Diagnosis & Repair
WARNING: This page is about a different car, the 2002 Lexus ES 300. However, it is still accessible from the selected car via links, so may be relevant.
- Access ECM behind glove box. Turn ignition on. Using DVOM, backprobe at ECM harness connector and measure voltage between terminal No. 28 (Brown wire) at ECM connector E10 and terminals No. 4 (Black/White wire) and No. 3 (Black/Red wire) at ECM harness connector E9. See Figure. If both voltages are 9-14 volts, replace ECM. If either voltage is not 9-14 volts, go to next step.
- Disconnect suspect A/F sensor harness connector. Measure resistance between terminal No. 2 (Black wire on bank No. 1; Black/White wire on bank No. 2) and terminal No. 1 (Black/White wire on bank No. 1; Black/Red wire on bank No. 2) at A/F sensor connector (component side). See Figure. Resistance should be 1.8-3.4 ohms at 68°F (20°C) and 5.0-7.5 ohms at 932°F (500°C). If resistances are not as specified, replace appropriate A/F sensor. If resistances are as specified, go to next step.
- Check EFI ECU relay. See Fig 1. Replace relay as necessary. If relay is okay, check for open or short in wiring between relay and A/F sensor, and between A/F sensor and ECM. See WIRING DIAGRAMS article. Repair as necessary.