Pontiac Fiero 1988 Service Manual page 505

6E2-A-50 D R I V E A B I L I T Y A N D E M I S S I O N S - FUEL INJECTION (TBI)
5-6-87
412 PPL
413 TAN
OXYGEN ( 0
2
) SENSOR
A
ENGINE
GROUND
B2
B23
EXHAUST
ECM
0
2
S E N S O R
SIGNAL
4-6-87
* 7S 3204-6E
CODE 44
OXYGEN SENSOR CIRCUIT
(LEAN 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 44 is set, when the O2 sensor signal voltage
on CKT 412:
• Remains below .2 volt for 60 seconds or more;
• And the system is operating in "Closed Loop".
Diagnostic Aids:
Using the "Scan", observe the block learn value at
different rpms. The "Scan" also displays the block
cells, so the block learn values can be checked in each
of the cells, to determine when the Code 44 may have
been set. If the conditions for Code 44 exists, the block
learn values will be around 150 or higher.
• 0.2 Sensor Wire - Sensor pigtail may be
mispositioned and contacting the exhaust
manifold.
• Check for ground in wire between connector
and sensor.
• Fuel Contamination - Water, even in small
amounts, near the in-tank fuel pump inlet can
be delivered to the injector. The water causes
a lean exhaust and can set a Code 44.
• Fuel Pressure - System will be lean if pressure
is too low. It may be necessary to monitor fuel
pressure, while driving the car at various road
speeds and/or loads to confirm. See Fuel
System diagnosis CHART A-7.
® Exhaust Leaks - If there is an exhaust leak,
the engine can cause outside air to be pulled
into the exhaust and past the sensor. Vacuum
or crankcase leaks can cause a lean condition.
• If Code 44 intermittent, refer to Section "B".