Page 1377 of 3051
Wiring DiagramNLEC1794MODELS WITH ECM IN ENGINE COMPARTMENTNLEC1794S03
YEC745
HEATED OXYGEN SENSOR 1 HEATER (FRONT)SR20DE
Wiring Diagram
EC-952
Page 1378 of 3051
MODELS WITH ECM IN CABINNLEC1794S04
YEC932
HEATED OXYGEN SENSOR 1 HEATER (FRONT)SR20DE
Wiring Diagram (Cont'd)
EC-953
Page 1379 of 3051
Diagnostic ProcedureNLEC1795
1 CHECK OVERALL FUNCTION
1. Turn ignition switch ªONº.
2. Set the tester probe between ECM terminals 4 [HO2S1 Heater (front) signal] and ground.
3. Start engine and let it idle.
4. Check the voltage under the following conditions.
SEF239Z
OK or NG
OK©INSPECTION END
NG©GO TO 2.
2 CHECK POWER SUPPLY
1. Turn ignition switch ªOFFº.
2. Disconnect heated oxygen sensor 1 (front) harness connector.
SEF774Z
3. Turn ignition switch ªONº.
4. Check voltage between HO2S1 terminal 1 and ground with CONSULT-II or tester.
SEF934X
OK or NG
OK©GO TO 4.
NG©GO TO 3.
HEATED OXYGEN SENSOR 1 HEATER (FRONT)SR20DE
Diagnostic Procedure
EC-954
Page 1380 of 3051

3 DETECT MALFUNCTIONING PART
Check the following.
+Harness connectors F38, M50 (where fitted)
+Harness connectors M72, F44 (where fitted)
+10A fuse
+Harness for open or short between heated oxygen sensor 1 (front) and fuse
©Repair harness or connectors.
4 CHECK GROUND CIRCUIT
1. Turn ignition switch ªOFFº.
2. Disconnect ECM harness connector.
3. Check harness continuity between HO2S1 terminal 3 and ECM terminal 4.
Refer to wiring diagram.
Continuity should exist.
4. Also check harness for short to ground and short to power.
OK or NG
OK©GO TO 5.
NG©Repair open circuit or short to ground or short to power in harness or connectors.
5 CHECK HEATED OXYGEN SENSOR 1 HEATER (FRONT)
Refer to ªComponent Inspectionº, EC-955.
OK or NG
OK©GO TO 6.
NG©Replace heated oxygen sensor 1 (front).
6 CHECK INTERMITTENT INCIDENT
Perform ªTROUBLE DIAGNOSIS FOR INTERMITTENT INCIDENTº, EC-670.
©INSPECTION END
SEF935X
Component InspectionNLEC1796HEATED OXYGEN SENSOR 1 HEATER (FRONT)NLEC1796S01Check resistance between terminals 3 and 1.
Resistance: 2.3 - 4.3Wat 25ÉC (77ÉF)
Check continuity between terminals 2 and 1, 3 and 2.
Continuity should not exist.
If NG, replace the heated oxygen sensor 1 (front).
CAUTION:
+Discard any heated oxygen sensor which has been
dropped from a height of more than 0.5 m (19.7 in) onto a
hard surface such as a concrete floor; use a new one.
+Before installing new oxygen sensor, clean exhaust sys-
tem threads using Oxygen Sensor Thread Cleaner tool
and approved anti-seize lubricant.
HEATED OXYGEN SENSOR 1 HEATER (FRONT)SR20DE
Diagnostic Procedure (Cont'd)
EC-955
Page 1381 of 3051

SEF327R
Component DescriptionNLEC1797The heated oxygen sensor 2 (rear), after three way catalyst, moni-
tors the oxygen level in the exhaust gas.
Even if switching characteristics of the heated oxygen sensor 1
(front) are shifted, the air fuel ratio is controlled to stoichiometric,
by the signal from the heated oxygen sensor 2 (rear).
This sensor is made of ceramic zirconia. The zirconia generates
voltage from approximately 1V in richer conditions to 0V in leaner
conditions.
Under normal conditions the heated oxygen sensor 2 (rear) is not
used for engine control operation.
CONSULT-II Reference Value in Data Monitor
Mode
NLEC1798Specification data are reference values.
MONITOR ITEM CONDITION SPECIFICATION
HO2S2 (B1)
+Engine: After warming upRevving engine from idle to 3,000
rpm0 - 0.3V¨Approx. 0.6 - 1.0V
HO2S2 MNTR
(B1)LEAN¨RICH
ECM Terminals and Reference ValueNLEC1799Specification data are reference values and are measured between each terminal and ground.
CAUTION:
Do not use ECM ground terminals when measuring input/output voltage. Doing so may result in dam-
age to the ECM's transistor. Use a ground other than ECM terminals, such as the ground.
TERMI-
NAL
NO.WIRE
COLORITEM CONDITION DATA (DC Voltage)
63 LHeated oxygen sensor 2
(rear)[Engine is running]
+After warming up to normal operating tempera-
ture and engine speed is 3,000 rpm0 - Approximately 1.0V
HEATED OXYGEN SENSOR 2 (REAR)SR20DE
Component Description
EC-956
Page 1382 of 3051
Wiring DiagramNLEC1800MODELS WITH ECM IN ENGINE COMPARTMENTNLEC1800S03
YEC746
HEATED OXYGEN SENSOR 2 (REAR)SR20DE
Wiring Diagram
EC-957
Page 1383 of 3051
MODELS WITH ECM IN CABINNLEC1800S04
YEC933
HEATED OXYGEN SENSOR 2 (REAR)SR20DE
Wiring Diagram (Cont'd)
EC-958
Page 1384 of 3051
Diagnostic ProcedureNLEC1801
1 CHECK OVERALL FUNCTION-I
1. Start engine and drive the vehicle at over 70 km/h (43 MPH) for 2 consecutive minutes.
2. Stop vehicle and keep the engine running.
3. Set voltmeter probes between ECM terminals 63 [HO2S2 (B1) signal] and ground.
4. Check the voltage while revving up to 4,000 rpm under no load at least 10 times.
(Depress and release the accelerator pedal as quickly as possible.)
SEF240Z
OK or NG
OK©INSPECTION END
NG©GO TO 2.
2 CHECK OVERALL FUNCTION-II
Keep engine at idle for 10 minutes, then check the voltage between ECM terminal 63 and ground, or check the voltage
when coasting at 80 km/h (50 MPH) in ªDº position with ªSPORTS MODE SWº OFF.
SEF240Z
OK or NG
OK©INSPECTION END
NG©GO TO 3.
HEATED OXYGEN SENSOR 2 (REAR)SR20DE
Diagnostic Procedure
EC-959