Pontiac Fiero 1988 Service Manual page 652

D R I V E A B I L I T Y A N D E M I S S I O N S - F U E L I N J E C T I O N (PORT) 6 E 3 - C 1
-3
y.—Tf
1 3
EXHAUST O X Y G E N ( 0
2
)
SENSOR
10-2-86
* 4S 0078-6E
Figure C1-5 Exhaust Oxygen (O2) Sensor
A failure in the manifold absolute pressure (MAP)
sensor circuit should set a Code 33 or Code 34.
O x y g e n (O2) S e n s o r
The exhaust oxygen sensor is mounted in the
exhaust system where it can monitor the oxygen
content of the exhaust gas stream. The oxygen content
in the exhaust reacts with the oxygen sensor to
produce a voltage output. This voltage ranges from
approximately .1 volts (high O2 - lean mixture) to .9
volts (low 02 - rich mixture).
By monitoring the voltage output of the O2 sensor,
the electronic control module (ECM) will know what
fuel mixture command to give to the injectors (lean
mixture-low voltage-rich command, rich mixture-high
voltage-lean command).
The O2 sensor circuit, if open, should set a Code
13. A shorted sensor circuit should set a Code 44. A
high voltage in the circuit should set a Code 45. When
any of these codes are set, the car should run in the
"Open Loop" mode.
Throttle Position S e n s o r (TPS)
The throttle position sensor (TPS) is connected to
the throttle shaft on the throttle body (see Figure Cl-
6) It is a potentiometer with one end connected to 5
volts from the ECM and the other to ground. A third
wire is connected to the ECM to measure the voltage
from the TPS. As the throttle valve angle is changed
(accelerator pedal moved), the output of the TPS also
changes. At a closed throttle position, the output of the
TPS is low. As the throttle valve opens, the output
increases so that, at wide open throttle, the output
voltage should be approximately 5 volts.
By monitoring the output voltage from the TPS,
the ECM can determine fuel delivery based on throttle
valve angle (driver demand).
Failure in the TPS circuit will set a Code 22 (low
voltage) or Code 21 (voltage too high).
17 N-m
(12.5 F T . LBS.)
fTI T H R O T T L E B O D Y [ 4 ] A I R P L E N U M
[T1
T.P.S. [ j f ] C O L D S T A R T V A L V E A I R T U B E
f T I G A S K E T
f 6 l l . A . C V A L V E
551919-61
Figure C1-6 Throttle Position Sensor
Park/Neutra! S w i t c h ( A u t o T r a n s . Only)
The Park/Neutral (P/N) switch indicates to the
ECM when the transmission is in Park or Neutral.
This information is used for the
transmission/transaxle converter clutch (TCC)
system, IAC valve operation, and exhaust gas
recirculation (EGR) control.
N O T I C E :
Vehicle should not be driven with
Park/Neutral switch disconnected as idle
quality may be affected.
An inoperative P/N switch could cause improper
idle speed or TCC operation. See Section "8A" for
more information on the P/N switch.
A/C " O n " Signal
This signal tells the ECM that the A/C selector
switch is turned "ON", and that the pressure cycling
switch is closed. The ECM uses this to adjust the idle
speed before turning on the A/C relay and to
determine when A/C is requested. The ECM has total
control of the A/C clutch.
Vehicle S p e e d S e n s o r
The Vehicle Speed Sensor (VSS) sends a pulsing
voltage signal to the ECM, which the ECM converts to
miles per hour. This sensor mainly controls the
operation of the TCC system. See Section "C8" TCC
System for more information.
Distributor R e f e r e n c e Signal
The distributor sends a signal to the ECM to tell it
both engine rpm and crankshaft position. See Section
"C4" EST system for further information.