Body Electrical System Troubleshooting - General Information

A typical electrical circuit may include an electrical component, various switches, relays, electric motors, fuses, fusible links or circuit breakers related to the component, as well as the wiring and electrical connectors that connect the component to the battery and to body ground.

To help locate faults in electrical circuits, wiring diagrams are included at the end of this manual.

Before beginning any troubleshooting of a circuit, carefully study the applicable wiring diagram so that you clearly understand the function of the circuit. Narrowing down the fault is usually done by gradually identifying and eliminating normally functioning components in the same circuit. If several components or circuits fail at the same time, the most likely cause is a blown fuse or a faulty ground connection (different circuits in many cases share the same fuse or ground terminal).

Electrical failures are often caused by simple problems such as corroded terminals, a blown fuse, a burned fusible link, or a faulty relay. Visually inspect the condition of all fuses, wiring and electrical connectors in the circuit before performing more specific checks of the circuit components.

When using diagnostic equipment to locate a fault, use the wiring diagrams to plan where and in what sequence to connect the equipment in the circuit in order to locate the fault most efficiently.

The main diagnostic tools include a circuit tester or voltmeter (a 12 V test lamp with a set of jumper wires may also be used), a continuity tester (probe) consisting of a light bulb, its own power source and a set of jumper wires. In addition, always keep in the vehicle a set of jumper cables for starting the engine from an auxiliary power source, equipped with alligator clips and, preferably, a circuit breaker, which can be used to bypass and connect various electrical components during circuit diagnosis. As mentioned above, before testing a circuit with diagnostic equipment, determine the connection points from the wiring diagrams.

Voltage Check

Voltage checks are performed when a circuit does not function properly.

INSPECTION

1. Connect one lead of the circuit tester to either the negative battery terminal or a known good body ground.
2. Connect the other lead of the circuit tester to the terminal of the circuit's electrical connector, preferably the one closest to the battery or fuse.
3. If the test lamp on the circuit tester illuminates, voltage is present in this section of the circuit, which confirms that the circuit between this terminal and the battery is good.
4. Continue in the same manner to check the remaining part of the circuit.

If no voltage is detected, there is a fault between this point in the circuit and the last point tested where voltage was present. In most cases, the cause of the failure is loose electrical connections or poor contact quality.

* Note that power to some vehicle electrical circuits is supplied only when the ignition switch is in the "ACC" (Accessory) or "RUN" position.

Short Circuit Check

One method of locating a short circuit is to remove the fuse and connect a test lamp or voltmeter in its place. There should be no voltage in the circuit.

Move the wiring harness while watching the test lamp. If the lamp flickers, there is a short to ground somewhere in this harness, possibly caused by chafed wire insulation.

A similar check can be performed for each component in the circuit, including switches.

Ground Circuit Check

This check is performed to determine whether a component has a good ground connection.

INSPECTION

1. Disconnect the battery and connect one lead of the self-powered test lamp to a known good ground point.
2. Connect the other lead of the lamp to the harness or terminal being checked.

If the lamp illuminates, the ground connection is good (and vice versa).

Continuity Check

This check is performed to detect open circuits.

INSPECTION

1. After disconnecting the circuit power, check the circuit with a test lamp powered by its own battery.
2. Connect the test leads to both ends of the circuit (or to the "power" end (+) and a known good body ground). If the test lamp illuminates, there is no open in the circuit.
3. If the lamp does not illuminate, the circuit has no continuity.
4. In the same way, the switch can be checked by connecting the test probe to its terminals.

When the switch is moved to the "ON" position, the test lamp should illuminate.

Locating an Open Circuit

When diagnosing a suspected open circuit, it is quite difficult to visually find the cause of the fault, since access to the terminals for checking corrosion or poor contact quality is limited (the terminals are usually hidden inside the connector housing). Sharply tugging the sensor connector housing or its wiring harness in many cases restores continuity. Keep this in mind when trying to locate the cause of a suspected open circuit. Intermittent faults may be caused by oxidized terminals or poor contact quality.

Diagnosing electrical circuit faults is not a difficult task, provided you clearly understand that current flows to all electrical loads (lamp, electric motor, etc.) from the battery through wires, switches, relays, fuses and fusible links, and then returns to the battery through the vehicle body ground. Any problem with electrical equipment failure can only be caused by an interruption of current supply from the battery to the load or by a failure of its return path to the battery.