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Basics of Troubleshooting


Learn what you need to have to have and how to diagnose a problem quickly and efficiently.
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Do the same thing for electrical problems. Check the fuses and fusible links first. Check connections to see that they are clean and tight. Check light bulbs to see if they are just burnt out and the correct type. I had a customer bring a car in and said every time he stepped on the brake his dash lights came on. What he did was put the wrong type of bulb in his brake light and it would feed back into the dash. A dishonest mechanic would have had a field day with this one. He would replace the bulb and charge 5 hours labor locating and repairing a short.

In short, check all the stupid things first. Don't take anything for granted. Car won't start? Check the gas gauge first. That one burned me a couple of times.

When you look for an electrical problem look at it from all angles. Literally look at it forward and backwards. Will it be easier to trace from the component to the fuse box or vice versa? If you are tracing a wire, is the connector buried in the dash? Look at the wiring diagram and find another location to make the same test in a more accessible location. You'll get the same results in a much shorter time.

Lastly check the computer for Diagnostic Trouble Codes (DTC's). For this you will need a scanner or a service manual that explains how to pull the DTC's up manually. If you get a bad injector circuit code, don't assume it's a bad injector. That code is telling you it's in the injector circuit and that includes the wiring, injectors, dropping resistors (on older EFI cars) and computer. Any one of which will throw that code. Get your wiring diagram out and check the whole circuit. To many parts get replaced because "the computer said it was the fuel pump." Don't get burned buying an expensive part only to have it not fix your problem.

When you have found the problem and completed making the repair, check it again. Make sure it is fixed. Sometimes one fault will cause another one that you couldn't see at first. For example, there is a shorted wire between the injector and the computer. You fix the wire and take it for a ride and it still misses. Well you didn't see that the shorted wire burned out the injector. When you test the circuit again, you will see that the injector needs to be replaced also. Double-check your diagnosis; double-check your work and double- check the repair.

Troubleshooting a problem can be tough, even in the best of circumstances, but by following some simple rules, using the right test equipment properly and some common sense, you will locate and repair most problems with your vehicle yourself.

Spark Plugs Tell A Story
Sample Diagnostic Tree

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Additional Information provided courtesy of
ALLDATAdiy.com and Warranty Direct
© 2000-2007 Vincent T. Ciulla

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