Diagnosis and Repair Workflow

Diagnosis and Repair Work Flow

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

Get the detailed information from the customer about the symptom (the condition and the environment when the incident/malfunction occurred) using the "DIAGNOSTIC WORKSHEET".


GO TO 2.

2. CHECK DTC*1

1 Check DTC*1.
2 Perform the following procedure if DTC*1 is displayed.
- Record DTC*1 and freeze frame data*2. (Print them out with SDT or GST.)
- Erase DTC*1. (Refer to [DTC Index: ECM] DTC Index ECM.)
- Study the relationship between the cause detected by DTC*1and the symptom described by the customer. (Symptom Matrix Chart 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*1 is displayed
Symptom is described, DTC*1 is displayed: GO TO 3.
Symptom is described, DTC*1 is not displayed
Symptom is described, DTC*1 is not displayed: GO TO 4.
Symptom is not described, DTC*1 is displayed: GO TO 5.
Symptom is not described, DTC*1 is displayed
ERROR! Unknown action!Symptom is not described, DTC*1 is displayed: GO TO 5.

3. CONFIRM THE SYMPTOM

Try to confirm the symptom described by the customer (except MIL ON).

Diagnosis Work Sheet is useful to verify the incident.

Connect SDT to the vehicle in "Data list" mode and check real time diagnosis results.

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.

DIAGNOSIS WORK SHEET is useful to verify the incident.

Connect SDT to the vehicle in "Data list" mode and check real time diagnosis results.

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*1, and then make sure that DTC*1 is detected again.

At this time, always connect SDT to the vehicle, and check diagnostic results in real time on "Data list".

If two or more DTCs*1 are detected, refer to [DTC Inspection Priority Chart: ECM] ECM and determine trouble diagnosis order.

NOTE:
- Freeze frame data*2 is useful if the DTC*1 is not detected.
- Perform Overall Function Check if DTC Confirmation Procedure is not included on Service Manual. This simplified check procedure is an effective alternative though DTC*1 cannot be detected during this check.
If the result of Overall Function Check is NG, it is the same as the detection of DTC*1 by DTC Confirmation Procedure.

Is DTC*1 detected?
Yes
GO TO 8.
No
Check according to [Service Information for Electrical Incident: Intermittent Incident] Service Information for Electrical Incident: Intermittent Incident.

6. PERFORM BASIC INSPECTION

Perform [Basic Inspection] Basic Inspection.


GO TO 7.

7. DETECT MALFUNCTIONING SYSTEM BY SYMPTOM MATRIX CHART

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 DIAGNOSTIC PROCEDURE

Inspect according to Diagnostic Procedure of the system.

NOTE:
The Diagnostic Procedure in Section 1A described based on open circuit inspection. A short circuit inspection is also required for the circuit check in the Diagnostic Procedure. For details, refer to Circuit Inspection in [Service Information for Electrical Incident: How to Check Terminal] Service Information for Electrical Incident: How to Check Terminal.

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 [SDT Reference Value in Data List Mode] SDT Reference Value in Data List Mode , [ECM Terminal and Reference Value] ECM Terminal and Reference Value.

9. REPAIR OR REPLACE THE MALFUNCTIONING PART

1 Repair or replace the malfunctioning part.
2 Reconnect parts or connectors disconnected during Diagnostic Procedure again after repair and replacement.
3 Check DTC. If DTC is displayed, erase it, refer to [DTC Index: ECM] DTC Index ECM.


GO TO 10.

10. FINAL CHECK

When DTC was detected in step 2, perform DTC Confirmation Procedure or Overall 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.

OK or NG
NG (DTC*1 is detected)
OK:
1 Before returning the vehicle to the customer, make sure to always erase unnecessary DTC*1 in ECM and TCM (Transmission Control Module). (Refer to [DTC Index: ECM] DTC Index ECM.)
2 If the completion of SRT is needed, drive vehicle under the specific driving pattern. Refer to [DTC Index: ECM] DTC Index ECM.
3 INSPECTION END
NG (Symptom remains)
NG (DTC*1 is detected): GO TO 8.
NG (Symptom remains): GO TO 6.
OK

*1: Include 1st trip DTC.

*2: Include 1st trip freeze frame data.

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 an incident. 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 come on steady 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