Diagnostic Test Procedures

A diagnostic test procedure is a systematic method of checking the function of a vehicle control system to determine if it is functioning as designed. A diagnostic test procedure is also a systematic method of determining where the problem is when a system is not functioning as designed.


GUIDELINES WHEN PERFORMING TEST PROCEDURES

1. Each category is made up of many tests. Always start at test one of the category. Starting at any other test may give incorrect results.
2. Each test may have many steps and branches. Accurately answer each branch question and perform only those steps required by that answer.
3. At the end of each test (or when specifically directed) reconnect all wires and hoses.
4. The vehicle being tested must have a fully charged battery.
5. visually inspect connectors and wiring of circuit being worked on.
6. After each repair, perform the recommended verification procedure.
7. When checking voltage or continuity at the Engine Controller 60-way connector, use the terminal side (not wire side) of the connector. Probing a wire through the insulation will damage the wire and eventually cause it to fail due to corrosion.
8. Under no circumstances should a test lamp be used in place of a voltmeter.
9. Use care when making electrical tests to prevent accidental shorting of terminals. Such mistakes can damage fuses and components such as the Engine Controller. Also, a second fault message could be set, making diagnosis of the original problem more difficult.