

      • If the tester cannot communicate with the ECU controlled systems when connected to the DLC3 with the ignition switch in the on position and the tester turned on, there is a problem on the vehicle side or tester side.


        1. If communication is possible when the tester is connected to another vehicle, inspect the diagnosis data link line (bus (+) line), CANH and CANL lines, and the power circuits for the vehicle ECUs.

        2. If communication is still not possible when the tester is connected to another vehicle, the problem is probably in the tester itself. Perform the Self Test procedure outlined in the tester operator's manual.