Important: An understanding of the following ideas and theories is required before
performing any diagnostic procedures.
• Basic theory of electricity, understand the meaning of voltage
(volts), current (amps) and resistance (ohms). • Understand the affects an open or a shorted wire can have on a
circuit. • Able to read and understand a wiring schematic.
Troubleshooting Procedure
Use the following seven step procedure when diagnosing an electrical system concern. Refer to Strategy Based Diagnostic Flow in General Information for a visual diagram of the following procedure.
Verify Customer Concern, Check the Problem, #1
Verify the correct normal operating behavior of the system also verify that the customer complaint is a valid failure of the system. Use any of the following resources to validate the complaint.
| • | Vehicle road test. |
| • | Review the system operation in the owners manual. |
| • | Check an identical vehicle. |
| • | Review the circuit descriptions in the service manual. |
These questions should be asked: When and where does problem occur? Do all related systems operate properly? How does the problem occur? How often does the problem occur? How long has the condition existed / did it ever work?
Preliminary Checks, #2
The goal of this step is to establish if the complaint is visually obvious and accumulate enough data to properly search for a bulletin. The initial checks may vary due to the complexity of the system and may include:
| • | Identify parts of the system that work properly, review the system's schematic. |
| • | Checking for open fuses, visual inspection for unplugged connectors and checking terminals for damage and tightness. |
| • | Investigating the vehicle's service history. |
When performing the preliminary checks observe the unusual such as noise, vibration/feel, smell.
This step will save time and labor. REMEMBER, it is essential to understand how a circuit should work before trying to figure out why it doesn't. After understanding how a circuit should operate, read the schematic again, this time keeping in mind what has been learned by operating the circuit.
Perform Published Diagnostic System Checks, #3
System checks exist for all electrical systems and consist of two types.
| • | Diagnostic System Check, this table is used for checking various vehicle control modules for any DTC's stored by the vehicle's control modules. |
| • | System Check, this table is used to operate the system and determine if a abnormal condition is present. |
Performing a system check will provide a systematic approach to narrowing down the possible cause of a system fault.
Check for Bulletins, #4
Checking the Technical Service Bulletins and utilizing the Techline equipment for any bulletin information.
Stored DTCs, #5.1
After performing the diagnostic system check follow the DTC diagnostic tables in the service manual.
Symptoms, No DTCs, #5.2
After performing the system check follow the symptom diagnostic tables in the service manual.
No Published Diagnostics, #5.3
Analyze the complaint and utilize the wiring schematics and circuit description to develop a plan for the diagnosing the complaint.
Intermittent, #5.4
Utilize the electrical intermittent information in the service manual.
Operating as Designed, #5.5
If the complaint can not be verified, ensure that the vehicle is tested and is operating as designed. To ensure that customer satisfaction is maintained, verify the complaint under the conditions described by the customer before releasing the vehicle.
Isolate the Root Cause, #6
A properly performed diagnostic check should isolate the root cause of the complaint.
Repair and Verify Completeness of Repair, #7
Once proper diagnosis has been performed and documented, a thorough repair procedure is performed to fix the complaint. To confirm that the repair has addressed the complaint, perform the appropriate system check. If the complaint is still present, re-examine the complaint, review the first four steps of your strategy based diagnostics carefully.
Important: Also verify the complaint under the conditions described by the customer before releasing the vehicle. The verification of the repair in the form of a working test is the only way the repair process can be considered complete, this test should either be a road test or performance test in the service bay.
