Trouble Diagnosis Introduction

TROUBLE DIAGNOSIS


Trouble Diagnosis Introduction


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 leakage, 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 CONSULT-III (or GST) or a circuit tester connected should be performed. Follow the WORK FLOW below.





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. 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 CONSULT-III or GST.)
Erase DTC*1. (Refer to "How to Erase DTC" in Emission-Related Diagnostic Information.)
Study the relationship between the cause detected by DTC*1 and the symptom described by the customer. (Symptom Matrix Chart is useful. Refer to Symptom Related Diagnostic Procedures.)
3. Check related service bulletins for information.
Are any symptoms described and any DTCs detected?
Symptom is described, DTC*1 is displayed GO TO 3.
Symptom is described, DTC*1 is not displayed GO TO 4.
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 WORKSHEET 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.
DIAGNOSIS WORKSHEET 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*1, and then check that DTC*1 is detected again.
If two or more DTCs*1 are detected, refer to Engine Controls 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 10.
No - Check according to Diagnosis Procedure.
6.PERFORM BASIC INSPECTION
Perform Basic Service Procedure.
With CONSULT-III GO TO 7.
Without CONSULT-III GO TO 9.
7.PERFORM SPEC IN DATA MONITOR MODE
With CONSULT-III
Check that "MAS A/F SE-B1", "B/FUEL SCHDL", "A/F ALPHA-B1" and "A/F ALPHA-B2" are within the SP value using "SPEC" in "DATA MONITOR" mode with CONSULT-III. Refer to Inspection Procedure.
Are they within the SP value?
Yes - GO TO 9.
No - GO TO 8.
8.DETECT MALFUNCTIONING PART BY TROUBLE DIAGNOSIS - SPECIFICATION VALUE
Detect malfunctioning part according to Diagnosis Procedure.
Is a malfunctioning part detected?
Yes - GO TO 11.
No - GO TO 9.
9.DETECT MALFUNCTIONING SYSTEM BY SYMPTOM MATRIX CHART
Detect malfunctioning system according to 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 10.
10.DETECT MALFUNCTIONING PART BY DIAGNOSTIC PROCEDURE
Inspect according to Diagnostic Procedure of the system.

NOTE:
The Diagnostic Procedure in EC section 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 How to Perform Efficient Diagnosis For an Electrical Incident.
Is a malfunctioning part detected?
Yes - GO TO 11.
No - Monitor input data from related sensors or check voltage of related ECM terminals using CONSULT-III. Refer to Consult-III Reference Value In Data Monitor Mode, ECM Harness Connector Terminal Layout ECM Terminal and Reference Value.
11.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 "How to Erase DTC" in Emission-Related Diagnostic Information.
- GO TO 12.
12.FINAL CHECK
When DTC was detected in step 2, perform DTC Confirmation Procedure or Overall Function Check again, and then check that the malfunction have been completely repaired.
When symptom was described from the customer, refer to confirmed symptom in step 3 or 4, and check that the symptom is not detected.
OK or NG
NG (DTC*1 is detected) GO TO 10.
NG (Symptom remains) GO TO 6.
- 1. Before returning the vehicle to the customer, always erase unnecessary DTC*1 in TCM
OK
(Transmission Control Module) and ECM. (Refer to "How to Erase DTC" in Introduction OBD-II Function For A/T System One or Two Trip Detection Logic of OBD-II OBD-II Diagnostic Trouble Code (DTC), "OBD-II
Emission-Related Diagnostic Information.)
2. If the completion of SRT is needed, drive vehicle under the specific driving pattern. Refer to "How to Set SRT Code" in Emission-Related Diagnostic Information.
3. INSPECTION END
*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 symptoms. It is important to fully understand the symptoms or conditions for a customer complaint.
Utilize a diagnostic worksheet like the Worksheet Sample below 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

Worksheet Sample: