pending DTC code on OBD II

Hi,
I purchased an OBD II scanner, and read a DTC(P0420). When I am reading
the OBD manual, I don't know what is "pending code", and when and why
it is there(under what condition it generates a pending code?)? I have
cleared the DTC, but manual mentions that OBD 2 Drive cycle must be
performed before resetting all the monitors, what is "OBD 2 Drive
cycle"? If I just drive my car after clearing DTC, will the car do "OBD
2 Drive cycle" automatically?
Thanks.
WM

[email]wenmang@yahoo.com[/email] wrote in
news:1130347972.913247.290340@g14g2000cwa.googlegroups.com:
[color=blue]
> Hi,
> I purchased an OBD II scanner, and read a DTC(P0420). When I am reading
> the OBD manual, I don't know what is "pending code", and when and why
> it is there(under what condition it generates a pending code?)? I have
> cleared the DTC, but manual mentions that OBD 2 Drive cycle must be
> performed before resetting all the monitors, what is "OBD 2 Drive
> cycle"? If I just drive my car after clearing DTC, will the car do "OBD
> 2 Drive cycle" automatically?[/color]


Go ye to the source:
[url]http://www.obdii.com/[/url]

The answers you seek all are there.

--
TeGGeR®

The website doesn't have search functionality, I found info about
"drive cycle", but I cannot find about "generating pending code".
Hopefully, this can be answered here. Thanks.

<wenmang@yahoo.com> wrote in message
news:1130351980.782982.255380@g49g2000cwa.googlegroups.com...[color=blue]
> The website doesn't have search functionality, I found info about
> "drive cycle", but I cannot find about "generating pending code".
> Hopefully, this can be answered here. Thanks.[/color]


Diagnostic Trouble Code ("DTC") P0420 means that the catalyst system
efficiency for Bank 1 is operating below threshold.

In plain English, it means that the system thinks that the exhaust coming
out of the catalytic converter is not clean enough. There are 2 possible
causes for this trouble code: 1) the catalytic converter is not cleaning up
the exhaust or 2) the O2 sensor that monitors the exhaust coming out of the
catalytic converter is not measuring properly. My guess is that reason #2
is a more likely cause - the O2 sensor has gradually lost its effectiveness
but is still sending a signal so the OBD system does not give an O2 sensor
trouble code.

If you car is still covered by the emissions warranty (check your warranty
booklet) then if the light comes on again, do not clear the code yourself.
Let the code remain in memory and take it to a dealer for an emissions
warranty repair.
--
Ray O
correct the return address punctuation to reply

Thanks Ray. I asked about P0420 before. I just want to understand why
OBD II manual indicates that how OBD II scanner can detect a pending
DTC and what does it mean? like potential problem on the way if it
presents or some kind of alert functionality.
Thanks.

Got answer from manufacture, thanks.
"The tool will display pending codes. A pending code is a problem that
the vehicle's computer has seen, but has not seen it enough to consider
it a priority and turn on the MIL. "

<wenmang@yahoo.com> wrote in message
news:1130353018.188342.325610@o13g2000cwo.googlegroups.com...[color=blue]
> Thanks Ray. I asked about P0420 before. I just want to understand why
> OBD II manual indicates that how OBD II scanner can detect a pending
> DTC and what does it mean? like potential problem on the way if it
> presents or some kind of alert functionality.
> Thanks.
>[/color]

The OBD II system does not detect or predict pending problems. It can only
detect the presence or absence of problems.

To reduce false alarms, some problems need to be detected over the course of
several trips before the check engine light (formally called a malfunction
indicator light, or MIL) is illuminated and needs to not detect the problem
of the course of several trips to extinguish the MIL. Toyota calls this 2
trip detection logic, and there are certain things that have to happen to
count for a trip, like starting the engine cold, driving a certain number of
miles over a certain speed, and engine coolant and O2 sensors reaching a
certain temperature, so backing the car out of your garage will not be
counted as a trip.

I don't know what brand scanner you have, but I'm guessing that the scanner
manufacturer did not have a complete list of DTC's when they printed the
manual, so if they didn't have the explanation of the codes, they were
listed as pending DTC.

A certain number of OBD II diagnostic trouble codes are universal for all
vehicles sold in North America (perhaps the world). You can use this site
[url]http://www.obdii.com/codes.html[/url] for a more complete list of codes.

Some OBD II trouble codes are specific to certain brands and would not be
listed on the site a pasted above.

--
Ray O
correct the return address punctuation to reply

<wenmang@yahoo.com> wrote in message
news:1130353421.957434.77940@g43g2000cwa.googlegroups.com...[color=blue]
> Got answer from manufacture, thanks.
> "The tool will display pending codes. A pending code is a problem that
> the vehicle's computer has seen, but has not seen it enough to consider
> it a priority and turn on the MIL. "
>[/color]
I learned something new today!
--
Ray O
correct the return address punctuation to reply

After reading your post, I am confused. I purchased Innova's OBD II
scanner from walmart store. Here is their
website:[url]http://www.canobd2.com[/url]
The device has three light indicators, green, yellow and red. In the
user manual, there is a short description about "yellow LED"
? Yellow LED - indicates there is a possible problem. A "Pending" DTC
is present and/or some of the vehicle's emission monitors have not run
their diagnostic testing.

That is why I am aksing when the yellow LED is on, what does it mean?

