Pontiac Fiero 1988 Service Manual page 522

DRIVEABILITY AND EMISSIONS - FUEL INJECTION (TBI) 6E2-C1-5
PROM
An incorrect or faulty PROM, which is part of the
ECM, may set a Code 51.
ECM INPUTS
All of the sensors and input switches can be
diagnosed by the use of a "Scan" tool. Following is a
short description of how the sensors and switches can
be diagnosed by the use of "Scan". The "Scan" can also
by used to compare the values for a normal running
engine with the engine you're diagnosing.
Coolant Temp. Sensor
A "Scan" tool displays engine temp, in degrees
centigrade. After the engine is started, the
temperature should rise steadily to about 90°C, then
stabilize when thermostat opens. If the engine has not
been run for several hours (overnight), the coolant
temperature and MAT temperatures should read close
to each other. A fault in the coolant sensor circuit
should set a Code 14 or 15. The code charts also
contain a chart to check for sensor resistance values
relative to temperature.
MAP Sensor
A "Scan" tool reads manifold pressure and will
display either volts or kPa of pressure.
Key "ON", engine stopped, (no vacuum), MAP will
read high voltage or pressure, while at idle (high
vacuum), MAP will read low voltage or pressure.
Likewise, on accel., MAP will read high and on
decel.,will read low.
A failure in the MAP sensor, or circuit, should
result in a Code 33 or 34.
MAT
A "Scan" tool displays temperature of the air
entering the engine and should read close to ambient
air
temperaturejkwhen
engine is cold, and rise as
underhood temperature increases. If the engine has
not been run for several hours (overnight), the MAT
sensor temperatue and coolant temperature should
read close to each other. A failure in the MAT sensor
circuit should set a Code 23 or 25. The code charts also
contain a chart to check for sensor resistance values
relative to temperature.
Oxygen (O2)
Sensor
The "Scan" has several positions that will indicate
the state of the exhaust gases, O2 voltage, integrator,
and block learn. See "Scan" position information in
Introduction, Section "BE".
A problem in the O 9 sensor circuit should set a
Code 13 (open circuit). Code 44 (lean exhaust
indication), Code 45 (rich exhaust indication). Refer
to applicable chart, if any of these codes were stored in
memory.
Throttle Position Sensor (TPS)
A
"Sean"
tool
displays throttle position in volts.
The 2.5L should read below 1.25 volts, with throttle
closed and ignition "ON", or at idle. Voltage should
increase at a steady rate as throttle is moved toward
WOT.
The ECM has the ability to Auto-Zero the TPS
voltage, if it is below about 1.25 volts. This means
that any voltage less than 1.25 volts will be
determined by the ECM to be 0% throttle. Some
"Scan" tools have the ability to read the percentage of
throttle angle and should read 0%, when the throttle
is closed. A failure in the TPS, or circuit, should set a
Code 21 or 22.
VSS
A "Scan" tool reading should closely match with
speedometer reading, with drive wheels turning. A
failure in the VSS circuit should set a Code 24.
P/N Switch
A "Scan" tool should read "ON", when in park or
neutral and "OFF", when in drive. This reading may
vary with different makes of tools. Refer to CHART C-
1A for P/N switch diagnosis.
A/C Request Signal
If the low pressure switch is closed and A/C is
"ON", the "Scan" tool should indicate A/C "ON". See
Section "CIO" for A/C electrical system diagnosis.
DIS Reference Signal
A "Scan" tool will read this signal and is displayed
in rpm. See Section "C4", for more information on the
direct ignition system (DIS).