Pontiac Fiero 1988 Service Manual page 635

6E3-A-52 DRIVABILITY A N D EMISSIONS - F U E L INJECTION (PORT)
ECM
2-20-87
7-8-87 4 S 0790-6E
CODE 44
OXYGEN SENSOR CIRCUIT
(LEAN EXHAUST INDICATED)
2.8L "P" SERIES (PORT)
Circuit Description:
The ECM supplies a voltage of about .45 volt to CKT 412. (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 44 is set when the O2 sensor signal voltage
on CKT 412
• Remains below .2 volt for 20 seconds
• And the system is operating in "Closed Loop"
Diagnostic Aids:
Using the "Scan", observe the block learn values
at different rpm and air flow conditions 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.
Check:
• O2 sensor wire Sensor pigtail may be
mispositioned and contacting the exhaust
manifold.
• For intermittent ground in wire between
connector and sensor
• MAP sensor A (MAP) sensor output that
causes the ECM to sense a higher than normal
vacuum will cause the system to go lean.
Disconnect the MAP sensor, and if the lean
condition is gone, check for Code 34.
• For lean injector(s) Perform injector balance test
CHART C-2A.
• For fuel contamination Water, even in small
amounts, near the in-tank fuel pump inlet can be
delivered to the injectors. 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.
• EGR In normal operation the ECM delivers less
fuel and advances spark when EGR comes in. If
the EGR does not open, the system will go lean
and may have slight spark knock.