This step in diagnosis includes confirmation of the problem and routine mechanical and electrical engine checks.
Confirmation of the customer concern is an excellent place to begin any diagnosis. It is important to gather and analyze as much information as the customer can supply and, if the check engine warning lamp is on, to retrieve and record the diagnostic codes.
The conditions of the battery and charging system are critical to the proper operation of the electronic control system. Both should be routinely checked by measuring cranking and engine running battery voltage prior to proceeding with diagnosis.
Depending on the problem or driveability symptom indicated, the following checks should be conducted under the hood:
• Inspection of the engine's mechanical condition (i.e., audible cranking rhythm and visual ignition secondary condition).
• Brief inspection of accessible electrical, vacuum and air induction system duct connections.
• Locate and inspect the condition of the ECU main grounds.
• Inspect for leakage in the EGR and PCV valves.
• Inspect for unwanted fuel entering the intake manifold from the EVAP system.
The entire routine quick check procedure can be performed in less than ten minutes and will often save an hour or more of unnecessary diagnostic time.
Use of the Self Diagnostic System Once you are satisfied that there are no routine problems causing the customer concern, use of the self diagnostic system is in order. This system is available on all P7 and TCCS equipped engines and is capable of indicating if certain faults exist in ECU monitored circuits.
The P7 systems have limited diagnostic capabilities and can only display seven diagnostic codes, including a system normal code. This system will only indicate a fault if the circuit is open or shorted to ground.
Late model TCCS systems have more sophisticated diagnostics which monitor more ECU related circuits with as many as 21 or more diagnostic codes. The latest TCCS ECUs have some special capabilities which make them more useful in diagnosis and prevent the check engine warning light from becoming a source of customer dissatisfaction.
• To allow the diagnostic system to find more system faults, the electrical parameters which the ECU uses to set a diagnostic code are altered to find sensor performance faults like oxygen sensor degradation.
• Some minor TCCS system fault codes will set a diagnostic code in the ECU keep alive memory but will not turn on the check engine light and unnecessarily alarm the customer.
• To prevent false indication of certain system faults, some ECUs are programmed to use a two-trip detection logic which prevents the check engine light from illuminating, or certain codes from setting, until the problem has duplicated itself twice, with a key off cycle in between.
• Some ECUs have a special diagnostic TEST mode which causes the ECU to narrow its diagnostic parameters for the technician, thereby, making troubleshooting intermittent problems easier.
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