Pontiac Fiero 1988 Service Manual page 434

DRIVEABILITY AND EMISSIONS - FUEL INJECTION 6 E 7
On engines that can be monitored in the open
mode, it allows certain parameters to be obtained
without changing the engine o p e r a t i n g
characteristics. The parameters capable of being read
vary from engine family to engine family. Most
"Scan" tools are programmed so that the system will
go directly into the special mode if the "open" mode is
not available.
ALDL (1 OK, or Special) Mode
( n o t used o n all engines)
In this mode, all information incorporated into a
specific engine and ECM is obtainable. However, in
this mode the system operating characteristics are
modified as follows.
• "Closed Loop" timers are bypassed
• EST (spark) is advanced
• I AC will control engine idle to 1000 rpm ±
50 rpm (if applicable)
• On some engines, canister purge solenoid will
be enabled
• P/N restrict functions will be disabled.
Factory Test (Back-up or 3 . 9 K) M o d e
(TBI, Port)
In this mode, the ECM is operating on the fuel
back-up logic and is calibrated by the Calpak or Mem-
cal. These are used to control the fuel delivery if the
ECM fails. This mode verifies that the back-up feature
is OK. The parameters that can be read on a "Scan"
tool in this mode are not of much use for service.
"SCAN" TOOL LIMITATIONS AND USE
The "Scan" tool allows a quick check of sensors
and switches which are inputs to the ECM. However,
on some applications the data update rate makes the
tool less effective as a voltmeter when trying to detect
an intermittent which lasts for a very short time.
However, the "Scan" tool allows one to manipulate
wiring harnesses or components under the hood while
observing the "Scan" readout. This helps in locating
intermittents with the engine not running.
Intermittent Conditions
The "Scan" tool is helpful in cases of intermittent
operation. The tool can be plugged in and observed
while driving the vehicle under the condition where
the light comes "ON" momentarily, or the engine
driveability is poor momentarily. If the problem
seems to be related to certain areas that can be
checked on the "Scan" tool, then those are the
positions that should be checked while driving the
vehicle. If there does not seem to be any correlation
between the problem and any specific circuit, the
"Scan" tool can be checked on each position, watching
for a period of time to see if there is any change in the
readings that indicates intermittent operation.
The "Scan" tool is also a useful and quick way of
comparing operating parameters of a poorly operating
engine with a known good one. For example; A sensor
may shift in value but not set a code. Comparing with
a known good vehicle may uncover the problem.
The "Scan" tool has the ability to save time in
diagnosis and prevent the replacement of good parts.
The key to using the "Scan" tool successfully for
diagnosis lies in the technician's ability to understand
the system he is trying to diagnose as well as an
understanding of the "Scan" tool's limitations.
Therefore, the technician should read the tool
manufacturer's operating manual to become familiar
with the operation. The following information will
describe most of the "Scan" tool positions and how
they can be helpful in diagnosis.
"SCAN" TOOL POSITIONS
The following positions may not be applicable to
all engines. See the facing page of the diagnostic
circuit check for a particular engine to decide which
positions apply to that engine.
Mode
Check with the manufacturer to determine what
the function of this mode is. In most cases it allows the
user to place the ECM in different operating modes.
Injector Pulse Width
In this position, the reading is given in
milliseconds, which is the "ON" time that the ECM is
commanding to the injector(s).
Closed Loop/Open Loop
This position will indicate whether the engine
control system is operating in "Open Loop" or "Closed
Loop". Most systems go "Closed Loop" after a certain
amount of running time, when coolant temperature is
high enough, and the oxygen sensor becomes active.
Exhaust (Rich/Lean Indicator)
This indicates the O2 sensor voltage at the instant
that the data stream is sampled. If voltage is less than
350 mv, the value will be lean. If above 550 mv, a rich
exhaust is indicated.
Trouble Codes
This will display any trouble codes stored in the
ECM memory.