P0140

COMPONENT DESCRIPTION
The rear heated oxygen sensor (Rear HO2S), after three-way catalyst, monitors the oxygen level in the exhaust gas. Even if switching characteristics of the front heated oxygen sensor are shifted, the air fuel ratio is controlled to stoichiometric, by the signal from the rear heated oxygen sensor.
This sensor is made of ceramic zirconia. The zirconia generates voltage from approximately 1 V in richer conditions to 0 V in leaner conditions.
Under normal conditions the rear heated oxygen sensor is not used for engine control operation.

CONSULT REFERENCE VALUE IN DATA MONITOR MODE
Specification data are reference values

ECM TERMINALS AND REFERENCE VALUE
Specification data are reference values and are measured between each terminal and engine ground.

ON BOARD DIAGNOSIS LOGIC
The rear heated oxygen sensor has a much longer switching time between rich and lean than the front heated oxygen sensor. The oxygen storage capacity before the three way catalyst causes the longer switching time. To judge the malfunctions of rear heated oxygen sensor, ECM monitors whether or not the voltage is too high during various driving conditions such as fuel-cut.

DIAGNOSTIC TROUBLE CODE CONFIRMATION PROCEDURE

NOTE: If "DIAGNOSTIC TROUBLE CODE CONFIRMATION PROCEDURE" has been previously conducted, always turn ignition switch "OFF" and wait at least 5 seconds before conducting the next test.

With Consult
1. Turn ignition switch "ON" and select "DATA MONITOR" mode with CONSULT.
2. Start engine and drive vehicle at a speed of more than 70 KPH (43 MPH) for 2 consecutive minutes.
3. Maintain the following condition for at least 5 consecutive seconds.
CMPS.RPM (REF): 2,000 - 2,750 rpm
VHCL SPEED SE: 64 - 120 KPH (40 - 75 MPH)
B/FUEL SCHDL: 0.75-4 msec
COOLAN TEMP/S: 70 - 100°C (158 - 212°F)
Selector lever: Suitable position
4. If 1st trip DTC is detected, go to "DIAGNOSTIC PROCEDURE".

OR

OVERALL FUNCTION CHECK
Use this procedure to check the overall function of the rear heated oxygen sensor circuit. During this check, a 1st trip DTC might not be confirmed.

WIRING DIAGRAM

DIAGNOSTIC PROCEDURES

COMPONENT INSPECTION

With Consult
1. Start engine and drive vehicle at a speed of more than 70 KPH (43 MPH) for 2 consecutive minutes.
2. Stop vehicle with engine running.
3. Select "FUEL INJECTION" in "ACTIVE TEST" mode, and select "RR O2 SENSOR" as the monitor item with CONSULT.
4. Check "RR O2 SENSOR" at idle speed when adjusting "FUEL INJECTION" to +/-25%.
"RR O2 SENSOR" should be above 0.48 V at least once when the "FUEL INJECTION" is +25%.
"RR O2 SENSOR" should be below 0.43 V at least once when the "FUEL INJECTION" is -25%.

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.

OR

Without Consult
1. Start engine and drive vehicle at a speed of more than 70 KPH (43 MPH) for 2 consecutive minutes.
2. Stop vehicle with engine running.
3. Set voltmeter probes between ECM terminal (52) (sensor signal) and engine ground.
4. Check the voltage when revving up to 4,000 rpm under no load at least 10 times.
(Depress and release accelerator pedal as soon as possible.)
The voltage should be above 0.48 V at least once. If the voltage is above 0.48 V at step 4, step 5 is not necessary.
5. Check the voltage when revving up to 6,000 rpm under no load. Or keep vehicle at idling for 10 minutes, then check the voltage. Or check the voltage when coasting from 80 KPH (50 MPH) in 3rd gear position (M/T), D position with "O/D" OFF (A/T). The voltage should be below 0.43 V at least once.

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.