Jeff's DIY

Advice on doing your own diagnosis and repair

Advice from the book Can I Do It Myself?

Home Electrical

Home Plumbing. 32

Diagnosis and Repair. 40

Appliance Repair. 44

Home HVAC Repair. 47

Electronics Repair

Gasoline Engine Basics

Basic DIY Auto Maintenance. 61

Automotive Electrical 105

Automotive Relays 105

Horn Issues 105

Check Engine Light 105

Dead Battery Troubleshooting 105

Stereo Says Protect 105

Engine Starting. 63

Engine Doesn't Crank 105

Engine Operation. 72

How to Fix Poor Idle, High Idle, Stalling On Fuel Injected Gas Engines 105

Causes of Gasoline Engine Misfires 105

Checking Gasoline Engine Ignition Systems 105

Firing Order Help 105

Engine Starts but then Dies Within a Few Seconds 105

Engine Revs on its Own 105

Engine Overheats--Where's My Thermostat? 105

Brakes. 87

Auto Heating and Air Conditioning. 96

Lights. 115

Body/Chassis. 120

Real-time and Emergency Auto Diagnostics

Diagnosis and Repair

Step one in repair is to check the product warranty to see if the failure is covered. If the answer is yes, how much of the repair is covered? If it is only parts and not labor, it may still be cheaper to DIY. See if you can diagnose the fault sufficiently to cost the parts. If the fault is easy to diagnose and the parts are inexpensive, I will often do the repair myself rather than hassle with the manufacturer. I do not advise this approach for the average person, however, especially if a DIY repair would void the warranty. Even if you decide to exercise the warranty, it may still be helpful to do a little diagnosis work to make sure the repair proposed by the manufacturer is going to resolve the problem. If you can provide a diagnosis yourself, the repairman may do a better job for you or at least recognize that he/she cannot fool you. Of course, if the manufacturer proposes to replace the product with new and at no cost to you, this is a no-brainer, provided they do so in a timely manner.

Assuming you have decided to DIY, diagnosis comes first when doing repairs. If you are repairing a product that was damaged, the diagnosis may be fairly simple; but, if the product can be dangerous, be careful to fully inspect for damage that is harder to detect. For example, collision damage of a car may include a bent or cracked frame that is difficult to spot. If you have access to good troubleshooting procedures for your product, you may have success in following those to determine which LRU is to blame. Personally, I have seldom found such guides to be useful; but these are in fact the types of documents that professionals use and train from. That is not to say that I wouldn't use one if I had one and could not otherwise diagnose the problem. It's just that I seldom have this type of resource at my fingertips; and, even when I do, I can often diagnose the problem quicker from understanding basic principles. What is of much greater value to me in troubleshooting are designs and wiring diagrams that indicate how the product operates. Knowing these things makes the job of isolating the problem much quicker. When lacking this information, I usually have to fiddle around until I figure out how the product works before I can diagnose the problem.

If at all possible, you should verify that replacement of the suspect part will, in fact, restore the product to serviceability. I can't tell you how many times I have replaced a part that I knew was bad only to find that there were other problems I had not yet uncovered. This happens when the failure of a part that is not obvious leads to the failure of another part that has obviously failed. Given the option, I would always substitute any spare parts I have on hand to see if that will fix the problem, being careful however if I suspect some other problem with the product had caused the bad part to fail (I don't want to ruin another part just because I am too lazy to check for multiple failures). One way to help avoid such difficulties is to always ask oneself how the part failed. If, for example, it appears the part failed due to overvoltage; then the power source is more likely the original problem. Another common cause of overvoltage is a short, which is most often caused by chafing or melting insulation or perhaps the presence of conductive debris. In any case, if the part seems to have failed due to the failure of something else or you cannot understand how the part failed, then continue to trace the failure to the original cause.

With a diagnosis in hand, one must next estimate repair costs. Once you have done your best to identify all of the damaged parts, look up the cost to replace or repair them. Be sure to factor in the risk that you have not found all of the bad parts and also the cost of any tools or bench stock you will need to complete the job. Also factor in your familiarity with the repair steps and the risk of further damaging the product during the repair. Some repairs can be so difficult that they just aren't worth the time. Finally, consider the remaining life of the product and the likelihood of future failures whose repair cost may exceed the value of the item when added to the current repair costs. Many people replace their cars every five years to avoid rising repair costs. The bar is much higher for the DIYer, but the bar still has its limits. For any significant repair, always ask yourself the question "Is It Cheaper to Repair or Buy New?"


See some of my past projects
See my profile on

See my book on Can I Do It Myself?

Another book of mine you may be interested in: BYTE YOUR SMALL BUSINESS