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 between terminal No. 28 at ECM connector E10 and terminals No. 5 (Yellow wire) and No. 6 (Blue wire) at ECM harness connector E8. See Figure. Voltage should be 9-14 volts. If voltage is as specified, replace ECM. If voltage is not as specified, go to next step.
- Turn ignition off. Disconnect heated oxygen sensor No. 2 harness connector. Connector is located on front right side of engine. Measure resistance between terminals HT at bank No. 2 (Yellow wire) or bank No. 1 (Blue wire) and B+ (Black/Yellow wire) at heated oxygen sensor connector (component side). Resistance should be 11-16 ohms at 68°F (20°C). If resistance is not as specified, replace heated oxygen sensor No. 2. If resistance is as specified, go to next step.
- Disconnect oxygen sensor connector. Disconnect ECM E8 connector. Check for open circuit between terminals HT (Yellow or Blue wire) of oxygen sensor connector and HT1B (Blue wire) and HT2B (Yellow wire) of ECM E8 connector. Resistance should be one ohm or less. Check for short circuit between HT1B (Blue wire) and HT2B (Yellow wire) of ECM E8 connector and E2 (Brown wire) at ECM connector E10. See Figure. Resistance should be one megohm or more. If resistances are to specification, go to next step. If resistances are not to specification, repair or replace harness and connector.
- Disconnect negative battery terminal. Disconnect oxygen sensor connector. Check for open circuit between terminal No. 5 of computer relay side connector and +B (Black/White wire) at oxygen sensor connector. Do not insert tester leads hard or holder may be damaged. If resistance is one ohm or less, check ECM power source circuit. If resistance is greater than one ohm, repair or replace harness and connector.