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Re: check engine light on in 97 wrangler YJ with error code reading 72
"bllsht" <nospam@dot.net> wrote in message news:nigrq2h2vlm58ducoftq5of5rvi6khcsp9@4ax.com... > On Tue, 16 Jan 2007 20:03:42 GMT, "Jeff Strickland" > <crwlr@verizon.net> wrote: > >> >>"bllsht" <nospam@dot.net> wrote in message >>news:567mq2lcmmf2td23fj2mo0bsfndgffg805@4ax.com. .. >>> On Sun, 14 Jan 2007 14:41:18 -0600, "DougW" >>> <post.replies@invalid.address> wrote: >>> >>>>bspear78 wrote: >>>>> I have a check engine light on, and the code is reading a 12 and a 72. >>>>> I know what the 12 means, but could not find any explanation for a >>>>> reading of 72. Anyone know what this means? >>>> >>>>72 Catalyst efficiency below required level. (Same as code 64) >>>> >>>>This means one of two things. >>>>1) your catalytic converter is plugging/cracking/failing >>>>2) the O2 sensor behind the cat is failing >>> >>> If the downstream O2 was failing you'd get a downstream O2 fault, not >>> a cat efficiency fault. >>> >> >>I'm not sure that is true in an OBD I car. The CAT is not a likely source >>of >>problems, and my money is on the after-CAT sensor going bad. > > An OBD I jeep wouldn't even have a downstream O2 sensor. You just lost > your money. > >> >>I am pretty sure that the downstream sensor can give an error that says >>the >>CAT is failing. This can happen because the system doesn't know that the >>sensor is bad, it only knows that the input from the sensor is not >>correct. >>The sensor can fail in a mode that makes the system say that the CAT is >>not >>working when the reality is that the sensor itself has taken a bye. > > Wrong. A failed downstream sensor will not set a cat efficiency fault. > In fact, the poorer the downstream sensor functions, the less likely a > cat fault would result. > >> >>Having said all of that, the OP says he has a 97 YJ. In the 97, it was >>called a TJ, and in 97, the codes are OBD II. > > A 1997 vehicle would be OBD II, no matter what it was called, or who > made it. > Well, then we're all chasing our shadows. Because, an OBD II car won't have a Code 72 ... >> >> >> >> >> |
Re: check engine light on in 97 wrangler YJ with error code reading 72
Jeff Strickland wrote:
> but, the upstream sensor will report a problem with the exhaust stream > before it enters the CAT, it will not cause the downstream sensor to > report that the CAT has failed. > > I suppose the downstream _could_ report a failed CAT, but my instinct > and expereince say that the upstream sensor will report its own > problem before the downstream sensor will report a bad CAT. It could be a cascade type problem. Going off my own experience with the ZJs only O2 sensor failing (but never setting codes). I first see it as a 2mpg drop in economy and then as black soot at the exhaust. A new O2 sensor fixes everything for the next five or so years. Newer compooters may well be better at detecting a marginal sensor. If the upstream sensor is off and allows the engine to run rich then the cat will be overburdened and the downstream will detect this as a loss of efficency. Replace the upstream, the engine then runs stoich, the cat can deal, and the downstream is back to happy again. -- DougW |
Re: check engine light on in 97 wrangler YJ with error code reading 72
Jeff Strickland wrote:
> but, the upstream sensor will report a problem with the exhaust stream > before it enters the CAT, it will not cause the downstream sensor to > report that the CAT has failed. > > I suppose the downstream _could_ report a failed CAT, but my instinct > and expereince say that the upstream sensor will report its own > problem before the downstream sensor will report a bad CAT. It could be a cascade type problem. Going off my own experience with the ZJs only O2 sensor failing (but never setting codes). I first see it as a 2mpg drop in economy and then as black soot at the exhaust. A new O2 sensor fixes everything for the next five or so years. Newer compooters may well be better at detecting a marginal sensor. If the upstream sensor is off and allows the engine to run rich then the cat will be overburdened and the downstream will detect this as a loss of efficency. Replace the upstream, the engine then runs stoich, the cat can deal, and the downstream is back to happy again. -- DougW |
Re: check engine light on in 97 wrangler YJ with error code reading 72
Jeff Strickland wrote:
