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.)
