How a Car Computers Work
What Does it Do?
A car's computer or PCM - ECM (powertrain control module - engine control
module) is designed to read various sensors such as the crankshaft position
sensor to deliver electrical commands to the fuel injectors, ignition system,
transmission and camshaft position to name a few. This is done by using a
predetermined program developed by individual manufactures such as Gm, Ford and
Honda. Each manufacturer has its own developed program which is unique. The
computer will make changes these systems and components by monitoring the engine
while it's running to maintain optimum perform and fuel economy. Hybrid
vehicle's computers have the additional job of coordinating the electric motor
in conjunction with the native gasoline engine. A car can have several other
computers onboard such as the BCM (body control module) and TCM (transmission
control module) and will be connected to one another using a communication data
This computer is a self learning device which has been programmed to adjust for
driving conditions and the habits of the driver. This adaption is learned over
time and will change while in operation. There are several system monitors that
will run in the background of the computers operation system. These monitors
test and re-test certain systems such as the EVAP emission system to make sure
they are functioning correctly. Monitors must cycle completely before the
computer will give the car a clean bill of health. This is why you must drive
the car a certain distance after clearing the codes before a smog or safety
inspection can be performed.
Where is it Located?
The computer is located in one of two places, either under the hood or under the
dash. Each manufacturer will decide to install the computer anywhere makes sense
to them while designing the car so each location will be different. When
locating the computer follow the main engine wiring harness and it will lead you
to the location of the computer.
What Goes Wrong?
A car's computer can go out at anytime due to vibration or an electrical surges
caused by the alternator, battery or starter. Moisture will also take it's toll
on these items. Fortunately your cars computer has been programmed to sense
system malfunctions and is able to record the problem in the form of a trouble
code which will then turn the check engine light on. So the appropriate repairs
can be made a
code reader is then used to access the computer and display the code
these repairs are completed the
will need to be cleared
and erased from the computer memory. If the computer
has determined a large enough problem has occurred it will switch the car over
to "limp mode" which is designed to keep the engine running in a reduced power
mode to prevent engine damage or increased emissions. There are many connections
between the sensors, actuators and various motors in the system. These
connections are performed by a main
harness which must be repaired
when a short or open circuit occurs.
Can I Replace My Cars Computer?
In older cars made before 1996 its possible for you to change the car's computer
because the operation system is pre-programmed by the manufacturer and you
simply unplug the old computer and install the new one and you are off and
running. Car's made after 1996 have more adaptive programs which are updatable.
This means that a particular program must be downloaded from the old computer to
the new one using a scanner capable of doing such an operation. Also any factory
updates should be done at the time of the new computer installation.
How Much Does It Cost To Replace?
There are two ways to go about replacing the car's computer. The first is to go
to the dealer and have them replace the unit while supplying any updated needed
at that time which can cost between $1000.00 (US) and $2500.00 (US) in most
cases depending on the car's manufacturer. The second way is to get a
replacement from a wrecking yard which will work in most cases and will usually
cost between $350.00 (US) and $600.00 (US).
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Article first published 2017-01-27