Analyzing electrical system issues

Testing a vehicle’s battery, starting and charging system can reveal small problems before they become more serious. Nowadays, the handheld, battery conductance and electrical system analyzer is becoming the most common choice for running these tests...

A remote display digital multimeter might just be the ticket for you in these situations. This type of meter lets you connect the meter to a suspect circuit and then remove the display from the meter body so you can monitor it remotely. You can move the display up to 33 feet away from where the meter’s connected. This feature can come in handy when checking circuits like brake lights, backup lights, and more.

By checking the TPS output voltage with a digital multimeter, you can flag a faulty sensor and cure a drivability complaint. With the ignition switch off, set your meter to the DC volts position and connect the black test lead to a good ground. (If you have an auto-ranging meter, you may want to set it to a manual range so that an automatic range shift doesn’t overshadow a sensor glitch.) Connect the red lead to the TPS signal return wire. Turn the ignition switch on and open the throttle slowly while observing the meter’s display. Voltage should change smoothly as you sweep the throttle from idle to wide-open. A meter with a bar graph on the display can help catch a faulty sensor. If voltage changed erratically, replace the TPS. If the TPS voltage setting doesn’t match the manufacturer’s specs, adjust the TPS first, if possible. If the voltage reading still fails to meet specs after adjustment replace the TPS.

First, always confirm the complaint. Never attempt to diagnose a problem without first confirming that the problem actually exists. If you can’t duplicate it, you can’t fix it. Next, understand the circuit. A few minutes spent understanding circuit operation can save hours of troubleshooting time. Know what, how and why the circuit operates first. Then, test the circuit. Use the equipment and procedures recommended by the vehicle manufacturer and never skip steps. Proper troubleshooting takes discipline, but saves time. After your diagnosis is complete, make the repair. Once you’ve concluded what the circuit fault is, fix it the right way. If the repairs require splicing or disassembly of connectors, follow the manufacturer’s procedures to achieve a reliable, long-lasting repair. Finally, check your work. After repairs have been completed, make sure you try the circuit in all modes of operation. It’s one thing to fix a headlight circuit that doesn’t work, but if there are no high-beams, you’re not finished.

Often, a battery’s open circuit (unloaded) voltage is used solely as an indicator of battery health. This approach is a misdiagnosis in the making. First, look for the load test spec on the battery’s label or in a shop manual. If neither of these is available, use half the battery’s cold cranking amperage (CCA) or three times its amp-hour rating. Using a tester with a load device such as a carbon pile, connect the tester’s load leads to their respective battery terminals and connect the tester’s inductive amp pickup around one of the battery cables (It doesn’t matter which cable). Zero the amps display or needle and set the volts switch to the proper position. Dial in the load with the load control to the specified value and hold it for 15 seconds. The voltage should stay above 9.6 with the battery temperature at 70 degrees F and above. Lower temperatures will show lower voltages. If the battery flunks this test, replace it.


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