- Preliminary Inspection
Preliminary ChecksPerform the following steps:
1. Conduct a thorough visual inspection
2. Review the service history
3. Detect unusual sounds or odors
4. Gather diagnostic trouble code information in order to achieve an effective repair.
Check Bulletins and Other Service Information This should include videos, newsletters, and Pulsat programs.
Service Information System Checks
A system may not be supported by one or more DTCs. System checks verify the proper operation of the system. This will lead the technician in an organized approach to diagnostics.
Service Diagnostics (Paper and Electronic)
1. DTC Stored - Follow the designated DTC Table exactly to make an effective repair.
2. No DTC Select the symptom from the symptom tables and follow the diagnostic paths or suggestions to complete the repair, or refer to the applicable component/system check.
3. No Matching Symptom - Analyze the complaint. Develop a plan for diagnostics. Utilize the wiring diagrams and theory of operation.
4. Intermittents - Conditions that are not always present are intermittent. In order to resolve Intermittents, perform the following steps:
4.1. Observe the history DTCs, the DTC modes and, the freeze frame data.
NOTE: Call technical assistance for similar cases where repair history may be available. Combine the technician knowledge with efficient use of the available service information.
4.2. Evaluate the symptoms and conditions described by the customer.
4.3. Use a check sheet or other method in order to identify the circuit or electrical system component.
4.4. Follow the suggestions for intermittent diagnosis found in the service documentation.
4.5. The Tech 1, Tech 2 and Fluke 87 scan tools have data capturing capabilities that can assist in detection of Intermittents.
5. Vehicle operates as designed/No trouble found
6. Call technical assistance for similar cases where repair history may be available. Combine technician knowledge with efficient use of the available service information.
6.1. This condition exists when the vehicle is found to operate normally.
6.2. The condition described by the customer may be normal. Verify against another vehicle that is operating normally.
6.3. The condition may be intermittent. Verify the complaint under the conditions described by the customer before releasing the vehicle.
BASIC KNOWLEDGE AND TOOLS
To use the Powertrain Management section most effectively, a general understanding of basic electrical circuits and circuit testing tools is required. You should be familiar with wiring diagrams, the meaning of voltage, ohms, amps, the basic theories of electricity, and understand what happens in an open or shorted wire.
To perform system diagnosis, the use of a Scan tool Diagnostic Computer or equivalent scan tool is required. A test light, ohmmeter, digital voltmeter with 10 megohms impedance, vacuum gauge, and jumper wires are also required. Become acquainted with the special tools and their use before attempting to diagnose a vehicle. Special tools which are required for system service are illustrated in Tools and Equipment. Tools and Equipment
VISUAL / PHYSICAL UNDERHOOD INSPECTION
Perform a careful visual and physical underhood inspection when performing any diagnostic procedure or diagnosing the cause of an emission test failure. This can often lead to repairing a problem without further steps. Use the following guidelines when performing a visual and physical inspection:
^ Inspect all vacuum hoses for the following conditions:
- Correct routing
- Pinches
- Cuts
- Disconnects
^ Inspect hoses that are difficult to see beneath the air cleaner, A/C compressor, generator, etc.
^ Inspect all wires in the engine compartment for the following items:
- Proper connections
- Burned or chafed spots
- Pinched wires
- Contact with sharp edges
- Contact with hot exhaust manifolds This visual and physical inspection is very important. Preform the inspection carefully and thoroughly.
DIAGNOSTIC PREPARATIONS
All of the Diagnostic procedures have specific conditions under which each test is to be performed. Basic conditions that apply to all tests are:
- VCM and engine grounds are clean and tight.
- Battery B+ cables are clean and tight at the battery and all junction points.
- Battery in good condition and fully charged.
- Adequate fuel in the fuel tank.
- Fuel is uncontaminated.
- Service components in good condition (Fuel Filter, Spark Plugs)
Read each test procedure carefully to determine additional test conditions.
DIAGNOSTIC INFORMATION
The System Diagnostic Tables under Computers and Control Systems / System Diagnosis are designed to locate a faulty circuit or component through logic based on the process of elimination. The charts are prepared with the requirement that the vehicle functioned correctly at the time of assembly and that there are no multiple failures. Testing and Inspection
There is a continual self-diagnosis on certain control functions. This diagnostic capability is complemented by the diagnostic procedures contained in this manual. The language for communicating the source of a malfunction is a system of diagnostic trouble codes. When a malfunction is detected by the VCM, a diagnostic trouble code is set and the Malfunction Indicator Lamp (MIL) "Service Engine Soon" is illuminated on some applications.