Chapter 24 Sensor, Actuator, Computer Service 479
Note: 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
correct 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 determine when the
programming sequence is complete. Do not touch any con-
nections until you are sure that the programming sequence is
complete. After programming is completed, turn the ignition
switch to the position called for and disconnect the computer
or scan tool. Then, use a scan tool to check the computer and
control system operation. While doing this, make sure that
you have installed the proper program into the computer by
checking the program calibration number.
Replacing Removable PROM
Most computers use the old PROM (memory chip) dur-
ing computer replacement. The PROM seldom fails and stores
data for the specifi c make and model car. You must commonly
remove the old PROM and install it in the new computer.
Illustrated in Figure 24-33, remove the cover over the
PROM. Then, use a PROM tool to grasp and pull the PROM
out of its socket. Avoid touching the PROM with your
fi ngers because the body oils on your hand could affect
PROM operation.
Before installing the old PROM in the new computer,
check that the PROM pins (terminals) are straight. Bend
them straight if needed. Also, check the reference mark on
the PROM. A PROM usually has an indentation or other
marking to show how to reinstall the unit. Make sure that
the PROM has the correct part number for the car.
To install the PROM, place the PROM pins into the
socket with the reference mark correctly positioned. Then,
use a blunt tool, like a wooden dowel, to press the PROM
down into the computer. Press on each corner to make sure
the PROM pins are fully seated in their sockets.
Some PROMs use a carrier, which is a plastic part that
surrounds the outside of the integrated circuit chip. If used,
you must use a blunt tool to push the PROM so that its top
is fl ush with the top of the carrier. This will ready the PROM
for installation into the computer. Install the carrier and
PROM in the computer with the reference mark pointing
properly. First press down on the carrier only. Then, press
down on the center of the PROM with a blunt tool. Press on
the corners until the PROM is fully seated in the ECU.
Install the PROM access cover and then install the com-
puter into its mounts. Connect the connectors to the computer.
Reconnect the car battery, turn on the ignition, and activate
self-diagnostics. Make sure no trouble codes are set as a check
of the computer and PROM. A code might be set if the PROM
is not fully seated or a pin is bent over, for example.
Figure 24-33. Most main computers have a removable PROM
or memory-type integrated circuit. This chip is calibrated for the
exact car. It must usually be removed and reused in the new
computer. A—Remove the PROM’s access cover. Screws nor-
mally hold the cover in place. B—Use a PROM tool to grasp
and pull the carrier and chip out of its socket. Avoid touching the
PROM with your hands. C—PROM is frequently enclosed in a
carrier. Carrier protects the PROM pins during replacement.
A
B
C
Computer
Prom
Access
Cover
Lift Out
Carefully
Carrier
and Prom
Prom Tool
Reference
Mark
Prom
Prom Carrier
Prom
Pins
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