DTC 0512

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 1V in richer conditions to 0V 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 (25) (ECCS 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 the various driving condition such as fuel-cut.


DIAGNOSTIC TROUBLE CODE CONFIRMATION PROCEDURE

CAUTION: Always drive vehicle at a sate speed.

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.

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.






Without TOOLS
(1) Start engine and warm it up to normal operating temperature.
(2) Set voltmeter probes between ECM terminals (56) (sensor signal) and (25) (engine ground).
(3) Check the voltage after racing 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 below 2V during this procedure.







Electrical Diagrams






Circuit Connectors






DIAGNOSTIC PROCEDURE


COMPONENT INSPECTION
Rear heated oxygen sensor









Without TOOLS
(1) Start engine and warm it up to normal operating temperature.
(2) Set voltmeter probes between ECM terminals (56) (sensor signal) and (25) (ECM ground).
(3) Check the voltage when racing 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 0.48V at least once. If the voltage is above 0.48V at step 3, step 4 is not necessary.

(4) Check the voltage when racing 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 km/h (50 MPH) in 3rd gear position.
The voltage should be below 0.43V at least once.