Pontiac Fiero 1988 Service Manual page 654

DRIVEABILITY AMD E M I S S I O N S - F U E L INJECTION (PORT) 6 E 3 - C 1 - 5
A problem In the O2 sensor circuit, or fuel system
should set a Code 13 (open circuit), Code 4 4 (lean
indication), or Code 45 (rich indication). Refer to
applicable chart if any of these codes were stored in
memory.
TPS
A "Scan" tool displays throttle position in volts.
The 2.8L should read less than 1.25 volts, with
throttle closed and ignition "ON," or at idle. Voltage
should increase at a steady rate as throttle is moved
toward wide open throttle (WOT).
The electronic control module (ECM) has the
ability to Auto-Zero the throttle position sensor (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. A failure in
the TPS or circuit should set a Code 21 or 22.
MAP Sensor
"Scan" displays manifold pressure in volts. Low
pressure (high vacuum) reads a low voltage while a
high pressure (low vacuum) reads a high voltage. A
failure in the manifold absolute pressure (MAP)
sensor circuit should set a Code 33 or 34 and using the
chart will find the cause of the problem. A Code 33
may be set if a rough or unstable idle exists. CHART
C-1D can also be used to check MAP sensor.
VSS
A "Scan" tools reading should closely match with
speedometer reading with drive wheels turning. A
failure in the vehicle speed sensor (VSS) circuit should
set a Code 24.
P/N S w i t c h
A "Scan" tool should read P/N when in Park, or
Neutral, and R-D, L, when in Drive or Overdrive.
This reading may vary with different makes of tools.
Refer to CHART C-1 A for P/N switch diagnosis.
A/C Request Signal
If the pressure cycling switch is closed and A/C is
"ON," the "Scan" tool should indicate A/C "ON".
See Section "CIO" for electrical system diagnosis.
Reference Signal
A "Scan" tool will read this signal and is displayed
in RPM. See Section "C4" for more information on the
Ignition System.
ON-CAR SERVICE
E L E C T R O N I C C O N T R O L M O D U L E ( E C M )
Service of the ECM should normally consist of
either replacement of the ECM or a programmable
read only memory (PROM) change.
If the diagnostic procedures call for the ECM to be
replaced, the engine calibrator (PROM) and ECM
should be checked first to see if they are the correct
parts. If they are, remove the PROM and CALPAK
from the faulty ECM and install them in the new
service ECM. THE SERVICE ECM WILL NOT
CONTAIN A PROM or CALPAK. Trouble Code 51
indicates the PROM is installed improperly or has
malfunctioned. When Code 51 is obtained, check the
PROM installation for bent pins or pins not fully
seated in the socket. If the PROM is installed correctly
and Code 51 still shows, replace the PROM.
Important
When replacing the production ECM with a
service ECM (controller), it is important to transfer
the Broadcast code and production ECM number to
the service ECM label. Please do not record on ECM
cover. This will allow positive identification of ECM
parts throughout the service life of the vehicle.
N O T I C E :
To prevent internal ECM damage, the
ignition must be "OFF" when
disconnecting or reconnecting power to
ECM (for example, battery cable, ECM
pigtail, ECM fuse, jumper cables, etc.).
See Section "8C" for console removal and
installation procedures. Section "8A" or Figure Cl-7
also shows the location of the ECM.
F i g u r e d - ? ECM
M o u n t i n g