Page 849 of 3051
Diagnostic ProcedureNLEC1229
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.
SEF012XA
3. Turn ignition switch ªONº.
4. Check voltage between 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)QG18DE
Diagnostic Procedure
EC-424
Page 850 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 OUTPUT SIGNAL CIRCUIT
1. Turn ignition switch ªOFFº.
2. Disconnect ECM harness connector.
3. Check harness continuity between heated oxygen sensor 1 (front) harness connector 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-425.
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-145.
©INSPECTION END
SEF935X
Component InspectionNLEC1230HEATED OXYGEN SENSOR 1 HEATER (FRONT)NLEC1230S01Check 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)QG18DE
Diagnostic Procedure (Cont'd)
EC-425
Page 851 of 3051

SEF327R
Component DescriptionNLEC1231The 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
NLEC1232Specification 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 ValueNLEC1233Specification 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)QG18DE
Component Description
EC-426
Page 852 of 3051
Wiring DiagramNLEC1237MODELS WITH ECM IN ENGINE COMPARTMENTNLEC1237S03
YEC746
HEATED OXYGEN SENSOR 2 (REAR)QG18DE
Wiring Diagram
EC-427
Page 853 of 3051
MODELS WITH ECM IN CABINNLEC1237S04
YEC895
HEATED OXYGEN SENSOR 2 (REAR)QG18DE
Wiring Diagram (Cont'd)
EC-428
Page 854 of 3051
Diagnostic ProcedureNLEC1238
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 3rd gear.
SEF240Z
OK or NG
OK©INSPECTION END
NG©GO TO 3.
HEATED OXYGEN SENSOR 2 (REAR)QG18DE
Diagnostic Procedure
EC-429
Page 855 of 3051
3 RETIGHTEN GROUND SCREWS
1. Turn ignition switch ªOFFº.
2. Loosen and retighten engine ground screws.
JEF104Y
©GO TO 4.
4 CHECK INPUT SIGNAL CIRCUIT
1. Turn ignition switch ªOFFº.
2. Disconnect heated oxygen sensor 2 (rear) harness connector and ECM harness connector.
SEF639Z
3. Check harness continuity between ECM terminal 63 and heated oxygen sensor 2 (rear) harness connector terminal 1.
Refer to wiring diagram.
Continuity should exist.
4. Check harness continuity between ECM terminal 63 [or heated oxygen sensor 2 (rear) harness connector terminal 1]
and ground.
Continuity should not exist.
5. Also check harness for short to ground and short to power.
OK or NG
OK©GO TO 6.
NG©GO TO 5.
5 DETECT MALFUNCTIONING PART
Check the harness for open or short between heated oxygen sensor 2 (rear) and ECM.
©Repair open circuit or short to ground or short to power in harness or connectors.
HEATED OXYGEN SENSOR 2 (REAR)QG18DE
Diagnostic Procedure (Cont'd)
EC-430
Page 856 of 3051

6 CHECK GROUND CIRCUIT
1. Check harness continuity between heated oxygen sensor 2 (rear) harness connector terminal 4 and body ground.
Refer to wiring diagram.
Continuity should exist.
2. Also check harness for short to power.
OK or NG
OK©GO TO 7.
NG©Repair open circuit or short to power in harness or connectors.
7 CHECK HEATED OXYGEN SENSOR 2 (REAR)
Refer to ªComponent Inspectionº, EC-431.
OK or NG
OK©GO TO 8.
NG©Replace heated oxygen sensor 2 (rear).
8 CHECK INTERMITTENT INCIDENT
Perform ªTROUBLE DIAGNOSIS FOR INTERMITTENT INCIDENTº, EC-145.
©INSPECTION END
SEF662Y
Component InspectionNLEC1239HEATED OXYGEN SENSOR 2 (REAR)NLEC1239S01With CONSULT-II
1) Start engine and drive vehicle at a speed of more than 70 km/h
(43 MPH) for 2 consecutive minutes.
2) Stop vehicle with engine running.
3) Select ªFUEL INJECTIONº in ªACTIVE TESTº mode, and
select ªHO2S2 (B1)º as the monitor item with CONSULT-II.
4) Check ªHO2S2 (B1)º at idle speed when adjusting ªFUEL
INJECTIONº to±25%.
ªHO2S2 (B1)º should be above 0.68V at least once when
the ªFUEL INJECTIONº is +25%. ªHO2S2 (B1)º should be
below 0.56V at least once when the ªFUEL INJECTIONº is
þ25%.
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.
SEF244YA
HEATED OXYGEN SENSOR 2 (REAR)QG18DE
Diagnostic Procedure (Cont'd)
EC-431