Pontiac Fiero 1988 Service Manual page 507

6E2-A-52 DRIVEABILITY AND EMISSIONS - FUEL INJECTION (TBI)
CODE 45
OXYGEN SENSOR CIRCUIT
(RICH EXHAUST INDICATED)
2.5L "P" SERIES (TBI)
Circuit Description:
The ECM supplies a voltage of about .45 volt between terminals "B2" and
"B23".
(If measured with a 10
megohm digital voltmeter, this may read as low as .32 volts.) The O2 sensor varies the voltage within a range of
about 1 volt, if the exhaust is rich, down through about .10 volt, if exhaust is lean.
The sensor is like an open circuit and produces no voltage, when it is below about
3 6 0 ° C (600°F).
An open
sensor circuit, or cold sensor, causes "Open Loop" operation.
Test Description:
Numbers below refer to circled
numbers on the diagnostic chart.
1. Code 45 is set, when the O2 sensor signal voltage
on
CKT
412:
• Remains above .7 volt for 30 seconds or more;
and in "Closed Loop".
• Engine time after start is 1 minute or more.
• Throttle angle between 3% and 45%.
Diagnostic Aids:
The Code 45, or rich exhaust, is most likely caused
by one of the following:
• Fuel
Pressure - System will go rich, if pressure
is
too high. The ECM can compensate for some
increase. However, if it gets too high, a Code 45
will be set. See Fuel System diagnosis CHART
A-7.
• Leaking Injector - See CHART A-7.
• HEI Shielding - An open ground CKT 453 may
result in EMI, or induced electrical
"noise".
The
ECM looks at this "noise" as reference pulses. The
additional pulses result in a
higher
than actual
engine
speed signal. The ECM then delivers too
much fuel, causing system to go rich. Engine
tachometer will, also, show higher
than
actual
engine speed, which can help in diagnosing
this
problem.
• Canister Purge - Check for fuel saturation. If full
of fuel, check canister control and hoses. See
Canister Purge, Section "C3".
- MAP Sensor - An output that causes the ECM to
sense a higher than normal manifold pressure
(low vacuum) can cause the system to go rich.
Disconnecting the MAP sensor will allow the
ECM to set a fixed value for the MAP sensor.
Substitute a different MAP sensor, if the rich
condition is gone while the sensor is disconnected.
0
TPS - An intermittent TPS output will cause the
system to go rich, due to a false indication of the
engine accelerating.
o O? Sensor Contamination - Inspect Oxygen Sensor
for silicone contamination from fuel, or use of
improper RTV sealant. The sensor may have a
white, powdery coating and result in a high, but
false signal voltage (rich exhaust indication). The
ECM
will
then reduce the amount of fuel delivered
to the engine, causing a severe surge driveability
problem.
• EGR Valve - An EGR staying open at idle usually
accompanied by a rough idle complaint.
If Code 45 is intermittent, refer to Section "B".