Vehicle Electrical Diagnosis

NOTE: when trouble shooting an electrical system, make sure there are no electrical loads ON, except for the circuits or system being tested. This will help prevent false readings and the chance of a dead battery after the car has been serviced, always visually inspect the battery to be sure the Green Eye is visible in the battery hydrometer.

BEFORE TROUBLE SHOOTING
1. Visually inspect the wires and connectors.
2. Verify that terminal pins are clean and that there are no loose pins or terminals.
3. Verify that the Weather-Pac connectors are in good condition and sealed properly.
4. Check the minifuse, maxifuse or circuit breaker used to protect the circuit or system being tested.
5. Check the battery for damage, state of charge, and for clean and tight connections.
6. Check the accessory drive belt.

FIVE-STEP TROUBLE SHOOTING
1. Verify the complaint.
^ Perform the System Performance Test, if the section has one, outlined at the beginning of each section. Do not fix only part of the problem. Do not begin disassembly or testing until you have narrowed down the possible causes.

2. Consult the Cause-To-Complaint Charts and analyze the electrical schematic for the system being tested.
^ Use the Cause-To-Complaint Chart, to find the possible cause of the problem.
^ Look at the electrical schematic for the problem circuit. Determine how the circuit is supposed to work and look for minifuses, maxifuses, circuit breakers, wires and ground shared with other systems or components. See if a shared wired is at fault by checking the other components fed by the wire.
^ Based on the symptoms and your understanding of the circuit operation, identify one or more possible causes of the problem.

3. Isolate the problem by testing the circuit. Use diagnostic service probes as needed on 18, 20, and 22 gage wires.
^ Perform circuit tests to check the diagnosis made in step two. You can either test for the most likely cause of failure first, or perform the tests which are most easily and quickly done.
^ Generally, fuses and grounds are easiest to check.

4. Fix the problem.
^ Once the problem is identified, make the repair. Make sure to use the proper tools and safe methods mentioned in this service manual.

5. Make sure the circuit works.
^ Turn on all components in the repaired circuit in all modes of operation. Make sure no new problems have come up and that the original problem has been fixed.

HELPFUL HINTS
1. If a fuse is blown, look for a short to ground in the circuits between the junction block and the component or an internal component short.
2. Before checking the integrity of a circuit by means of a voltmeter or ohmmeter, check to see if other components or systems fed or grounded by the circuit are operating properly.
3. Verify that the connector pin terminals are not spread apart, broken, worn, or corroded due to salt water, antifreeze, etc.
4. Verify that the terminals and pins are in their correct cavities.
5. Opens normally occur at connectors, terminals and splices.
6. Use the diagnostic service probe and a multimeter to diagnose circuits that contain 18, 20, or 22 gage wires. The diagnostic service probe causes a minimum of disturbance to the circuit wiring and connections.

Headlamp Schematic - Sneak Circuit:

SNEAK CIRCUITS
Understanding sneak circuits can help in quickly diagnosing electrical problems that can, at first, seem very complicated.

A sneak circuit can be defined as an unplanned complete circuit. This type of failure is different than a short circuit.

A sneak circuit can occur when more than one component is using the same ground path or power feed. Sneak circuits can happen if a common ground is lost, a fuse is blown, or a wire is grounded between components.

The most visible sneak circuit on the Saturn vehicle is the headlamp circuit. The headlamp circuits are fed by two fuses, the left headlamp fuse and the right headlamp fuse. Note that the left headlamp fuse feeds both the high and low beam bulbs on the left side of the vehicle. Likewise, the right headlamp fuse feeds both the high and low beam bulbs on the right side of the vehicle. On the ground side of the headlamp circuit the important thing to notice is that both the left and right low beams bulbs are switched on and off together. Likewise, both the left and right high beam bulbs are switched on and off together.

If the left or right headlamp fuse blows, evidence of the sneak circuit will be the headlamp bulbs on the side of the blown fuse glowing dim yellow. This is caused by the sneak circuit from the good headlamp fuse, through the bulbs, to ground through the headlamp switch.