Do you need a Diagnostic Scan Tool?

You are cruising along the open road. Traffic is light and you are making good time toward your destination. The stereo is blasting your favorite tune and the kids are behaving in the back seat. Then without warning that ugly amber colored warning light comes on: CHECK ENGINE. Or some variation such as Service engine soon.

Is it time to panic? If you have seen this light before you may be familiar with what to do next. If its the first time you have seen this light come on while driving you might become a little worried. The light may or may not accompany a change in engine performance. In other words, the car may continue to run fine as though nothing is wrong. In some cases engine power may be reduced while the light is on. In either case what do you do?

Most all other warning lights in the car such as BRAKE, TEMP, or OIL are red when they illuminate. This of course means to stop the vehicle immediately. The CHECK ENGINE light is amber in color meaning caution. There is no immediate danger to the vehicle however it needs to be serviced as soon as possible. But what exactly does this light mean?

All modern cars use an onboard computer to control engine functions such as fuel delivery and spark. Newer cars have several onboard computers however the one responsible for controlling the engine is known as the Powertrain Control Module, or simply known as the PCM. The PCM receives input signals from various electronic sensors on the engine and the exhaust system. These sensors measure such things as the temperature of the engine, the angle of the throttle (How much you have your foot buried into the gas pedal), the amount of fuel in the exhaust, and the speed of the car. There are as many as 15 or more input sensors on modern cars and all these sensors report their reading to the PCM. In return the PCM uses this information to determine output controls such as how much fuel the engine needs and when to fire the spark plugs. This allows the engine to perform with the best possible performance, fuel economy and lower emissions. In a future blog I plan to cover this a little more in depth.

The PCM has a strategy built into it. In other words the computer compares the signals it receives from all the sensors to the strategy programmed into it. If one or more of the signals sent to the PCM doesn’t jive with the strategy a code is logged for that failure and the check engine light is turned on.

Using a Diagnostic Scan Tool a mechanic is able to connect to the PCM and read what was logged in the form of a Diagnostic Trouble Code (DTC). This code identifies the sensor and circuit that is sending the funky reading that doesn’t match the strategy programmed into the PCM.

Can you as the car owner do the same thing? Most certainly. Diagnostic Scan Tools are available at almost all auto parts stores and have come down in price. A nice hand held scan tool capable of retrieving and clearing DTCs can be found for as little as $50 online and at some parts stores. This is compared to several hundred dollars just a few years ago. Some auto parts stores may even loan you a scan tool or offer to retrieve the DTC for you.

But what information does this provide you? There hundreds of Diagnostic Trouble Codes capable of being stored in most PCMs to cover just about any failure logged into its memory. Some of these are fairly straightforward, others a little more complicated. If you plug a scan tool into your PCM diagnostic connector the code or code you retrieve will only tell you the sensor or circuit responsible for turning on the CHECK ENGINE light. As an example you might retrieve information on the display such as: P0320 Ignition/Distributor Engine Speed Input Circuit. 

Where do you go from there? Once a trouble code is retrieved there is additional diagnostic information to trace down the cause of that failure. Is it a sensor? Is it the wiring to a sensor? Or something else?

There are many publications online as well as in books to help diagnose DTCs retrieved from a Powertrain Control Module. But this is only the beginning. The Diagnostic Scan Tools owned by professional repair shops are capable of retrieving the vast amount of information stored in the PCM to aid in diagnosis. These often show live data while the engine is running as well as the data that was stored when the fault occurred. The scan tools capable of providing this information start at about $2,000. A diagnostic flow chart and a scan tool capable of reading data are a must when diagnosing the cause of a CHECK ENGINE LIGHT.

But should you own a hand held scan tool capable of only retrieving Diagnostic Trouble Codes? In my opinion it is not a high priority as it is only good for information. Your money may be better spent on other tools. However it is handy to have to retrieve the Diagnostic Trouble Code before taking it to the shop. This may help you understand what the repair shop is dealing with. This may also give the shop a “heads up” that you are a car owner with some kind of knowledge of their car. If the Diagnostic Scan Tool has a feature to clear the code and turn off the light, do not and I repeat DO NOT clear the code after you retrieve it. This may also clear any data that was stored when the failure occurred. Doing so will make your mechanic dislike you very much and this may be reflected on your repair bill.


