Tip & How-To about Chevrolet Cobalt

What Else Could Be Wrong?

What Else Could Be Wrong?

I read this question online all the time. People come into my shop regularly with this question on their lips. It usually goes something like this: "I've already replaced the battery and the starter and the alternator...my car still will not turn over...what else could be wrong?" or "The scanner down at [INSERT PARTS SUPPLIER HERE] said 'oxygen sensor'. I've replaced all 4 of the oxygen sensors and the code keeps coming back...What else could be wrong?" This phrase is almost always emanating from a case of gross misdiagnosis.

What is really frustrating for me as a professional technician is that now the customer is broke from all the "guessing". The money for diagnostics that the customer was desperately trying to save has been spent on things the car did not need. Of course, now the customer expects ME to tell them for FREE what is wrong with their car because they have no money left! They just got finished spending $300 trying to save $50! Okay, enough of that subject, we'll move on....

I would say that more than half of the time that I run into this scenario, the problem is being caused by something really simple. Starters that won't crank have a very basic problem with a corroded or loose battery cable; lean oxygen sensor codes are being caused by a hole in a PCV hose, etc. Easy solutions for easy problems...or so it would seem...Here's the catch:

In order to understand what is causing the problem with the system, you must first understand the system that you are trying to fix. For instance, if you are trying to diagnose your starter system, you should know how the system works and how to check for the correct voltage at the proper places within the system. You need to know how to measure amperage so you can tell if you have the correct starter draw. You also need to understand about voltage drops - to keep from replacing a starter when all that is needed is a battery cable end. Most of the people out there replacing oxygen sensors have no clue what an oxygen sensor does or why the car needs it to run correctly. That is why they cannot fathom how a hole in a PCV hose could possibly be the cause of an oxygen sensor code. After all - they are at opposite ends of the engine! (If you have no idea what I just said, I am talking about YOU!)

Then, you have to understand how fault codes work. The general belief of the American Public is that all an automotive technician does is plug-in the "Magic Box" and then replace all the parts that the computer tells him to replace!
This complete lack of understanding is exactly why the average Joe do-it-yourselfer gets stuck paying $500 for replacing all four of the oxygen sensors on his Ford truck when it could have been fixed with a $17 PCV hose assembly! (I have actually seen this happen several times!) Unfortunately, there are a lot of people out there calling themselves "professional mechanics" that also do not understand this.

Fault codes only tell you which of the many systems that are monitored by the computer is malfunctioning or operating outside of its designed "range". It is the job of the person diagnosing the problem to find out WHY the system is malfunctioning. If you do not know how it is supposed to work, it is absolutely impossible to correctly determine why it is not working properly. The counter-persons at the parts store are not professional automotive service technicians. Yes, they sell a lot of parts based on whatever codes they pull out of a customer's onboard engine computer with their generic code reader. That is what they get paid to do...sell parts! An automotive service technician gets paid to understand how your vehicle systems work and diagnose the problem when the system is malfunctioning. In some cases, the fault code can be fixed without any parts replacement at all. Fault codes NEVER tell you what parts to replace.

So here are my professional recommendations:

1. Ask the question "What else could be wrong?" BEFORE spending any money on parts.

2. Take some time to research the problem and have at least a basic understanding of the system you are trying to fix. Don't just ask what parts to replace. Get an understanding of why the person is recommending the replacement of that part. i.e. What does that part have to do with the system? How is it causing the malfunction and/or symptoms that you are experiencing? If you have a fault code, take the time to understand what causes the code to set...not just the generic description of the code, or what parts are involved.

3. If you want the best price for the part, or you want to make sure it is the correct part and will properly fit your vehicle, ask a professional parts counter-person.

4. If you want to know what is causing the problem with your car, ask a professional automotive service technician.

5. Do not confuse #3 and #4 above....this can be VERY COSTLY.

If you would not run straight out to get brain surgery because a nurse thought you might need it, or even worse, perform the surgery on yourself, why on earth, would you do this with your wheels?

-DTTECH

ASE Certified Master Automobile Technician

Also see these other articles by dttech:

My Car Won't Turn Over

Where's The Fuse?

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1 Answer

Rejected Inspection


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Inspect for low coolant level or an incorrect coolant mixture Check the operation of the thermostat (it may be stuck open) ECT sensor signal circuit has high resistance ECT sensor has failed

Oct 13, 2009 | Cars & Trucks

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