Diagnosis & Repair
WARNING: This page is about a different car, the 2002 Toyota Prius. However, it is still accessible from the selected car via links, so may be relevant.
- Remove glove box for access to ECM with electrical connectors still installed on ECM. See Figure. Turn ignition on. Using voltmeter, check voltage between body ground and terminal No. 1 (Pink/Blue wire) at ECM electrical connector E10. See Figure. This is the HT1A terminal on ECM. 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 heated oxygen sensor No. 1. Heated oxygen sensor No. 1 is located on exhaust pipe in front of catalytic converter. Using ohmmeter, check resistance between +B and HT terminals on electrical connector for heated oxygen sensor No. 1. 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 No. 1. See HEATED OXYGEN SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION - 4-CYLINDER article.
- Check wiring harness and electrical connectors between ECM and heated oxygen sensor No. 1, and between heated oxygen sensor No. 1 and EFI main relay. See WIRING DIAGRAMS article. EFI main relay may also be referred to as EFI relay. EFI main relay is located in fuse/relay box at driver's side front corner of engine compartment. Repair wiring harness or electrical connectors as necessary.