<wenmang@yahoo.com> wrote in message
news:1130357971.112035.228880@g14g2000cwa.googlegroups.com...[color=blue]
> After reading your post, I am confused. I purchased Innova's OBD II
> scanner from walmart store. Here is their
> website:[url]http://www.canobd2.com[/url]
> The device has three light indicators, green, yellow and red. In the
> user manual, there is a short description about "yellow LED"
> ? Yellow LED - indicates there is a possible problem. A "Pending" DTC
> is present and/or some of the vehicle's emission monitors have not run
> their diagnostic testing.
>[/color]

Wow! You spent $249 for a Scan tool? It is a nice tool with freeze frame
capabilities but if you are not going to interpret actual sensor data output
or if you automotive knowledge is limited, you can get away with a basic
tool for under $100. For example, if you get voltage and cycle data from
the #2 O2 sensor, would you know if the data indicates a good or a bad
sensor?

Your explanation about the purpose of the yellow LED is different from the
one I found on the site you referred to.
[url]http://www.canobd2.com/tool/quick_diagnose.asp[/url] On this page, it says that
the yellow LED means possible problem / not ready for emissions test. The
reason a vehicle might not be ready for an emissions test is that the system
has not warmed up enough to go into "closed loop" mode. If you take the car
for a 15 minute ride and then plug in the code reader, I'll bet you get a
red light instead of a yellow light.

I suppose it is possible for a scan tool to detect a problem with 2-trip
detection logic - that is, it found a problem with the first trip and is
waiting for the second trip but in that scenario, the MIL would not be lit
yet so you would not normally have a reason to pull codes.

Don't worry so much about the LED colors and focus on the actual code.
--
Ray O
correct the return address punctuation to reply

Thanks Ray. Actually I spent $69 on OBD 2, they have two models, the
other one costs $100 at walmart. They are not the one advertised on
their website.

<wenmang@yahoo.com> wrote in message
news:1130360043.398034.207880@z14g2000cwz.googlegroups.com...[color=blue]
> Thanks Ray. Actually I spent $69 on OBD 2, they have two models, the
> other one costs $100 at walmart. They are not the one advertised on
> their website.
>[/color]

You're welcome!

IMO, most people should not buy more than a simple code reader unless they
have a factory repair manual and know how to interpret actual sensor output
readings.
--
Ray O
correct the return address punctuation to reply

"Ray O" <rokigawa@tristarassociatesDOT.com> wrote:
[color=blue]
>
><wenmang@yahoo.com> wrote in message
>news:1130353018.188342.325610@o13g2000cwo.googlegroups.com...[color=green]
>> Thanks Ray. I asked about P0420 before. I just want to understand why
>> OBD II manual indicates that how OBD II scanner can detect a pending
>> DTC and what does it mean? like potential problem on the way if it
>> presents or some kind of alert functionality.
>> Thanks.
>>[/color]
>
>The OBD II system does not detect or predict pending problems. It can only
>detect the presence or absence of problems.
>
>To reduce false alarms, some problems need to be detected over the course of
>several trips before the check engine light (formally called a malfunction
>indicator light, or MIL) is illuminated and needs to not detect the problem
>of the course of several trips to extinguish the MIL. Toyota calls this 2
>trip detection logic,[/color]

snip

But Ray, isn't that the same thing as predicting?...if it saw the
same error several times in a row then it'll turn on the MIL,
right?...so if it saw the same error maybe twice, then no error
for another several trips then three more in a row...see my
point?...isn't it 'predicting' a problem (sort of?)
--

-Gord.
(use gordon in email)

"Gord Beaman" <gord@islandtelecom.com> wrote in message
news:pd80m1h3cc1aep9duuqbvbus1elk7cqgan@4ax.com...[color=blue]
> "Ray O" <rokigawa@tristarassociatesDOT.com> wrote:
>[color=green]
>>
>><wenmang@yahoo.com> wrote in message
>>news:1130353018.188342.325610@o13g2000cwo.googlegroups.com...[color=darkred]
>>> Thanks Ray. I asked about P0420 before. I just want to understand why
>>> OBD II manual indicates that how OBD II scanner can detect a pending
>>> DTC and what does it mean? like potential problem on the way if it
>>> presents or some kind of alert functionality.
>>> Thanks.
>>>[/color]
>>
>>The OBD II system does not detect or predict pending problems. It can
>>only
>>detect the presence or absence of problems.
>>
>>To reduce false alarms, some problems need to be detected over the course
>>of
>>several trips before the check engine light (formally called a malfunction
>>indicator light, or MIL) is illuminated and needs to not detect the
>>problem
>>of the course of several trips to extinguish the MIL. Toyota calls this 2
>>trip detection logic,[/color]
>
> snip
>
> But Ray, isn't that the same thing as predicting?...if it saw the
> same error several times in a row then it'll turn on the MIL,
> right?...so if it saw the same error maybe twice, then no error
> for another several trips then three more in a row...see my
> point?...isn't it 'predicting' a problem (sort of?)
> --
>
> -Gord.
> (use gordon in email)[/color]

I guess it's a matter of semantics. I was thinking of "predicting" as
anticipating a problem before the problem actually occurs, and I was
thinking of the 2 trip detection logic as double-checking.

On trouble codes that have 2 trip detection logic, I guess you could
consider a problem with one trip, and the second trip has not occurred yet a
"prediction" but that assumes that the problem will definitely occur on
another trip. I gather that the OP's scan tool will illuminate a light
showing that the ECU has stored a trouble code for 1 trip but not another
trip yet so the MIL is not illuminated. The problem is, you normally would
not scan for codes unless the MIL comes on, so unless you drive around with
the scan tool connected, there is little benefit to "predicting" a trouble
code.
--
Ray O
correct the return address punctuation to reply