Initial Inspection and Diagnostic Overview
TROUBLESHOOTING DESCRIPTIONTroubleshooting of electronic control systems for which the scan tool can be used follows the basic outline described below. Furthermore, even in systems for which the scan tool cannot be used, part of these systems still follow this outline.
TROUBLESHOOTING CONTENTS
1. STANDARD FLOW OF DIAGNOSTIC TROUBLESHOOTING
The main procedures for diagnostic troubleshooting are shown.
2. SYSTEM OPERATION AND SYMPTOM VERIFICATION TESTS
If verification of the trouble symptoms is difficult, procedures for checking operation and verifying trouble symptoms are shown.
3. DIAGNOSTIC FUNCTION
The following diagnostic functions are shown.
- Method of reading diagnostic trouble codes
- Method of erasing diagnostic trouble codes
- Input inspection service points
4. INSPECTION CHART FOR DIAGNOSTIC TROUBLE CODES
5. INSPECTION PROCEDURE FOR DIAGNOSTIC TROUBLE CODES
Indicates the inspection procedures corresponding to each diagnostic trouble code. (Refer to HOW TO USE THE INSPECTION PROCEDURES later in this article for help on how to read the inspection charts.)
6. INSPECTION CHART FOR TROUBLE SYMPTOMS
If there are trouble symptoms, even though the results of inspection using the scan tool show that all diagnostic trouble codes are normal, inspection procedures for each trouble symptom will be found by means of this chart.
7. INSPECTION PROCEDURE FOR DIAGNOSTIC SYMPTOM
Indicates the inspection procedures corresponding to each trouble symptoms classified in the Inspection Chart for Trouble Symptoms. (Refer to HOW TO USE THE INSPECTION PROCEDURES later in this article for help on how to read the inspection charts.)
8. SERVICE DATA REFERENCE TABLE
Inspection items and normal judgement values have been provided in this chart as reference information.
9. CHECK AT ECU TERMINALS
Terminal numbers for the ECU connectors, inspection items and standard values have been provided in this chart as reference information.
Terminal Voltage Checks
1. Connect a needle-nosed wire probe or paper clip to a voltmeter probe.
2. Insert the needle-nosed wire probe into each of the ECU connector terminals from the wire side, and measure the voltage while referring to the check chart.
NOTE:
1. Measure voltage with the ECU connectors connected.
2. You may find it convenient to pull out the ECU to make it easier to reach the connector terminals.
3. Checks don't have to be carried out in the order given in the chart.
CAUTION:
Short-circuiting the positive (+) probe between a connector terminal and ground could damage the vehicle wiring, the sensor, the ECU, or all three.
Use care to prevent this!
3. If voltage readings differ from Normal Condition values, check related sensors, actuators, and wiring, then replace or repair.
4. After repair or replacement, recheck with the voltmeter to confirm that the repair has corrected the problem.
Terminal Resistance and Continuity Checks
1. Turn the ignition switch to "OFF".
2. Disconnect the ECU connector.
3. Measure the resistance and check for continuity between the terminals of the ECU harness-side connector while referring to the check chart.
NOTE:
Checks don't have to be carried out in the order given in the chart.
CAUTION:
If resistance and continuity checks are performed on the wrong terminals, damage to the vehicle wiring, sensors, ECU, and/or ohmmeter may occur.
Use care to prevent this!
4. If the ohmmeter shows any deviation from the Normal Condition value, check the corresponding sensor, actuator and related electrical wiring, then repair or replace.
5. After repair or replacement, recheck with the ohmmeter to confirm that the repair has corrected the problem.
10. INSPECTION PROCEDURES USING AN OSCILLOSCOPE
When there are inspection procedures using an oscilloscope, these are listed here.
HOW TO USE THE INSPECTION PROCEDURES
The causes of many problems occurring in electronic circuitry are generally the connectors, components, the ECU and the harnesses between connectors, in that order. These inspection procedures follow this order. They first try to discover a problem with a connector or a defective component.
HARNESS INSPECTION
Check for an open or short circuit in the harness between the terminals which were defective according to the connector measurements this also includes checking for blown fuses. For inspection service points when there is a blown fuse, refer to "INSPECTION SERVICE POINTS FOR A BLOWN FUSE".
MEASURES TO TAKE AFTER REPLACING THE ECU
If the trouble symptoms have not disappeared even after replacing the ECU, repeat the inspection procedure from the beginning.
