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Once the readiness monitors are set, if you never do a drive cycle, is it possible for a DTC to be triggered?



 
 
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  #1  
Old November 19th 20, 01:08 AM posted to rec.autos.tech
Arlen Holder
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Posts: 40
Default Once the readiness monitors are set, if you never do a drive cycle, is it possible for a DTC to be triggered?

Curiosity question:

If you (a) fill the readiness monitors, and you have no code at that
moment, and then, if you (b) NEVER go through the steps of the Federal Test
Procedure Drive Cycle, is it even possible for a DTC to be triggered?

This is a strange question, which perhaps nobody knows the answer to,
but it suddenly came up today, where I had to make a quick judgment call.

Now I have time to _ask_ the question I had to make a quick decision on.
o Q: If you don't ever run a drive cycle, can you _not_ get a DTC?

1. I had been clearing a DTC as per a current thread described below:
o Request for diagnostic advice to pinpoint least expensive solution to resolve persistent P0421 OBDII DTC
<https://groups.google.com/g/rec.autos.tech/c/u3mtjAGgwK8>

2. That DTC came back under two specific circumstances:
a. Sometimes it came back the instant the CAT readiness monitor was set
b. But, other times, it took a day or two _after_ the CAT monitor set

3. This morning, when I visited the owner to run the "cold start" test,
I noticed the readiness registers were all set & there was no code.

So I instantly commanded the college-aged owner to get in the car with me,
while I drove to the nearest smog station within that "no code" window.

My dilemma?
o Should I run within the parameters of the drive cycle? Or not?

I didn't have time to think about the answer, so my "gut feeling" was to
ensure that I did NOT drive within the Federal Test Procedure drive cycle
parameters (e.g., I went over 60 on the highway, and under 20 on access
roads and I shut the engine off at light so as not to idle for any length
of time, etc.).

That is, I expressly avoided doing any part of the drive cycle, even though
I knew that the readiness monitors were all filled and there was no code.

Yet.

Certainly, at some point the DTC will come back (it always has); but the
question is more direct than that, and mostly out of sheer curiosity.

If you (a) fill the readiness monitors, and you have no code at that
moment, and then, if you (b) NEVER go through the steps of the Federal Test
Procedure Drive Cycle, is it even possible for a DTC to be triggered?
--
Note: These are unrealistic long-term conditions; but for a 10-mile drive,
they're not as unrealistic as they might at first appear to be.
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  #2  
Old November 21st 20, 07:21 AM posted to rec.autos.tech
Steve W.[_6_]
external usenet poster
 
Posts: 1,161
Default Once the readiness monitors are set, if you never do a drivecycle, is it possible for a DTC to be triggered?

Arlen Holder wrote:
> Curiosity question:
>
> If you (a) fill the readiness monitors, and you have no code at that
> moment, and then, if you (b) NEVER go through the steps of the Federal Test
> Procedure Drive Cycle, is it even possible for a DTC to be triggered?


Yes, the written drive cycle is simply the fastest way to set the
monitors, however those are not one time tests, they run in two modes,
some are continuous tests while others are very specific cycles. The
EVAP and warm up cat tests use more precise parameters but they still
run every time those conditions are met.
For instance many EVAP tests will not run on a system if the tank is
over 3/4 or under 1/4 full. It used to be common for vehicles with leaks
to show up with all the monitors set but the EVAP and surprise they had
a full tank of fuel and a 5 gallon can in the trunk to keep it full so
it wouldn't run the cycle!! A week after inspection the light was back on..


>
> This is a strange question, which perhaps nobody knows the answer to,
> but it suddenly came up today, where I had to make a quick judgment call.
>
> Now I have time to _ask_ the question I had to make a quick decision on.
> o Q: If you don't ever run a drive cycle, can you _not_ get a DTC?
>
> 1. I had been clearing a DTC as per a current thread described below:
> o Request for diagnostic advice to pinpoint least expensive solution to resolve persistent P0421 OBDII DTC
> <https://groups.google.com/g/rec.autos.tech/c/u3mtjAGgwK8>
>
> 2. That DTC came back under two specific circumstances:
> a. Sometimes it came back the instant the CAT readiness monitor was set
> b. But, other times, it took a day or two _after_ the CAT monitor set
>
> 3. This morning, when I visited the owner to run the "cold start" test,
> I noticed the readiness registers were all set & there was no code.
>
> So I instantly commanded the college-aged owner to get in the car with me,
> while I drove to the nearest smog station within that "no code" window.
>
> My dilemma?
> o Should I run within the parameters of the drive cycle? Or not?
>
> I didn't have time to think about the answer, so my "gut feeling" was to
> ensure that I did NOT drive within the Federal Test Procedure drive cycle
> parameters (e.g., I went over 60 on the highway, and under 20 on access
> roads and I shut the engine off at light so as not to idle for any length
> of time, etc.).
>
> That is, I expressly avoided doing any part of the drive cycle, even though
> I knew that the readiness monitors were all filled and there was no code.
>
> Yet.
>
> Certainly, at some point the DTC will come back (it always has); but the
> question is more direct than that, and mostly out of sheer curiosity.
>
> If you (a) fill the readiness monitors, and you have no code at that
> moment, and then, if you (b) NEVER go through the steps of the Federal Test
> Procedure Drive Cycle, is it even possible for a DTC to be triggered?


It isn't the federal test that triggers the codes, it is the vehicles
own testing. The federal cycle is only intended to verify that the
system works in the least amount of time.

--
Steve W.
 




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