Checking the Basics

WARNING: Review Service Precautions. Improper handling could cause activation of the airbag(s) and lead to injuries!

All Troubleshooting must begin by "Checking the Basics".
Certain basic faults can be undetectable by the diagnostic equipment and in some cases can actually interfere with Control Unit self-checking and Fault Memory operation.

Low battery voltage for example can cause erroneous faults to set in Control Unit Fault Memories or can cause a system to go "Fail Safe" without setting a fault in memory. On the other hand System Fault Memories are cleared whenever the Control Unit or the battery is disconnected. Therefore, all fault memories should be read and printed prior to any vehicle power interruption or troubleshooting.

Complaint Verification
Whenever possible the repairing technician should personally verify the complaint. Having experienced the malfunction himself, the technician is less likely to try to repair nonexistent faults.

Malfunction Verification
Today's sophisticated automotive systems are easily misunderstood which can lead to repairs that attempt to force a particular system to perform in a way that it was never intended to operate. Therefore the troubleshooting technician must compare the system operation to the nominal system operation as described in Description and Operation and electrical Diagrams. Prior to teardown, the technician is also encouraged to compare the problem vehicle system operation with a known good vehicle.

The following list serves to remind the troubleshooter that todays (and tomorrow's) Advanced Automotive Systems are still dependent on basic requirements. 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 Supplemental Restraint System (SRS) control units and related components.

Positive Battery Cable Integrity
All B+ connections must be in perfect condition for trouble-free electronic system operation. Refer to electrical Diagrams for B+ interconnects.

Fusible Link Integrity
Fusible links are employed to prevent possible damage to electrical components and wiring harnesses. These links and their connections must be without dynamic resistance.

NOTE: Dynamic resistance can only be checked using the voltage drop method of testing.

Negative Ground Connections
As all electrical circuits are a circle, all B- 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 inexplicable component failure. As with the B+ side of the electrical system, the ground side should be checked dynamically using the voltage drop technique.

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

Previous Repairs/Modifications
The vehicle repair history can provide explanations to unusual complaints which seem to elude normal troubleshooting attempts. Incorrect components, unapproved repairs or modifications can have subtle influences on seemingly unrelated systems.