Charge it? (Please don’t!)

For those of us living in the southern California desert, it is impossible to imagine driving a car not equipped with air conditioning. Summer temperatures can easily exceed 110F in this part of the country.

At one time air conditioning was considered an expensive option on cars sold in the US. The early systems were clumsy and often crippled the fuel economy of a standard car because of the added weight of the components along with the power needed to operate the compressor. Newer systems are much lighter and less energy is wasted driving the compressor.

The cost of HVAC (Heating, Ventilation, and Air Conditioning) systems on a modern car can be pretty expensive. Yet most car owners do not have the expensive equipment needed to repair their HVAC systems at home. This is one of the few areas of a car where I discourage anyone unfamiliar with a car to attempt their own repair.

In recent years several automotive parts stores started selling kits to allow car owners to recharge their air conditioning systems at home. I have also seen these same kits sold online as well as large department stores. For about $20 a person can by a can of refrigerant with the tool needed to connect to the low side charging port of the HVAC system. The advertising for these kits show a happy car owner sitting inside their frigid car after recharging the system on their own.

This is one of the worst products I have seen offered to the general public. Not only are they dangerous, the kits offer no fundamental information on how an air conditioning system works. Furthermore, the refrigerant in the kit is often mixed with other chemicals that promise to seal small leaks. Essentially this is introducing a product to the vehicle that was never designed for the car.

A low refrigerant charge will certainly reduce the performance of the HVAC system. If the refrigerant charge is low enough the system will quit working altogether. Yet this isn’t the only thing that will keep an air conditioning system from operating properly. In modern cars there are several electric sensors within the system to help control the compressor’s operation. If one of these sensors fails or receives a negative signal it may shut off the compressor even if the refrigerant charge is sufficient. This is why a professional evaluation of the entire HVAC system is necessary before adding any refrigerant.

Adding refrigerant to a system that is already full can damage the system. Not to mention an overcharged system will also keep the compressor from engaging. Adding refrigerant to a system that is empty can be a waste of money. If the system is empty of refrigerant there is a leak. Recharging the system becomes a waste of money as that recharge will eventually leak out of the system.

Handling refrigerant without the correct equipment can be dangerous. Refrigerant can blind a person if it gets into their eyes. It can also cause freeze burns to the skin almost immediately. The biggest danger however comes when the can is connected to the wrong charging port of the HVAC system. Although this is difficult, it is not impossible. With high side pressures reaching nearly 300psi, a can of refrigerant can burst like a hand grenade.

To correctly charge an HVAC system the refrigerant must me weighed. A professional repair shop will often pull the HVAC system of the car into a vacuum. This will pull any moisture from the system before a charge. Once the vacuum is achieved the mechanic will often make certain the system is able to hold the vacuum. If the system can’t maintain the vacuum, then the system has a leak. Once it is certain the system can hold a vacuum, the mechanic then weighs out the correct amount for the system and begins to charge the system to the correct amount. All of this is performed with a machine that recovers, recycles, and recharges the air conditioning systems on most makes of automobiles. This machine is several thousand dollars and must be inspected and re-calibrated every few years.

While I encourage any owner to take on most repairs they are comfortable with, the HVAC system is one best left to professionals.


Where do you begin with your car

Are you capable of maintaining your own car? Should you leave this to a professional? Do you pay a friend?

This depends on several things. For most people the time off from their job is best spent taking care of the household and children. Or simply relaxing. Some car owners simply don’t have the time to take on an additional chore. The car sits quietly in the garage resting from countless trips to the soccer field or supermarket. Spending time on the car simply does not fit into an already full calendar.

But lets assume for the time being you have the time. You have a couple extra hours a month to spend on your second largest investment. Are you up to it?

