Checking the Basics

CHECKING THE BASICS
All troubleshooting must begin by "Checking the Basics". Certain basic faults can be undetectable by the self-diagnostic systems of the fuel and ignition control units and in some cases can actually interfere with the self-checking and fault memory operation.

Fault codes should be retrieved at this time. This will prevent loss of codes in the event of power disruption to the control module, or similar event that could cause loss of codes.

Prior to any teardown, repair or component replacement, the following steps should always be considered:

Battery State of Charge
Batteries in a state of partial discharge can have a dramatic effect on control units and related components.

Positive Battery Cable Integrity
All positive electrical connections must be in perfect condition for trouble-free electronic system operation.

Fuse Integrity
Fuses are employed to prevent possible damage to electrical components and wiring harnesses. The fuses and their connections must be without dynamic resistance. Dynamic resistance can only be checked using the voltage drop method of testing.

Negative Ground Connections
As all electrical circuits are a circle, all negative battery connections must also be checked and verified to be in perfect condition. A poor "common" ground point will cause seemingly unrelated systems to influence one another. High current systems which encounter a poor "common" ground can back feed through other electrical systems causing unusual operation and perhaps premature component failure. As with the positive side of the electrical system, the ground side should be checked dynamically using the voltage drop technique.

Powertrain Cable Attachments
Metal cables attached to the engine or transmission that appear overheated and/or discolored indicate the need to thoroughly test all ground connections.

Power Supply Relays
The system relay as well as its plug connection can be a source of intermittent operation which will not set a fault in control unit fault memory.

Vehicle Sensors
Sensors should be checked statically and dynamically. Physical mounting and condition of the sensor must be assured.

Ignition System
The ignition primary and secondary systems should be inspected for loose connections, damaged insulation, moisture, and corrosion.

Fuel Delivery
Fuel delivery must begin at once when cranking and the pressure in the fuel rails must be within specifications. Fuel pressure retention must be maintained between the fuel pump outlet and the pressure regulator after engine shutdown.

Air/Fuel Ratio
When troubleshooting idle quality or driveability complaints, it is necessary to consider the following:

- Presence of unmetered air leaks
- Evaporative purge system
- Excessive engine oil dilution
- Color and odor of exhaust
- Condition of air and PCV filter
- Condition of air flow meter electrical connections