XPost: alt.home.repair, ca.driving   
   From: csr684@NOTyahoo.com   
      
   Arlen Holder wrote:   
   > 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)   
      
   It sounds like the issue is borderline, IE the cat isn't really dead but   
   under colder temps it takes longer to warm up and sets the code.   
      
   >   
   >> 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?)   
      
   The downstream sensor is the one used for this testing, the lambda   
   sensor upstream isn't really involved in the test other than to verify   
   that the mix going into the cat is correct.   
      
   >   
   >> 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.   
      
   Yep, Steady state isn't the real item it tests though, what the test   
   looks for is how long does the cat take to start working and lower the   
   levels going to the downstream sensor.   
      
   >   
   >> 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.   
      
   That is the trick in testing, the easiest way is to use a 5 gas analyzer   
   and watch the numbers as the cat ignites, but not everyone has one. The   
   next is to measure the sensor output directly and see when it actually   
   shows a change. Just remember that it only uses the downstream sensor   
   for this test.   
      
      
      
   --   
   Steve W.   
      
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