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and Instructions > Page 21
Alarm/Immobilizer Control Unit: Diagnostic Aids
Five-Step Troubleshooting
Five-Step Troubleshooting
1. Verify The Complaint
Turn on all the components in the problem circuit to check the accuracy of the customer complaint. Note the symptoms. Do not begin disassemblyor testing until you have narrowed down the problem area.
2. Analyze The Schematic
Look up the schematic for the problem circuit. Determine how the circuit is supposed to work by tracing the current paths from the power sourcethrough the circuit components to ground. Also, trace circuits that share wiring with the problem circuit. The names of circuits that share the samefuse, ground, or switch, and so on, are referred to in each circuit schematic. Try to operate any shared circuits you didn't check in step 1. If theshared circuits work, the shared wiring is OK, and the cause must be in the wiring used only by the problem circuit. If several circuits fail at thesame time, the fuse or ground is a likely cause.
Based on the symptoms and your understanding of the circuit's operation, identify one or more possible causes.
3. Isolate The Problem By Testing The Circuit
Make circuit tests to check the diagnosis you made in step 2. Keep in mind that a logical, simple procedure is the key to efficient troubleshooting.Test for the most likely cause of failure first. Try to make tests at points that are easily accessible.
4. Fix The Problem
Once the specific problem is identified, make the repair. Be sure to use proper tools and safe procedures.
5. Make Sure The Circuit Works
Turn on all components in the repaired circuit in all modes to make sure you've fixed the entire problem. If the problem was a blown fuse, be sureto test all of the circuits on that fuse. Make sure no new problems turn up and the original problem does not recur.
Test Equipment
Test Equipment
CAUTION: 10-megaohm
Most circuits include solid-state devices. Test the voltages in these circuits only with a or higher impedance digitalmultimeter. Never use a test light or analog meter on circuits that contain solid-state devices. Damage to the devices may result.
Test Light and DVOM
12 volt
On circuits without solid-state devices, use a test light to check for voltage. A test light is made up of a bulb with a pair of leads attached. Aftergrounding one lead, touch the other lead to various points along the circuit where voltage should be present. The bulb will go on if there is voltage at thepoint being tested. If you need to know how much voltage is present, use a digital volt/ohmmeter (DVOM).