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Diagnosis & Repair

WARNING: This page is about a different car, the 2002 Toyota Tundra. However, it is still accessible from the selected car via links, so may be relevant.
  1. Remove glove box and heater duct (if necessary) 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. 4 (Yellow wire) at ECM electrical connector E6. See Figure. This is the HTAF1 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.
  2. Turn ignition off. Disconnect electrical connector for A/F sensor. A/F sensor is located on exhaust pipe in front of catalytic converter. Using ohmmeter, check resistance for heater on A/F sensor between +B and HT terminals on electrical connector for A/F sensor. See Figure. Resistance should be .8-1.4 ohms at 68°F (20°C) and 1.8-3.2 ohms at 1472°F (800°C). If resistance is within specification, go to next step. If resistance is not within specification, replace A/F sensor. See AIR/FUEL SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION - V6 & V8 article.
  3. Check for defective wiring harness and electrical connectors between EFI main relay and A/F sensor, and between A/F sensor and ECM. 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.
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