Diagnosis & Repair
WARNING: This page is about a different car, the 2002 Toyota Sequoia. However, it is still accessible from the selected car via links, so may be relevant.
- Remove glove box and heater duct (if necessary) for access to ECM with electrical connectors still installed on ECM. See Figure.
- Turn ignition on. For DTC P0135, using voltmeter, check voltage between body ground and terminal No. 4 (Blue wire) at ECM electrical connector E7. See Figure. This is the HTL terminal on ECM. For DTC P0155, using voltmeter, check voltage between body ground and terminal No. 3 (Blue/Red wire) at ECM electrical connector E7. See Figure. This is the HTR terminal on ECM. On either DTC, voltage should be 9-14 volts. If voltage is not within specification, go to next step. If voltage is within specification, replace ECM.
- Disconnect electrical connector for appropriate heated oxygen sensor located on exhaust manifold. Heated oxygen sensor (bank No. 1 sensor No. 1) is located on driver's side exhaust manifold and heated oxygen sensor (bank No. 2 sensor No. 1) is located on passenger's side exhaust manifold.
- Using ohmmeter, check resistance between +B and HT terminals on electrical connector for heater on appropriate heated oxygen sensor. See Fig 1. Resistance should be 11-16 ohms at 68°F (20°C). If resistance is within specification, go to next step. If resistance is not within specification, replace heated oxygen sensor. See HEATED OXYGEN SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION - V6 & V8 article.
- Check wiring harness and electrical connectors between ECM and appropriate heated oxygen sensor, and between appropriate heated oxygen sensor, EFI No. 2 fuse (10-amp) and EFI main relay. See WIRING DIAGRAMS article. EFI main relay may also be referred to as EFI relay. EFI No. 2 fuse and EFI main relay are located in fuse/relay box at driver's side front corner of engine compartment.