When most car owners purchase their hot new ride there is so much excitement that many important things get ignored. Most importantly the owner’s manual. It often sits in the glove compartment going largely ignored until something specific is needed. Like how to set the clock on the stereo. Or how to adjust that driver seat that has four switches on the side. Apart from that the manual goes back to its home in the dark glove box under the multitude of napkins lifted from the nearby fast food restaurant.

If you are considering maintaining your own car, now is the time to pay attention to that owner’s manual. Where is the fuse box located? How often should you rotate the tires? Where is the jack for changing a flat tire? The information is in the owner’s manual waiting for you to discover it.

The next consideration is the  tools necessary to take care of certain tasks. I’m not talking about that crowded all purpose drawer in the kitchen with a hammer and screwdriver sharing space with the small junk that has no other place in the home. A good assortment of hand tools can be purchased from a number of places. I will get into the details of what should be in your tool collection further down.

Before taking on any task involving your car I also recommend purchasing a repair manual. Most parts store carry a variety of paperback repair manuals specific to most vehicles. This is a very good investment that will set you back about $25. This information can also be found on different websites on a pay as you go basis. However I always recommend an actual paper manual to read just about anywhere. Holding a tablet or laptop at the side of a car is not always practical. Not to mention the book can be kept in the trunk should you find yourself on the side of the road in need of information. The books are easy to read and chocked full of pictures and diagrams. Even if you choose not to do your own repairs, you can easily read on what the mechanic suggests.

I also want to address PPE (personal protective equipment) most mechanics have suffered an eye injury or a nice hand wound that could be easily avoided. A pair of safety glasses is a must. Yes they look goofy, but so does an eye patch. Gloves are also recommended if you don’t care to be burned or have a knuckle gash. Bump helmets are also nice to have when working underneath the car. Some of the best swear words Ive learned have come after busting my head on a bolt. Bottom line, get this PPE together and keep it ready to use.

Earlier I mentioned tools. I could spend hours recommending what tools you should on. Most of it depends on how extensive your willing to tear into your own car. But for the sake of this blog I am going to recommend the basic tools you would need for simple maintenance tasks. Most tools can be purchased in a set. Several retailers offer tool sets that come with the most basic hand tools. This is the best investment. The most basic tool set should include: Combination hand wrenches in sizes 8mm to 19mm. Some may also include fractional wrenches from 5/16″ to 3/4″ however most car manufacturers have gone to strictly metric fasteners. A good tool set should also include a ratchet and socket set with the same sizes as the hand wrenches. A set of screw drivers should also be an essential part of your tool set. Both standard and Phillips tips. Some may also include specialty tips such as allen an torx tips.

A good tool set with all these components will probable hit your credit card for about $150. But are well worth the investment.

Finally a good floor jack and jack stands are needed should you choose to work underneath the car. Never and I mean Never ever work underneath a car without it being supported by sturdy jack stands. I can not stress this enough. If you have a jack but no jack stands, don’t even use it.

While you are getting all this together, I will be preparing additional tips to get you started. I look forward to being your pocket mechanic.


What is yourpocketmechanic?

I have been an automobile mechanic for 34 years focusing on the maintenance and repair of cars and trucks. 20 years of my experience comes from working in the retail automotive business. The other 14 years have been spent working with fleet repair for a major utility company.

I am hold an ASE master certificate in auto repair as well as an ASE master certificate in heavy duty truck. These must be renewed every 5 years as I have done since 1984.

The cost of repairing and maintaining a car has grown exponentially in the last 20 years. The average repair for a simple breakdown can cost a thousand dollars or more. Maintaining a car or light truck is no cheap task either. Many car owners are at the mercy of the growing number of “quick service” businesses that lure the person in with a deal to good to be true in hopes of earning more money of recommended repairs.

I would like to help owners take care of their own vehicles with suggested ideas on how to do some of this maintenance on their own as well as offer ideas on reducing the cost of having this work done elsewhere.

I want to answer some of the questions that come to a car owner’s mind. Though I may not be able to answer all questions. I will do my best to appeal to a wide variety of topics.

I am your pocketmechanic.