4Runner 4.0L
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- A heated Air/Fuel (A/F) sensor is used on each exhaust pipe in front of catalytic converter and a heated oxygen sensor is used on each exhaust pipe behind catalytic converter. For testing of A/F sensors, see AIR/FUEL SENSOR . Heated oxygen sensor on passenger side exhaust pipe behind catalytic converter may also be referred to as bank No. 1 sensor No. 2. Heated oxygen sensor on driver side exhaust pipe behind catalytic converter may also be referred to as bank No. 2 sensor No. 2.
- To test heater on heated oxygen sensor, disconnect electrical connector at appropriate heated oxygen sensor and note heated oxygen sensor terminals. See Fig 1.
- Using ohmmeter, check resistance between +B and HT terminals on electrical connector. See Fig 1. Replace heated oxygen sensor if resistance is not 11-16 ohms at 68°F (20°C). See HEATED OXYGEN SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL & INSTALLATION - V6 & V8 article.
- To check that heater is not shorted, using ohmmeter, check that no continuity exists between E1 and HT terminals on electrical connector. See Fig 1. Replace heated oxygen sensor if continuity exists. See HEATED OXYGEN SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL & INSTALLATION - V6 & V8 article.
- If problem exists in heated oxygen sensor, heater or wiring circuit, a Diagnostic Trouble Code (DTC) may be stored in Engine Control Module (ECM). See TESTING PROCEDURE under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article for retrieving of DTCs.