Chapter 25 Computer System Service 419
Updated PROMS
An updated PROM is a modifi ed integrated cir-
cuit produced by the auto manufacturers to correct
a driveability problem or improve a vehicle’s perfor-
mance. The old PROM is simply removed from the
computer and replaced with the updated PROM.
Updated PROMs are produced to correct prob-
lems like surging, extended cranking periods, exces-
sive emissions, cold and hot start problem, and
unusual driveability problems that cannot be iso-
lated to one system. If you are faced with a problem
and cannot fi nd the cause, check with the local deal-
ership to fi nd out if there are any updated PROMs
for the vehicle that address the problem.
CAUTION
Installing a performance chip
(aftermarket PROM chip that enhances
engine performance) or a nonstock
ECU will void the vehicle’s warranty and may be
a violation of federal law. Before installing any
nonstock performance part, make sure the product
is emissions legal or emissions certifi ed for street
use. All street-legal nonstock performance parts
will be assigned an EO (executive order) exemption
number by CARB (the California Air Resources
Board). Products without this exemption number are
not street legal.
EEPROM Programming Using Computerized
Equipment
Most newer computers use Electrically Erasable
Programmable Read Only Memory (EEPROM) or
Flash Erasable Programmable Read Only Memory
(FEPROM) chips that are permanently soldered to
the circuit board. These chips must be programmed
using electronic equipment. They are often repro-
grammed to correct driveability and performance
problems.
EEPROMs are programmed using a method
referred to as fl ash programming. Flash program-
ming may be performed by downloading the
vehicle’s information through a computer, a com-
puterized diagnostic analyzer, or a scan tool. Actual
programming details vary between manufacturers,
but the basic procedure begins by placing the com-
puter in the programming mode. One of two meth-
ods is used to program the computer:
• Direct programming using a service computer
or a laptop computer, Figure 25-12.
• Remote programming with the computer off
the vehicle.
Direct Programming
Direct programming is the fastest and simplest
method. The new information is downloaded by
attaching a shop recalibration device (usually a lap-
top computer) directly to the data link connector. The
erasure and programming is done by accessing the
programming menu and following the instructions
as prompted by the computer. Then, the vehicle’s
operating information and parameters are entered
into the vehicle’s computer through the connector.
Remote Programming
Remote programming is done with the vehicle’s
computer removed from the vehicle. This procedure
is used when changes need to be made through a
direct modem connection to a manufacturer’s data-
base computer. It can also be done in cases where
direct programming is not practical or possible.
Since special connectors and tools are required for
this type of programming, this procedure is done
only at new vehicle dealerships.
EEPROM Programming Procedure
To begin programming the EEPROM-equipped
computer, make sure that the vehicle’s battery is fully
charged. Recharge the battery if necessary. Do not
charge the battery during the programming procedure,
as damage to the computer will result. Connect the pro-
gramming computer or scan tool to the data link con-
nector. Make any other vehicle connections as needed
before proceeding with the programming sequence.
CAUTION
Do not disconnect the scan tool or
programming computer from the data
link connector during the programming
sequence. Doing so will damage the vehicle’s
computer.
To start the programming sequence, the program-
ming computer prompt may ask you to enter the
engine type, vehicle type, and vehicle identifi cation
number (VIN) in a specifi c sequence. Once the vehi-
cle information is entered, go to the programming
software and follow the directions as prompted.