P0430 Chevy Express '97

billr

wrench
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When I started it up this evening, that last monitor turned "OK" before I got it out of the garage. I'm guessing the PCM could not check for the HTR efficiency until it had verified the O2 sensors were OK; by then it was too late to check the cold-start behavior of the heaters.

By the way, contrary to what has been suggested earlier here, these S2 sensors seem to cross 450 mV, not stay stuck in "rich" (> 450 mV); but cross at a slower rate than the S1 sensors.
 

nickb2

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but cross at a slower rate than the S1 sensors.
Although sometimes my writing sucks, this IS what your looking for.

Basically, if S2 sensors are switching slowly, that is a good sign. If they are stuck, end line fuel strategy is biased and S1 one sensors are the first responders here.

The S2 sensors are just there to rectify and verify if cats are doing their job.


From my understanding, put in laymans terms if you will, the front o2 sensors are there to correct fuel and adopt a short term strategy, long term is the job of the rear o2, then the algorythm goes into play, and once the system has completed a complete drive cycle, it can now determine if this is a cat problem or just a lean or rich problem.

Learning how to read all this in live data takes alot of experience. You should see some of the stuff I have to decipher sometimes.

Point of case, car comes in the other day. honda oddesy with a 3.5l

Misfire on multiple cylinders, car wont go past 20km per hr.

No cat codes, just one code indicating ecm want to lean out.

Took me a while to get to my diagnostic. But I pulled out my vacuum gauge, and bam, clogged cat or restricted exhaust.

What took me a while to digest that was, the fact that at idle, it didn't miss, and trims were good.

Then I took out my back pressure gauge, confirmed B1 cat was gone.

Took apart exhaust, found honeycomb in third cat. And yes, these where 3 way cat systems. Now they are even worse. Seeing 4 cat and now with DPF, 8 sensors to monitor diesel particulate.
 

nickb2

Wrench. Diagnostic Tech.
Joined
Nov 22, 2008
Messages
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Location
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I will try to find more scanner danner videos or some NGK video training guides. They are hugely informative. Sometimes the stuff I learn is real hard to put into words.

I must say this often. I live in a bi lingual world most of the time. SO being patient with me is a must as I have to digest very complex info and translate and then put all that back here into something that may only makes sense to me.

:(
 
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