Basic circuit testing tools such as a tachometer, a test light, and a by-pass jumper allow further circuit examination.
JUMPER WIRES
Jumper wires (figure 6-6) are simple, effective testing aids. They are used to complete a circuit by allowing current to “jump” across a suspected open or break. Thus, they are actually a test of continuity.
When a jumper wire is used, it replaces a suspected faulty portion of a circuit with a know conductor. If the circuit works properly when the jumper wire is in place, but not without it, an “open” is indicated in the area jumped. Use a jumper wire to bypass only nonresistive parts of a circuit, such as switches, connectors, and sections of wiring.
TEST LIGHTS
Test lights are used to check for voltage and continuity.
There are two types: self-powered and non self-powered (figure 6-7).
Self-Powered Test Light
The self-powered test light check for continuity. It consists of a light bulb, battery, and two leads (figure 6-8). If the leads are touched together, the bulb will light.
A self-powered test light is used only on an nonpowered circuit. Select two specific points along the circuit through which there should be continuity. Connect one lead of the test light to each point. If there is continuity, the test light circuit will be completed and the bulb will light.
Non Self-Powered Test Light
A non self-powered test light is used to check for voltage (figure 6-9). The tool is made of a 12-volt light but with a pair of leads attached. After grounding one lead, touch the other lead to various points along the circuit where voltage should be present. When the bulb goes ON, there is voltage at the point being present.
“Scan” Tools
Diagnostic “Scan” tools are the most versatile and effec tive way to isolate circuit faults, identify improper compo nent operation, and otherwise troubleshoot the electrical circuits of the engine management system.
Two “Scan” tools are available to General Motors techni cians (figure 6-10): the hand-held Tech 1 and the T100 Computerized Automotive Maintenance System (CAMS).
Both systems offer Diagnostic Trouble Code (DTC) capa bilities. The Tech 1, however, is more versatile. It can be used inside the vehicle and on road-tests for capturing intermittents.
Tech 1 usage is covered in detail later in this section.