Thanks for your response. I tested the pinkish/red wire and the white and got nothing. Neither were hot. Could be my testing equiptment or a bad ground. Not sure. So with all of the things I had done so far such as smoking the system, bench testing and finally changing the evap vent solinoid, disconnecting and taking out the MAF and spraying it will MAF cleaner, replace the blown 10amp fuse for ENG1 etc I had 4 codes. 3 emmissions and the MAF one as intermittent. So I was going to reset all of those codes and drive around. B4 I could manually do that my car did that. I showed no codes, 3 incomplete monitors and no ck engine light. I have done 5 reset drive cycles, hope I did those correctly. I now hv 2 incompletes..emissions and catalyst and no ck engine light. I expect the emmissions to complete first and can only hope no ck engine line comes on...then I can at least get the inspection done...pass and move on from there. I will let you know how that goes. Thanks for all of the help and guidance. Hv a gr8 day.

 

The ck engine light just came on in my Blazer. The interesting thing is this time the catalyst monitor


completed 1st...the Evap monitor is still incomplete. Here is the code. There is only one so far. What r ur thoughts? What is the cause for this code?

 

P0420 means that the post-cat O2 sensor is reading the same frequency of cycling as the pre-cat O2 sensor. Typically that means the cat converter is not retaining any oxygen (is not functioning) and needs replacement.

Imagine the green trace (below) cycling with the red trace. This plot of normal operation captured using Torque Pro for Android during a time period of about 5 seconds at 2000 rpm in park. Contrary to popular belief, pre-cat O2 sensors always actually cycle when they are controlling fuel mix. Exceptions are too lean, too rich, hard acceleration, or open loop when first started. For the pre-cat O2 sensors, as long as cycling crosses 0.45 volt, the fuel mix is being controlled.