Pontiac Fiero 1988 Service Manual page 609

6E3-A-26 DRIVABILITY AND EMISSIONS - FUEL INJECTION (PORT)
ECM
2-20-87
7-8-87 4S 0790-6E
CODE 13
OXYGEN SENSOR CIRCUIT
(OPEN CIRCUIT)
2.8L "P" SERIES (PORT)
Circuit Description:
The ECM supplies a voltage of about .45 volt between terminals "D7" and "D6". (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 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 13 WILL SET:
• Engine at normal operating temperature
• At least 2 minutes engine time after start
• O2 signal voltage steady between .35 and .55
volts
• RPM above 1600
• Throttle position sensor signal above 12%
(about .5 volts above closed throttle voltage)
• All conditions must be met for about 20
seconds.
If the conditions for a Code 13 exist, the
system will not go "Closed Loop".
2. This will determine if the sensor is at fault, or the
wiring or ECM is the cause of the Code 13.
3 In doing this test, use only a high impedence
digital volt ohm meter. This test checks the
continuity of CKTs 412 and 413, because if CKT
413 is open the ECM voltage on CKT 412 will be
over .6 volts (600 mV).
Diagnostic Aids:
Normal "Scan" voltage varies between 100 mV to
999 mV (.1 and 1.0 volt) while in "Closed Loop". Code
13 sets in one minute if voltage remains between .35
and .55 volts, but the system will go "Open Loop" in
about 15 seconds.
Refer to "Intermittents" in Section "B".