Non-California Models

DESCRIPTION
The rear heated oxygen sensor (Rear HO2S), after the three way catalyst, monitors the oxygen level in the exhaust gas. This sensor is made of ceramic titania. The electric resistance of ceramic titania drastically changes at the ideal air-fuel ratio. The output voltage of the sensor, depending on its resistance, is approximately 0 to 2.2 Volts.
The ECM supplies the sensor with approximately 2 Volts and then measures the output voltage. About 0 Volts means lean and about 2 Volts means rich.
The rear heated oxygen sensor is not directly used to control the engine system.
It is used only for the on-board diagnosis of three way catalyst.




ON-BOARD DIAGNOSIS LOGIC
The rear heated oxygen sensor has a much longer switching time between rich and lean than the front oxygen sensor *1. 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 the sensor's voltage value and the switching response during the various driving condition such as fuel-cut.

*1: Front heated oxygen sensor (California models)
Front oxygen sensor (Non-California models)

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

WITH CONSULT
1. Start engine and warm it up sufficiently.




2. Select "FUEL INJECTION" in "ACTIVE TEST" mode, and select "RR 02 SENSOR" as the monitor item with CONSULT.
3. Check "RR 02 SENSOR" at idle speed when adjusting "FUEL INJECTION" to ±25%.

"RR O2 SENSOR" should be above O.48V (California models), O.60V (Non-California models) at least once when the "FUEL INJECTION" is +25%.
"RR O2 SENSOR" should be below O.43V (California models), O.55V (Non-California models) at least once when the "FUEL INJECTION" is -25%.

OR

WITH NO TOOLS
1. Start engine and warm it up sufficiently.




2. Set voltmeter probes between ECM terminals (52) (sensor signal) and (43) (engine 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 O.48 Volts at least once. If the voltage is above O.48 Volts 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 O.43 Volts at least once.

NOTE:
- After starting the engine, the output voltage of the rear heated oxygen sensor indicates higher voltage (approx. 5 Volts at highest) than the normal operating range for about 7 seconds. This is due to checking for open circuits in rear heated oxygen sensor by on-board diagnosis. Therefore, if you measure the voltage (at ECM terminal 52) during this diagnosis, the higher voltage will appear. (CONSULT will also show the higher voltage, GST may show approx. O Volts.) This is not a malfunction even though it is out of the normal range.




WIRING DIAGRAM




DIAGNOSTIC PROCEDURE

COMPONENT INSPECTION




Check resistance between terminals (a) and (c).

Resistance: 5.2 - 8.2 Ohms at 25°C (77°F)

If NG, replace the rear heated oxygen sensor.

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.