420 Section 4 Computer Control Technology
Depending on the manufacturer, it may be
necessary to turn the ignition switch on or off
during the connection and programming procedure.
Double-check any instructions on ignition switch
position before making any connections or beginning
the programming procedure. The next step is to
determine the type of programming that is needed.
Programming a New Computer
If a new computer is being installed, program
only that computer. In many cases, other on-board
computers can be accessed and programmed using
the data link connector. While most computers have
internal circuitry that protects them from accidental
programming, be careful not to program the wrong
computer. Do not attempt to program a new com-
puter with information from the old computer or a
computer from another vehicle. Any attempt to do
this will set a failed programming sequence code in
the new computer’s memory.
Tech Tip
In some cases, an erasure must be performed
on a new computer before initial programming
can take place.
Reprogramming Computers
Computer reprogramming is often needed to
solve specifi c performance or emission related prob-
lems. The auto manufacturer will put out a bulle-
tin and provide the modifi ed software to fi x vehicle
malfunctions. Before reprogramming a vehicle’s
computer, determine the date that the current pro-
gramming was downloaded or check the program’s
calibration number. If the current program is the
latest version, no further actions are required. If the
latest program has not been downloaded, proceed
with the reprogramming sequence.
Before reprogramming most computers, you must
fi rst erase the existing information. After this step is
complete, select the updated calibration informa-
tion from the programming computer or scan tool
menu. Then download the new information into the
computer. On some systems, the erasure step is not
necessary since the programming computer or scan
tool will erase or overwrite the old information as it
loads the new program into the computer.
Tech Tip
If the computer does not accept the new
program or cannot be programmed, check
all connections fi rst. Ensure that the correct
computer is being reprogrammed with the
proper information and that all procedures are
being followed. If the computer still cannot be
programmed, it may need to be replaced.
Allow suffi cient time for the programming to take
place. Monitor the computer or scan tool to deter-
mine when the programming sequence is complete.
Do not touch any connections until you are sure the
programming sequence is complete. After program-
A B
Figure 25-12. Most dealerships now have a dedicated laptop computer for EEPROM reprogramming. A—The laptop is plugged
into the diagnostic link so it can download new information into the vehicle’s computer. B—Icons buttons on the laptop screen allow
the technician to select the correct software for downloading.