XPost: alt.home.repair, ca.driving   
   From: arlen_holder@newmachines.com   
      
   On Wed, 18 Nov 2020 11:38:43 -0500, Steve W. wrote:   
      
   >> The keyword here is "warmup" (which only you caught in the initial post).   
   >>  "the Bank 1 Catalytic Converter isn't warming up sufficiently"   
   >>   
   >> This makes the problem harder to diagnose since, as you seem to have   
   >> realized instantly, it will only show up during the warmup process.   
   >   
   > In simple terms it means that the converter isn't starting to operate as   
   > fast as the table in the ECM thinks it should given the engines run   
   > time, fuel and air states.   
      
   Hi Steve W.,   
      
   Thanks for your advice, as cat "warmup" is the critical parameter for sure!   
      
   I agree that the P0421 indicates a catalytic "warmup" fault, where it must   
   be close since I've seen three situations occur multiple times so far:   
   o In most cases, the P0421 is set the instant readiness monitors are full   
   o In other cases, the P0421 is set days after readiness monitors are full   
   o Oddly, once set, it doesn't ever reset (e.g., after 3 good drive cycles)   
      
   > The ECM looks at the time the engine started, it's loading, coolant   
   > temp, air temp, rpm timing, injector flow, air flow and a couple other   
   > sensors and using the tables programmed in it has decided the converter   
   > isn't starting to do it's job fast enough based on the numbers they used   
   > in the programming.   
      
   Of course.   
   o The difficult question to answer is what to test to debug during warmup.   
      
   The lambda sensor is heated, so it only takes ~20 seconds to warm up.   
   o But what's expected warmup time for a cat (& how exactly is it measured?)   
      
   > Sometimes this can simply be a bar sensor, IE the rear sensor is   
   > sluggish due to contamination or age and the ECM thinks the cat is the   
   > issue when it's the sensor. That is the whole point of the graph, you   
   > want to see how long it takes on a cold start for the sensors to start   
   > working and what the voltage numbers are.   
      
   Yes. Indeed.   
      
   I certainly didn't realize this when I originally opened this thread, but I   
   do realize that measuring how long it takes to get to steady state after an   
   overnight rest & morning cold start seems to be a critical diagnostic.   
      
   > The direct testing at the   
   > sensor is also the best testing because everything that comes through a   
   > scan tool is processed data, it has been known to be wrong multiple   
   > times, while direct testing shows the raw data.   
      
   Understood. I'm very familiar with flying leads.   
   o I simply prefer not to do that to other people's cars if I don't have to.   
      
   What I need at the moment is to borrow the vehicle and see what I can   
   determine in the first crucial minute.   
   o I know it only takes about ~20 seconds for the sensors to warm up   
      
   But I'm not yet sure how to test the time it takes for the cat to warm up.   
   o Especially when it appears to be a borderline condition on this vehicle.   
   --   
   Diagnostics are useless if we don't first understand how the system works.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)