Introduction: Diagnosis Toyota Sequoia I

USING OBD II SCAN TOOL OR HAND-HELD TESTER

1. Before using the scan tool or tester, the scan tool's instruction book or tester's operator manual should be read thoroughly.
2. If the scan tool or tester cannot communicate with ECU controlled systems when you have connected the cable of the scan tool or tester to DLC3, turned the ignition switch ON and operated the scan tool, there is a problem on the vehicle side or tool side. If communication is normal when the tool is connected to another vehicle, inspect the diagnosis data link line (Busline) or ECU power circuit of the vehicle. If communication is still not possible when the tool is connected to another vehicle, the problem is probably in the tool itself, so perform the Self Test procedures outline in the Tester Operator's Manual.

HOW TO PROCEED WITH TROUBLESHOOTING

Carry out troubleshooting in accordance with the troubleshooting flowchart. Here, only the basic procedure is shown. Details are provided in Diagnostics articles, showing the most effective methods for each circuit. Confirm the troubleshooting procedures first for the relevant circuit before beginning troubleshooting of that circuit.

Scheme 7

Symptom Confirmation And Diagnostic Trouble Code Check

The diagnostic system in the Sequoia 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 Sequoia.

Scheme 8

Diagnostic Trouble Code Check Procedure

Taking into account the points in (Scheme 10), a flow chart showing how to proceed with troubleshooting using the diagnostic trouble code check is (Scheme 11) This flowchart shows how to utilize the diagnostic trouble code check effectively, then by carefully checking the results, indicates how to proceed either to diagnostic trouble code troubleshooting or to troubleshooting of problem symptoms table.

Scheme 9

Scheme 10

Symptom Simulation

The most difficult case in troubleshooting is when there are no problem symptoms occurring. 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 likely cause for problem which is difficult to reproduce, the symptom simulation tests introduced here are effective measures in 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, but 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 symptom simulations (Scheme 12), for each system to narrow down the possible causes of the symptom.

Scheme 11

Diagnostic Trouble Code Chart

The inspection procedure is shown in explaining diagnostic trouble code chart example. This table permits efficient and accurate troubleshooting using the diagnostic trouble codes displayed in the diagnostic trouble code check. Proceed with troubleshooting in accordance with the inspection procedure given in the diagnostic chart corresponding to the diagnostic trouble codes displayed. The engine diagnostic trouble code chart is shown below as an example.

Scheme 12

Problem Symptoms Table

Note. When the problem is not detected by the diagnostic system even though the problem symptom is present, it is considered that the problem is occurring outside the detection range of the diagnostic system, or that the problem is occurring in a system other than the diagnostic system.

The suspected circuits or parts for each problem symptom are shown in the problem symptoms table example. Use Problem Symptoms Tables when included in articles to troubleshoot the problem when a "Normal" code is displayed in the diagnostic trouble code check but the problem is still occurring. Numbers in the table indicate the inspection order in which the circuits or parts should be checked.

Scheme 13

Circuit Inspection

Note. Some articles include figures containing information which when provided can be used in accordance with this procedure.

