Diagnosis and Repair Workflow
Diagnosis and Repair Workflow
Introduction
The engine has an ECM to control major systems such as fuel control, ignition control, idle air control system, etc. The ECM accepts input signals from sensors and instantly drives actuators. It is essential that both input and output signals are proper and stable. At the same time, it is important that there are no malfunctions such as vacuum leaks, fouled spark plugs, or other malfunctions with the engine.
It is much more difficult to diagnose an incident that occurs intermittently rather than continuously. Most intermittent incidents are caused by poor electric connections or improper wiring. In this case, careful checking of suspected circuits may help prevent the replacement of good parts.
A visual check only may not find the cause of the incidents. A road test with SDT (or GST) or a circuit tester connected should be performed. Follow the Work Flow on "Work Flow".
Before undertaking actual checks, take a few minutes to talk with a customer who approaches with a driveability complaint. The customer can supply good information about such incidents, especially intermittent ones. Find out what symptoms are present and under what conditions they occur. A Diagnostic Worksheet like the example on "Worksheet Sample" should be used.
Start your diagnosis by looking for conventional malfunctions first. This will help troubleshoot driveability malfunctions on an electronically controlled engine vehicle.
Work Flow
Overall Sequence
Detailed Flow
1. GET INFORMATION FOR SYMPTOM
1 Get the detailed information from the customer about the symptom (the condition and the environment when the incident/malfunction occurred) using the "Diagnostic Work Sheet".
2 Ask if the customer requests I/M examination.
Malfunction information, obtained
Malfunction information, obtained: GO TO 2.
No malfunction information, but a request for I/M examination
No malfunction information, but a request for I/M examination: GO TO 11.
2. CHECK DTC
1 Check DTC.
2 Perform the following procedure if DTC is displayed.
- Record DTC and freeze frame data. (Print them out with SDT or GST.)
- Erase DTC.
Refer to [On Board Diagnosis Function] On Board Diagnosis Function (Without SDT) or [SDT Function] SDT Function (With SDT).
- Study the relationship between the cause detected by DTC and the symptom described by the customer. (Symptom Table is useful. Refer to [Engine Control System Symptoms: Symptom Matrix Chart] Symptom Related Diagnostic Procedures.)
1 Check related service bulletins for information.
Are any symptoms described and any DTCs detected?
Symptom is described, DTC is detected
Symptom is described, DTC is detected: GO TO 3.
Symptom is described, DTC is not detected
Symptom is described, DTC is not detected: GO TO 4.
Symptom is not described, DTC is detected: GO TO 5.
Symptom is not described, DTC is detected
3. CONFIRM THE SYMPTOM
Try to confirm the symptom described by the customer (except MIL ON).
Also study the normal operation and fail-safe related to the symptom.
Diagnosis Work Sheet is useful to verify the incident.
Verify relation between the symptom and the condition when the symptom is detected.
GO TO 5.
4. CONFIRM THE SYMPTOM
Try to confirm the symptom described by the customer.
Also study the normal operation and fail-safe related to the symptom.
Diagnosis Work Sheet is useful to verify the incident.
Verify relation between the symptom and the condition when the symptom is detected.
GO TO 6.
5. PERFORM DTC CONFIRMATION PROCEDURE
Perform DTC CONFIRMATION PROCEDURE for the displayed DTC, and then make sure that DTC is detected again.
If two or more DTCs are detected, refer to [DTC Inspection Priority Chart: ECM] ECM and determine trouble diagnosis order.
NOTE:
- Freeze frame data is useful if the DTC is not detected.
- Perform Component Function Check if DTC CONFIRMATION PROCEDURE is not included on Service Manual. This simplified check procedure is an effective alternative though DTC cannot be detected during this check.
If the result of Component Function Check is NG, it is the same as the detection of DTC by DTC CONFIRMATION PROCEDURE.
Is DTC detected?
YES
GO TO 10.
NO
Check according to [Service Information for Electrical Incident: Work Flow] Service Information for Electrical Incident: Work Flow.
6. PERFORM BASIC INSPECTION
Perform [Basic Inspection] Basic Inspection.
GO TO 7.
7. DETECT MALFUNCTIONING SYSTEM BY SYMPTOM TABLE
Detect malfunctioning system according to [Engine Control System Symptoms: Symptom Matrix Chart] Symptom Related Diagnostic Procedures based on the confirmed symptom in step 4, and determine the trouble diagnosis order based on possible causes and symptoms.
GO TO 8.
8. DETECT MALFUNCTIONING PART BY DIAGNOSIS PROCEDURE
Inspect according to Diagnosis Procedure of the system.
NOTE:
The Diagnosis Procedure in Section 1A described based on open circuit inspection. A short circuit inspection is also required for the circuit check in the Diagnosis Procedure. For details, refer to [Service Information for Electrical Incident: Work Flow] Service Information for Electrical Incident: Work Flow.
Is a malfunctioning part detected?
YES
GO TO 9.
NO
Monitor input data from related sensors or check voltage of related ECM terminals using SDT. Refer to [ECM Terminal and Reference Value] ECM Terminal and Reference Value , [SDT Reference Value in Data List Mode] SDT Reference Value in Data List Mode.
9. REPAIR OR REPLACE THE MALFUNCTIONING PART
1 Repair or replace the malfunctioning part.
2 Reconnect parts or connectors disconnected during Diagnosis Procedure again after repair and replacement.
3 Check DTC. If DTC is displayed, erase it. Refer to [On Board Diagnosis Function] On Board Diagnosis Function (Without SDT) or [SDT Function] SDT Function (With SDT).
GO TO 10.
10. FINAL CHECK
When DTC was detected in step 2, perform DTC CONFIRMATION PROCEDURE or Component Function Check again, and then make sure that the malfunction have been completely repaired.
When symptom was described from the customer, refer to confirmed symptom in step 3 or 4, and make sure that the symptom is not detected.
Is DTC detected and does symptom remain?
YES-1 DTC is detected: GO TO 8.
YES-2 Symptom remains: GO TO 6.
NO-1 No request for I/M examination from the customer: Before returning the vehicle to the customer, always erase unnecessary DTC in ECM and TCM (Transmission Control Module). Refer to [On Board Diagnosis Function] On Board Diagnosis Function (Without SDT) or [SDT Function] SDT Function (With SDT) and [SDT Function (AT)] Scan Tool Testing and Procedures.
NO-2 I/M examination, requested from the customer: GO TO 11.
11. Prepare for I/M examination
1 Set SRT codes. Refer to [How to Set SRT Code: Description] How to Set SRT Code Description.
2 Erase permanent DTCs. Refer to [How to Erase Permanent DTC] How to Erase Permanent DTC.
INSPECTION END
Diagnostic Worksheet
Description
There are many operating conditions that lead to the malfunction of engine components. A good grasp of such conditions can make troubleshooting faster and more accurate.
In general, each customer feels differently about symptoms. It is important to fully understand the symptoms or conditions for a customer complaint.
Utilize a diagnostic worksheet like the one on the next page in order to organize all the information for troubleshooting.
Some conditions may cause the MIL to illuminate or blink and DTC to be detected. Examples:
- Vehicle ran out of fuel, which caused the engine to misfire.
- Fuel filler cap was left off or incorrectly screwed on, allowing fuel to evaporate into the atmosphere.
Worksheet Sample
