Front Heated Oxygen Sensor

OVERALL FUNCTION CHECK
Use this procedure to check the overall function of the front 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 "MANU TRIG" and "HI SPEED" in "DATA MONITOR" mode with CONSULT, and select "FR 02 SENSOR" and "FR O2 MNTR".
(3) Hold engine speed at 2,000 rpm under no load during the following steps.
(4) Touch "RECORD" on CONSULT screen.
(5) Check the following.




- "FR O2 MNTR" in "DATA MONITOR" mode changes from "RICH" to "LEAN" to "RICH" 5 times in 10 seconds.
5 times (cycles) are counted as shown below:

cycle | 1 | 2 | 3 | 4 | 5 |
FR O2 MNTR R-L-R-L-R-L-R-L-R-L-R

R = "FR O2 MNTR", "RICH"
L = "FR O2 MNTR", "LEAN"

- "FR O2 SENSOR" voltage goes above O.6V at least once.
- "FR O2 SENSOR" voltage goes below 0.35V at least once.

OR

Without Scan Tools
(1) Start engine and warm it up sufficiently.




(2) Set voltmeter probes between ECM terminal (46) (sensor signal) and (43) (engine ground).
(3) Check the following with engine speed held at 2,000 rpm constant under no load.
- Malfunction indicator lamp goes on more than 5 times within 10 seconds in Diagnostic Test Mode II (FRONT HEATED OXYGEN SENSOR MONITOR).
- The maximum voltage is over O.6V at least one time.
- The minimum voltage is below 0.35V at least one time.

CIRCUIT DIAGRAM





DIAGNOSTIC PROCEDURE








COMPONENT INSPECTION




Front heated oxygen sensor heater
Check resistance between terminals (3) and (1).

Resistance: 2.3 - 4.3 Ohms at 25°C (77°F)

Check continuity between terminals (2) and (1), (3) and (2).

Continuity should not exist.

If NG, replace the front 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.