I replaced the ECM module because the old one had all "not ready" readings on the Tect 2 and failed the state emmissions testing. The new ECM module after 4 days had 3 of the 5 sensors working on the Tect 2. Cat Converter & Heated O2 sensor hadn't had enough combined cycle time to register. 10 days later the new ECM is not reading any codes again. Battery was not disconnected. Any ideas why the ECM is not reading the Emmissions sensors???
ECM Fails to register Emission Reading on 1996 Chevrolet Blazer
Once the emission monitors have run they should not reset unless codes are cleared or battery power is lost to the pcm. There is a difference between monitors and fault codes. Are you saying that all the monitors reset to not ready after 10 days? Are any fault codes pending or current?