The ECM monitors switching frequency ratio of front and rear HO2S. A 3-way catalyst with high oxygen storage capacity indicates low switching frequency of rear HO2S. As oxygen storage capacity decreases, rear HO2S switching frequency increases.
ECM then measures switching lag time between front and rear HO2S. Longer lag time indicates greater oxygen storage capacity. If lag time is within specified range, defective 3-way catalyst is indicated.
- Start engine and warm to operating temperature. Attach positive probe of voltmeter to ECM connector terminal No. 46 (front 02S) and negative probe to terminal No. 43 (engine ground). (Scheme 34) Raise engine speed to at least 2000 RPM and record voltage switching frequency. If voltage does not switch at least 5 times in 10 seconds, go to «DTC P0130»(ref-17825-S10256238792000122900000) - FRONT OXYGEN SENSOR (O2S). If voltage switches as specified, go to next step.
- Attach positive probe of voltmeter to ECM connector terminal No. 52 (rear H02S) and negative probe to terminal No. 43. Raise engine speed to at least 2000 RPM and record voltage switching frequency. Compare switching frequency with switching frequency obtained in step 1). Front O2S switching frequency should be about twice the switching frequency of rear HO2S. If switching frequency is not as specified, replace 3-way catalyst. If switching frequency is okay, go to next step.
- Visually inspect exhaust system for damage/leak and repair if necessary. Relieve fuel pressure and remove injector assembly. See the «REMOVE/INSTALL/OVERHAUL»(ref-17884) article. Do not remove fuel hose/injector from injector gallery. Disconnect CMP harness connector. Turn ignition on. Verify fuel does not drip from injector(s). Replace any injector(s) that drip fuel. Perform «FINAL CHECK»(ref-17825-S20538276422000122900000).
