Pontiac Fiero 1988 Service Manual page 637

6E3-A-54 DRIVABILITY AND EMISSIONS - FUEL INJECTION (PORT)
ECM
OXYGEN ( 0
2
) SENSOR
EXHAUST
ENGINE
GROUND
P P L
412
TAN 413
D7
0
2
S E N S O R
SIGNAL
0
2
GROUND
CIRCUIT
7-8-87
2-20-87
4S 0790-6E
CODE 45
OXYGEN SENSOR CIRCUIT
(RICH EXHAUST INDICATED)
2.8L "P" SERIES (PORT)
Circuit Description:
The ECM supplies a voltage of about .45 volt between terminals "D6" and "D7". (If measured with a 10
megohm digital voltmeter, this may read as low as .32 volt.) 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 1 5 ° 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 or
CKT 412
• Remains above .7 volt for 50 seconds; and in
"Closed Loop"
• Engine time after start is 1 minute or more
• Throttle angle greater than 2% (about .2 volt
above idle voltage)
Diagnostic Aids:
Using the "Scan", observe the block learn values at
different rpm conditions to determine when the Code
45 may have been set. If the conditions for Code 45
exists, The block learn values will be around 115.
Check:
• 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
may be set. See fuel system diagnosis CHART
A-7.
•
For rich injector Perform injector balance test
CHART C-2A.
• For leaking injector See CHART A-7.
• For fuel contaminated oil
• HEI shielding An open ground CKT 453
(ignition system reflow) 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 lower than normal vacuum can cause the
system to go rich. Disconnecting the MAP sensor
will allow the ECM to set a fixed value for the
sensor Substitute a different MAP sensor if the
the rich condition is gone while the sensor is
disconnected, and check for a Code 34.
• For leaking fuel pressure regulator diaphram by
checking vacuum line to regulator for fuel
• TPS An intermittent TPS output will cause the
system to go rich, due to a false indication of the
engine accelerating.