• Brian Keene

Diagnosis and Troubleshooting Tips for your Car


Remember Occam's Razor - The simplest answer tends to be the right one.


In this blog post we go over some basic diagnostic tips to help solve your car problem. These are general tips that can be applied to any type of vehicle. If you are unsure of the issue with your car, we recommend taking it to a dealership or shop that specializes in that make of car. Although the premium price for labor to diagnose and repair may seem high, many times it's still cheaper than purchasing a number of parts that don't solve the problem. Please take a look at our dealer list since they are experts in all things Subaru and will utilize us if they see it necessary from an electrical perspective.


The most important tip we can give for doing diagnosis is to eliminate variables. It’s tempting to just buy a replacement part but when you install it and the problem doesn’t go away, you’ve now added a variable instead of taking one away (not to mention the expense of doing so). We suggest doing one change at a time, test it, and measure the results. Then test and repeat, test and repeat. In our experience most issues with a car are something small and simple. Work through the issue but don’t immediately replace a large piece of the car.


The best place to start for diagnosis is determining if there are any codes. Most car parts stores will let you borrow one for free! Get a code reader and type any codes into your favorite search engine. Although forums don't get a ton of traffic these days they are an incredible resource for diagnostics with the archived information. There are a lot of online forums and Facebook groups that may have a solution to your issue already figured out for you. Be wary of online “experts” and make sure you’re following the advice of someone who is familiar with your make of car.


Sometimes an issue may present a symptom that is not related to the damaged part. Once you have checked if there are codes or not, the next step is to figure out if the problem is mechanical or electrical. Two common scenarios are a misfire which tends to not be an electrical issue but presents itself that way and no crank position input (no start) due to a broken tooth not a bad sensor. Go to the source of the issue and inspect it to see if it’s electrical or mechanical. This will immediately eliminate a lot of variables to continue trouble shooting.


Not all tools and parts are created equal. If you are going to make a DIY repair, make sure you utilize the proper tools and OEM parts for the job. One example we see a lot is replacing the front 02 sensor with an aftermarket version because they OEM 02 sensor is quite expensive. However, this sensor is very electrical interference and the ECU sees anything out of the ordinary it will not work properly.


If the issue is mechanical: The above logic still applies here, but since we’re not mechanical experts we don't have as many detailed experiences in common issues like we do for the electrical side. If you can find a shop that is an expert in your type of car, that is even better! Don’t go to a Domestic car shop for your Japanese Subaru. Some common issues to check are spark plugs, fuel filter, compression, ignition coils, injectors, fluids, and/or bolt tightness. Remember the simplest answer tends to be the right one.


If the issue is electrical: Since we are electrical experts we put some common troubleshooting tips below. Every car is different and every project is unique. The key here is patience and don't pull more apart than you have to. See above about adding variables.


1. Check your grounds. The most common wiring issue we’ve encountered is bad grounds leading to electrical gremlins in the system. Check out this blog post to learn more about the grounding system – https://www.iwireservices.com/post/grounding-issues-iwire-grounding-kit

2. Get a multimeter and the wiring diagram for your car (these are available online for free in search engines, online forums, or social media groups). Start checking the connections to make sure it’s getting the proper inputs it needs like power, signal and ground.

3. Electrical problems tend to be at the connection point of a harness, not in the middle of it. The 2 places where we see issues not at connection points are places where the harness gets hot like the downpipe and the fender wells where the tires can bite into the harness.

4. Wiggle test. Shake the harness or wiggle the connector and see if that changes the issue. Sometimes a problem can be a terminal that is not fully seated inside the connector or the connector is damaged or corroded. You can buy replacement connectors on our website if you decide it’s a connector problem. Many times during an engine build the main connectors can get dirty while off the car so using an electrical contact spray can help clean them out. Just make sure you remove the gaskets before since the spray will cause the gaskets to swell.


Repair vs Upgrade:

It can be tempting while you’re sorting out a problem to replace the part with an aftermarket part. However, until you know the source of the actual problem do not put in a new part, especially an upgraded part. One example we see a lot is the car is acting funny and the thought to solve it is to put in a stand alone ECU. Until the source of the problem is found, you do not want to change out any major pieces. By throwing parts at the car, you are adding more variables which makes diagnosis even more difficult. If a new part you’re testing doesn’t fix the issue, take it off the car and put back the original part.

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