Basic Electrical Troubleshooting

[fdavie]

I've gotten tired of seeing so many electrical problem threads where the poster hasn't really tried any troubleshooting. I wanted to write up a quick howto to describe what to do. What you'll need: A multimeter - There's no reason not to have one. Pick up a cheap one at Autozone for 20 bucks; even the cheap ones are good enough to do troubleshooting. A wiring diagram - Not strictly necessary but amazingly useful for figuring out which wire is which. Useful things: A test lamp - Multimeters can be used to check continuity too, but the test lamp make it easier. The factory test procedure - If someone's already figured out how to troubleshoot something, why pave your own path? How to do it: The basic guideline in troubleshooting is to isolate the fault to a specific component. Do this by breaking the system into testable parts, then testing each part in isolation. This will solve all but the most insidious electrical problems. Let's suppose that your coolant temperature gauge isn't working. First, figure out what components you can break the problem down into. I come up with 4 basic units: the power wiring to the gauge; the sending unit; the gauge; and the wiring between the sender and the gauge. Any other system can be broken down the same way. If you're getting an Oxygen Sensor CEL, you'd want to check the sensor, the wiring, and possibly the ECU. For a window that doesn't work: power wiring, door switches, wiring between switch and motor, and motor. Each system can usually be tested without much trouble. Power supply wiring is simple to test: make sure there's voltage on wiring that's supposed to have power. Anything between 11 and 13 volts is acceptable on a power wire. If there's no power, check a fuse, relay, etc. Testing components Fuses: Check with a multimeter; it can sometimes be hard to tell visually if a fuse has blown. The resistance should be very low; less than .5 ohms. Relays: Check that the relay does not conduct when its off and that it does when it's on. Wiring: Check for continuity from one end to the other; for shorts to ground, or to power. Motors: Check resistance. It should be in a reasonable range; if its close to zero there's probably a short in the windings, if it's very high there may be an open. Try applying power directly to the motor to make sure it operates. Lamps: Check resistance. It should be low. You can also apply power directly to the lamp to make sure it lights. Gauges: Gauges are a little more complex, since there's several kinds used by Honda. If you suspect a gauge, check if there's a procedure in the manual for testing it. Otherwise it might be easier to swap a known-good gauge into the system to see if that fixes the problem. Sensors: Like gauges, each sensor is different. You can check things like oil pressure senders and throttle position sensors pretty easily with a multimeter, but you need more sophisticated equipment to check Hall effect sensors (crank position, ABS wheel sensors) or oxygen sensors. Again, use a factory manual procedure if it exists and you have the tools, or swap in a known good sensor. Generally check the sensor after you've ruled out everything else, as they tend to be more expensive. ECU: ECUs rarely fail, unless you did something like connecting the battery backwards or jump starting with the wrong voltage. Like sensors, check everything else before blaming the ECU for what's wrong. Then, if you suspect the ECU, swap in a known-good ECU. There's many more useful procedures when doing electrical troubleshooting, but these should be enough to get you to the point where somebody can help you.

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[tech8]

Should be sticky.

[ke98248]

Originally Posted by tech8

Should be sticky.

Hopefully it's added to FAQ section.

[Syndacate]

Originally Posted by ke98248

Hopefully it's added to FAQ section.

I added it to the FAQ section.

[MatterMatt]

Yeah, that's all fine and dandy. However, I bet a large percentage of the people here don't have a clue as to how to operate a DMM, or read an electrical schematic. I hate to come across as a prick, but I have little faith in many H-T members' reading comprehension and critical thinking skills.

Perhaps it would be good to start the DMM troubleshooting thread right away. See how many people blow up their meters, or start asking, "why is there a negative sign in front of the reading?", or "what does O.L. mean?"