Couple days ago I changed my A/F ratio sensor as it was bad, and reset the ECU. After that I had EVAP, Catalytic and O2 sensor monitor incomplete. Finally only had EVAP incomplete. I know EVAP takes time to complete.

But today when I went to start the car all three incomplete came back. EVAP, O2 and Catalytic.

I have perfect reading on O2 which is about 0.5-0.7. I would like to know if anyone knows what causing my ecu to reset by itself or why the ECU not storing the data.

 

A reset is going to cause all the cars systems to go through a self check process. Some items take more time to reset then others.

In the future just change the part and determine if the computer resets the trouble code on its own. If not then use an ODBII tool to reset only the code for the problem part.

 

Thanks for the reply. Eventually everthing was ready and complete, EVAP incomplete took the longest time to complete.

I bought one memory saver , from now on if I disconnect the battery to work on my car, I would use the memory saver tool so that I do not lose all the saved in fo and go through all these cycles again.