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October 19th, 1999 Article
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I had a vehicle in my shop the other day that reminded me again of how so many people make mistakes with Computer controlled vehicles. This person has been having problems with their vehicle for quite some time and it seems that nobody could find anything wrong with it. The owner himself knows just enough to be DANGEROUS and has tried replacing many components himself but to no avail. This owner knows how to retrieve trouble codes from his On-board system but he has not been able to get any. He has taken his car to other places and they just tell him that everything HAS to be all right BECAUSE IT ISN'T GIVING ANY CODES.

THIS STATEMENT IS VERY WRONG! Just because a system is not showing any trouble codes, does NOT mean that everything MUST be ok. A brief explanation is in order. First, the computer system HAS to be operating BEFORE the system will pick up codes. Most systems are NOT turned on until the vehicle has run long enough to get up to operating temperature. When the vehicle is started cold, (Remember 90 degrees is still COLD to an engine.) the vehicle runs on a preset program in the computer. Just like when you turn on you PC at home, the unit will start and run on its operating system until you command it to run a specific program. During the warm up time, the system will not store trouble codes unless there is what we call a HARD system failure. This means that the system has detected a shorted or open circuit in one of the system it monitors. When the system IS turned on, it has to relate to information that it receives and it has no way of knowing if the information it is getting is correct or not, just as long as it is getting information. This situation is what causes the majority of problems I see with these vehicles. For example; This vehicle here the other day was showing a intake air temperature that I KNEW was not right but because it was reading a temperature that did vary, the SYSTEM COULD NOT KNOW THAT THE INFORMATION IT WAS GETTING WAS NOT CORRECT.

A quick test with a Pyrometer (Hi-Tech Thermometer.) showed the sensor was read less than half of what The temperature actually was. Also, the oxygen sensor was not showing the numbers that I KNEW it should be showing (Because I had a exhaust analyzer in the tailpipe.) But it was reading enough to NOT set a trouble code. So in just a few minutes, I had already found two things wrong and the system THOUGHT it was OK. A computer CANNOT control fuel and ignition PROPERLY unless it is getting PROPER information. But now is where it gets complicated so try and stay with me here. The temperature sensor was telling the computer that the engine was COLDER than it actually was so because a colder engine needs MORE fuel, the computer WAS calling for a RICHER mixture. But because the oxygen sensor was not producing the right information, the computer THOUGHT it was doing the right thing. HOWEVER IN FACT, the vehicle was running WAY TOO LEAN. (Information I would not of had if I had not been testing the exhaust.) There was a problem in the fuel delivery system that would not allow the system to supply the fuel pressure required for proper fuel flow. Three separate problems, all of which were having a very detrimental effect on how the vehicle operated and NOTHING that would set a trouble code in the system.

SO, IF YOU ARE HAVING A PROBLEM WITH YOUR VEHICLE AND YOU ARE BEING TOLD THAT THERE CAN'T BE ANYTHING WRONG, BECAUSE THERE ARE NO CODES, FIND ANOTHER MECHANIC. (With PROPER knowledge and testing equipment.)

"TOOT" Rick "The Wrench" - October 19, 1999
Copyright of Rick The Wrench, 1999

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