CONNECTOR MEASUREMENT SERVICE POINTS
Turn the ignition switch to OFF when connecting and disconnecting the connectors. Turn the ignition switch to ON when measuring if there are no instructions to the contrary.
IF INSPECTING WITH THE CONNECTOR CONNECTED (WITH CIRCUIT IN A CONDITION OF CONTINUITY)
Waterproof Connectors
Be sure to use the special tool (harness connector). Never insert a test probe from the harness side, as this will reduce the waterproof performance and result in corrosion.
Ordinary (non-waterproof) Connectors
Check by inserting the test probe from the harness side. Note that if the connector (control unit, etc.) is too small to permit insertion of the test probe, it should not be forced; use a special tool (the extra-thin probe in the harness set for checking) for this purpose.
IF INSPECTING WITH THE CONNECTOR DISCONNECTED
[When Inspecting a Female Pin]
Use the special tool (inspection harness for connector pin contact pressure in the harness set for inspection). The inspection harness for connector pin contact pressure should be used. The test probe should never be forcibly inserted, as it may cause a defective contact.
[When Inspecting a Male Pin]
Touch the pin directly with the test bar.
CAUTION
At this time, be careful not to short the connector pins with the test probes. To do so may damage the circuits inside the ECU.
CONNECTOR INSPECTION SERVICE POINTS
VISUAL INSPECTION
- Connector is disconnected or improperly connected
- Connector pins are pulled out
- Due to harness tension at terminal section
- Low contact pressure between male and female terminals
- Low connection pressure due to rusted terminals or foreign matter lodged in terminals
CONNECTOR PIN INSPECTION
If the connector pin stopper is damaged, the terminal connections (male and female pins) will not be perfect even when the connector body is connected, because the pins may pull out of the back side of the connector. Therefore, gently pull the wires one by one to make sure that no pins pull out of the connector.
CONNECTOR ENGAGEMENT INSPECTION
Use the special tool (connector pin connection pressure inspection harness of the inspection harness set) to inspect the engagement of the male pins and female pins. [Pin drawing force: 1 N (0.2 lbs.) or more]
HOW TO COPE WITH INTERMITTENT MALFUNCTIONS
Most intermittent malfunctions occur under certain conditions. If those conditions can be identified, the cause will be easier to find.
TO COPE WITH INTERMITTENT MALFUNCTION;
1. Ask the customer about the malfunction
Ask what it feels like, what it sounds like, etc. Then ask about driving conditions, weather, frequency of occurrence, and so on.
2. Determine the conditions from the customer's responses
Typically, almost all intermittent malfunctions occur from conditions like vibration, temperature and/or moisture change, poor connections. From the customer's replies, it should be reasoned which condition is influenced.
3. Use simulation test
In the cases of vibration or poor connections, use the simulation tests below to attempt to duplicate the customer's complaint. Determine the most likely circuit(s) and perform the simulation tests on the connectors and parts of that circuit(s). Be sure to use the inspection procedures provided for diagnostic trouble codes and trouble symptoms.
For temperature and/or moisture conditions related intermittent malfunctions, using common sense, try to change the conditions of the suspected circuit components, then use the simulation tests below.
4. Verify the intermiffent malfunction is eliminated
Repair the malfunctioning part and try to duplicate the condition(s) again to verify the intermittent malfunction has been eliminated.
SIMULATION TESTS
For these simulation tests, shake, then gently bend, pull, and twist the wiring of each of these examples to duplicate the intermittent malfunction.
- Shake the connector up-and-down, and right-and-left.
- Shake the wiring harness up-and-down, and right-and-left.
- Vibrate the part or sensor.
NOTE:
In case of difficulty in finding the cause of the intermittent malfunction, the data recorder function in the scan tool is effective.
INSPECTION SERVICE POINTS FOR A BLOWN FUSE
Remove the fuse and measure the resistance between the load side of the fuse and ground. Set the switches of all circuits which are connected to this fuse to a condition of continuity. If the resistance is almost 0 ohms at this time, there is a short somewhere between these switches and the load. If the resistance not 0 ohms, there is no short at the present time, but a momentary short has probably caused the fuse to blow.
The main causes of a short circuit are the following.
- Harness being clamped by the vehicle body
- Damage to the outer casing of the harness due to wear or heat
- Water getting into the connector or circuitry
- Human error (mistakenly shorting a circuit)