You usually can spot customers' attitudes as soon as they walk into the shop. Some are cool - others are apprehensive. There are some you wish would never step inside your door because you just know they are going to be hard to please. You learn to read people's attitudes when you deal with the public.

People also have complex personalities, which take a little longer to read. As you spend time with a customer, you get to know a little about their personality. In subsequent visits, you get to know them better and better over the years as facets of their personality begin to come out. You learn some customers have "buttons" you don't dare push. You learn to work with different personalities.

I once had the opportunity to work on a car belonging to Charlie Pride, the famous country and western singer. He had a problem that he was very interested in getting fixed the first time. Tapes in his Mark IV 8-track were running at the wrong speed and he couldn't rehearse while he was driving because it threw his timing off. By the way, for the benefit of you youngsters in the industry, an "8-track" is a cassette sound system that was very popular in the vehicles of the 1970s that preceded the modern mini-cassettes used today. (Am I dating myself, or what?)

He followed his car through the shop, getting his head under the dash with us. I got to know him a little bit just by talking with him for a while. He was so pleased with the repair that he ended up singing us a couple of songs back in the shop and practically halted shop production for a couple of hours singing and signing autographs. I remember how the customers in the waiting room strained to get a glimpse of him. He has a genuinely nice personality and he paid the bill in cash.

The study of human personality has become a profession for psychiatrists and they make a lot of money at it. In the automotive service industry, the study of human personality can be a valuable asset in working with customers. Yet, there is another area in the study of personality that can be of benefit in the automotive service industry. It is the study of vehicle computer personality. I have begun to stress this more and more in my seminars because it can be a very useful tool in diagnosing driveability problems. It may seem strange at first to think that an inanimate object such as a computer can have a personality like humans, but think again.

We have all used what we have called "experience" over the years in vehicles that never had a computer. You just get to know how some vehicles behave when a certain problem occurs. You see a symptom you have seen before and know exactly what to check or change each time you see that symptom on that type of vehicle. You are using your experience with vehicle "personality" to diagnose and repair.

Vehicle computers have very specific personalities created by their programming stored in memory. Figure 1 shows the three basic blocks of a computer: Inputs, The Brain and Outputs. A computer programmer designs a software program to operate a vehicle computer system in the most efficient manner to minimize emissions and improve fuel economy and performance. Software program information is stored in PROM (Programmable Read Only Memory) and ROM (Read Only Memory) and some other fancy sounding names for new style memory devices, such as EEPROM (Electrically Erasable Programmable Read Only Memory). All this produces computer personality that can provide useful troubleshooting information.

All computers of the same part number have the same programming, so they have the same basic personality. The way the computer responds to inputs and how it controls outputs takes a very definite pattern that is consistent with all similar vehicles. Certain problems on these vehicles always seem to make the vehicle behave in a certain way that we come to recognize from experience. That's using vehicle computer personality to fix problems. But, take it a step further.

Once you work on a vehicle and diagnose a problem, you have spent time with the power control module (PCM) programming and have begun to learn about the idiosyncrasies of the PCM's personality. You are getting to know this vehicle's computer personality and how it behaves and handles problems. We need to learn to spot computer personality so we can learn to use it to our advantage.

My first experience with computer personality that began to open my mind to new possibilities using this concept occurred when I began to check 02 sensors with a lab scope to monitor the fuel management system back in 1981. Some thought I was just showing off. Well, I was, but it really did help troubleshooting computer-controlled systems when little information about these systems was available.

I noticed that GM cars in the early 1980s changed often between rich-lean and lean-rich. The 02 sensor voltage toggled nicely on the lab scope display several times a minute. We call it "cross-counts." Since I worked mostly on GM cars at that time, I became used to proper 02 sensor performance as a measurement of the fuel management system's performance. If the 02 voltage roamed too high for too long, I quickly knew the engine was running too rich. If the 02 voltage roamed a little low too long, I knew the engine was too lean. I also began to notice how different GM cars had little subtle differences in the 02 voltage changes. I learned how to recognize proper fuel management operation and what might be wrong if those subtle differences where missing in the waveform. Without realizing it at the time, I was becoming accustomed to GM's electronic control module (ECM) personality and using it to my advantage.