Scheme 14

Scheme 15

Scheme 16

Scheme 17

Scheme 18

Scheme 19

Scheme 20

Scheme 21

Scheme 22

Scheme 23

Scheme 24

Scheme 25

Scheme 26

Scheme 27

Scheme 28

Scheme 29

Scheme 30

Scheme 31

Scheme 32

1. CONNECTOR AND TERMINAL INSPECTION In most articles for troubleshooting, diagnostic trouble code charts or problem symptom tables are provided for each circuit with detailed inspection procedures. When all the component parts, wire harnesses and connectors of each circuit except the ECU are found to be normal in troubleshooting, then it is determined that the problem is in the ECU. Accordingly, if diagnosis is performed without the problem symptoms occurring, refer to step 8 to replace the ECU. So always confirm that the problem symptoms are occurring, or proceed with inspection while using the symptom simulation method. The instructions "Check wire harness and connector" and "Check and replace ECU" which appear in the inspection procedure, are common and applicable to all diagnostic trouble codes. Follow the procedure outlined in this article whenever these instructions appear. Open Circuit: This could be due to a disconnected wire harness, (Scheme 17), faulty contact in the connector, and a connector terminal pulled out, etc. NOTE: It is rarely the case that a wire is broken in the middle of it. (Scheme 18) Most cases occur at the connector. In particular, carefully check the connectors of sensors and actuators. Faulty contact could be due to rusting of the connector terminals, to foreign materials entering terminals or a deformation of connector terminals. Simply disconnecting and reconnecting the connectors once changes the condition of the connection and may result in a return to normal operation. Therefore, in troubleshooting, if no abnormality is found in the wire harness and connector check, but the problem disappears after the check, then the cause is considered to be in the wire harness or connectors. Short Circuit: This could be due to a contact between wire harness and the body ground or to a short circuit occurring inside the switch, etc. NOTE: When there is a short circuit between the wire harness and body ground, check thoroughly whether the wire harness is caught in the body or is clamped properly.
2. CONNECTOR HANDLING When inserting tester probes into a connector, insert them from the rear of the connector. When necessary, use mini test leads. For water resistant connectors which cannot be accessed from behind, take good care not to deform the connector terminals.
3. CONTINUITY CHECK (OPEN CIRCUIT CHECK) NOTE: Measure the continuity while lightly shaking the wire harness vertically and horizontally. Disconnect the connectors at both ECU and sensor sides. Measure the resistance between the applicable terminals of the connectors. Resistance: 1 Ohm or less.
4. RESISTANCE CHECK (SHORT CIRCUIT CHECK) NOTE: Measure the resistance while lightly shaking the wire harness vertically and horizontally. Disconnect the connectors on both ends. Measure the resistance between the applicable terminals of the connectors and body ground. Be sure to carry out this check on the connectors on both ends. Resistance: 1 M/Ohm or higher.
5. VISUAL CHECK AND CONTACT PRESSURE CHECK NOTE: The terminals should not come out when pulled lightly from the back. When testing a gold-plated female terminal, always use gold-plated male terminal. When the test terminal is pulled out more easily than others, there may be poor contact in that section. Disconnect the connectors at both ends. Check for rust or foreign material, etc. in the terminals of the connectors. Check crimped portions for looseness or damage and check that the terminals are secured in lock portion. Prepare a test male terminal and insert it in the female terminal, then pull it out.
6. CHECK OPEN CIRCUIT For the open circuit in the wire harness (Scheme 25), perform step a (continuity check) or b (voltage check) to locate the section. Check the continuity: Disconnect connectors "A" and "C" and measure the resistance between them. In the case of (Scheme 26): Between terminal 1 of connector "A" and terminal 1 of connector "C", if no continuity (open). Between terminal 2 of connector "A" and terminal 2 of connector "C" means continuity. Therefore, it is found that there is an open circuit between terminal 1 of connector "A" and terminal 1 of connector "C". Disconnect connector "B" and measure the resistance between the connectors. In the case of (Scheme 27): Between terminal 1 of connector "A" and terminal 1 of connector "B1" has continuity. Between terminal 1 of connector "B2" and terminal 1 of connector "C" there is no continuity (open). Therefore, it is found that there is an open circuit between terminal 1 of connector "B2" and terminal 1 of connector "C". Check the voltage: In a circuit in which voltage is applied (to the ECU connector terminal), an open circuit can be checked for by conducting a voltage check. (Scheme 28), with each connector still connected, measure the voltage between body ground and terminal 1 of connector "A" at the ECU 5V output terminal, terminal 1 of connector "B", and terminal 1 of connector "C", in that order. If the results are: 5V: Between Terminal 1 of connector "A" and Body Ground 5V: Between Terminal 1 of connector "B" and Body Ground OV: Between Terminal 1 of connector "C" and Body Ground Then it is found out that there is an open circuit in the wire harness between terminal 1 of "B" and terminal 1 of "C".
7. CHECK SHORT CIRCUIT If the wire harness is shorted to ground as in (Scheme 29), locate the section by conducting a "continuity check with ground". Check for continuity to ground: Disconnect connectors "A" and "C" and measure the resistance between terminal 1 and 2 of connector "A" and body ground. In the case of (Scheme 30): Between terminal 1 of connector "A" and body ground there is continuity (short). Between terminal 2 of connector "A" and body ground there is NO continuity. Therefore, it is found that there is a short circuit between terminal 1 of connector "A" and terminal 1 of connector "C". Disconnect connector "B" and measure the resistance between terminal 1 of connector "A" and body ground, and terminal 1 of connector "B2" and body ground. In the case of (Scheme 31): Between terminal 1 of connector "A" and body ground there is no continuity. Between terminal 1 of connector "B2" and body ground there is continuity (short). Therefore, it is found out that there is a short circuit between terminal 1 of connector "B2" and terminal 1 of connector "C".
8. CHECK AND REPLACE ECU First check the ECU ground circuit. If it is faulty, repair it. If it is normal, the ECU could be faulty, so replace the ECU with a normal functioning one and check that the symptoms disappear. Measure the resistance between the ECU ground terminal and the body ground. Resistance: 1 Ohm or less. Disconnect the ECU connector, check the ground terminals on the ECU side and the wire harness side for bend and check the contact pressure.