Then one day I checked a Ford 02 sensor waveform on one of the old "Eeek 3" systems. What a difference I found! At first I thought something was wrong until I checked others and found that Fords in those days toggled a lot slower between rich-lean and lean-rich. That's just their "personality." I learned it's OK for a Ford to toggle slower. I began to learn about the difference in personality between manufacturers. Each has their own basic personality and then subtle or obvious differences between platforms of the same manufacturer.

Following are some tips on recognizing important aspects of a vehicle's computer personality. Once you become aware of these, you might better understand how to use a computer's personality to determine what could be wrong.

We have already discussed response to O2 sensor voltage changes. This is one of the most classic indicators of computer personality. Since we all have so much free time on our hands, it would be a good idea to simulate problems and watch the 02 sensor voltage response to the problem you created. You'll see just how unhappy a PCM can get and learn a lot about the PCM's personality.

Another good indicator of computer personality is found in the "rhythm" of the data stream. PCMs (ECMs) of the early 1980s had very short data streams. Recent PCM technology produces a complex data stream. Each has its own rhythm that can be sampled with a digital logic probe with tone. The data stream plays like a bizarre song through the logic probe. You can't dance to it, but you do get to know the "melody" and you can almost tell the difference between good and bad data stream with a little practice. A fellow tech had such a musical ear that he'd rather listen to the logic probe melody than look at the LEDs. He could tell more from the melody than I could using the melody and all the LEDs. I wondered if he was putting me on, but I let it go because he was bigger than me. But, he was almost always right. Go figure.

Personality affects the priority of individual sensors in setting a diagnostic trouble code (DTC). Some PCM personalities get downright upset when a particular sensor is sending incorrect information (out of range). Knowing how individual sensors affect vehicle performance and the PCM helps a lot in diagnosing driveability problems when there are no DTCs to give you the first clue.

Personality affects the time duration to respond to sensor changes. Make a sensor value change, even forcing it out of range, and see what the PCM's personality says about it. You might find the PCM has a particular infatuation for a sensor and you didn't realize they were so in love.

Personality affects the way vehicle actuators respond to sensor input changes. One of my favorites is to pull the 02 sensor wire (I love 02 sensors for diagnostics), lick my thumb and then touch the 02 wire conductor with my wet thumb. Then I touch the battery "+" post with my other thumb to indicate if the system is rich and watch injector pulse width decrease. I then touch the chassis and drive the 02 lean and watch the injector pulse width increase. This gives me a feel for how fast the injector pulse width changes and some insight into PCM personality. I also determine how fast changes occur; after all, it's part of the PCM's personality.

Personality affects the time it takes to set a specific diagnostic trouble code. Code setting conditions can change from one model year to the next. Disconnect a sensor and see what changed in the new model year to learn about how the personality has matured in the next model year. I have seen time duration change dramatically from one model year to the next and you wouldn't want to troubleshoot with the old PCM personality in mind. Computer programmers do grow up, you know.

For fun, why not test a computer's personality by disconnecting a sensor and seeing what happens? You'll quickly learn a lot about a model year's PCM personality. You will be surprised how you can detect personality traits of PCMs simply by spending some time with them and pushing their buttons.

Who knows, maybe they'll sing you a song all the way to the bank.

Vince Fischelli is president of Veejer Enterprises Inc. (www.veejer.com) in Garland, Texas.

RATE THIS ARTICLE What do you think of this article? Your input will help AutoInc. develop additional articles on this subject. Share your thoughts! Your name Your e-mail address

MOST ACCESSED ARTICLES Fuel Injection Service, Not Just Cleaning The Art of Extraction EGR Systems: Operation and Diagnosis Proactive Target Marketing:_Rethinking Your Business Strategy Engine Performance: HO2S Diagnostics MOST E-MAILED ARTICLES Developing Employee Potential How Critical Thinking Can Help Your Business How to Diagnose the Ford Glow Plug What to Look for When Shopping for the Right Shop Management Software Putting a Price Tag on Complaints

AutoInc. Web Site | ASA Web Site | EPA develops New Stormwater Regulations | ANS Service Myths and Facts | Towing and Rental cars - Body Shop Services | Handling Personnel Crises | Guest Editorial | Tech to Tech | Tech Tips | Shop Profile | Net Worth | Stat Corner | Chairman's Message