> but, the upstream sensor will report a problem with the exhaust stream > before it enters the CAT, it will not cause the downstream sensor to > report that the CAT has failed. > > I suppose the downstream _could_ report a failed CAT, but my instinct > and expereince say that the upstream sensor will report its own > problem before the downstream sensor will report a bad CAT. It could be a cascade type problem. Going off my own experience with the ZJs only O2 sensor failing (but never setting codes). I first see it as a 2mpg drop in economy and then as black soot at the exhaust. A new O2 sensor fixes everything for the next five or so years. Newer compooters may well be better at detecting a marginal sensor. If the upstream sensor is off and allows the engine to run rich then the cat will be overburdened and the downstream will detect this as a loss of efficency. Replace the upstream, the engine then runs stoich, the cat can deal, and the downstream is back to happy again. -- DougW |
Re: check engine light on in 97 wrangler YJ with error code reading 72
Jeff Strickland wrote:
> but, the upstream sensor will report a problem with the exhaust stream > before it enters the CAT, it will not cause the downstream sensor to > report that the CAT has failed. > > I suppose the downstream _could_ report a failed CAT, but my instinct > and expereince say that the upstream sensor will report its own > problem before the downstream sensor will report a bad CAT. It could be a cascade type problem. Going off my own experience with the ZJs only O2 sensor failing (but never setting codes). I first see it as a 2mpg drop in economy and then as black soot at the exhaust. A new O2 sensor fixes everything for the next five or so years. Newer compooters may well be better at detecting a marginal sensor. If the upstream sensor is off and allows the engine to run rich then the cat will be overburdened and the downstream will detect this as a loss of efficency. Replace the upstream, the engine then runs stoich, the cat can deal, and the downstream is back to happy again. -- DougW |
Re: check engine light on in 97 wrangler YJ with error code reading 72
On Thu, 18 Jan 2007 19:01:19 GMT, "Jeff Strickland"
<crwlr@verizon.net> wrote: > >"bllsht" <nospam@dot.net> wrote in message >news:nigrq2h2vlm58ducoftq5of5rvi6khcsp9@4ax.com.. . >> On Tue, 16 Jan 2007 20:03:42 GMT, "Jeff Strickland" >> <crwlr@verizon.net> wrote: >> >>> >>>"bllsht" <nospam@dot.net> wrote in message >>>news:567mq2lcmmf2td23fj2mo0bsfndgffg805@4ax.com ... >>>> On Sun, 14 Jan 2007 14:41:18 -0600, "DougW" >>>> <post.replies@invalid.address> wrote: >>>> >>>>>bspear78 wrote: >>>>>> I have a check engine light on, and the code is reading a 12 and a 72. >>>>>> I know what the 12 means, but could not find any explanation for a >>>>>> reading of 72. Anyone know what this means? >>>>> >>>>>72 Catalyst efficiency below required level. (Same as code 64) >>>>> >>>>>This means one of two things. >>>>>1) your catalytic converter is plugging/cracking/failing >>>>>2) the O2 sensor behind the cat is failing >>>> >>>> If the downstream O2 was failing you'd get a downstream O2 fault, not >>>> a cat efficiency fault. >>>> >>> >>>I'm not sure that is true in an OBD I car. The CAT is not a likely source >>>of >>>problems, and my money is on the after-CAT sensor going bad. >> >> An OBD I jeep wouldn't even have a downstream O2 sensor. You just lost >> your money. >> >>> >>>I am pretty sure that the downstream sensor can give an error that says >>>the >>>CAT is failing. This can happen because the system doesn't know that the >>>sensor is bad, it only knows that the input from the sensor is not >>>correct. >>>The sensor can fail in a mode that makes the system say that the CAT is >>>not >>>working when the reality is that the sensor itself has taken a bye. >> >> Wrong. A failed downstream sensor will not set a cat efficiency fault. >> In fact, the poorer the downstream sensor functions, the less likely a >> cat fault would result. >> >>> >>>Having said all of that, the OP says he has a 97 YJ. In the 97, it was >>>called a TJ, and in 97, the codes are OBD II. >> >> A 1997 vehicle would be OBD II, no matter what it was called, or who >> made it. >> > >Well, then we're all chasing our shadows. Because, an OBD II car won't have >a Code 72 ... Oh really? Please tell us how you came to that conclusion. > > > > > >>> >>> >>> >>> >>> |
Re: check engine light on in 97 wrangler YJ with error code reading 72
On Thu, 18 Jan 2007 19:01:19 GMT, "Jeff Strickland"
<crwlr@verizon.net> wrote: > >"bllsht" <nospam@dot.net> wrote in message >news:nigrq2h2vlm58ducoftq5of5rvi6khcsp9@4ax.com.. . >> On Tue, 16 Jan 2007 20:03:42 GMT, "Jeff Strickland" >> <crwlr@verizon.net> wrote: >> >>> >>>"bllsht" <nospam@dot.net> wrote in message >>>news:567mq2lcmmf2td23fj2mo0bsfndgffg805@4ax.com ... >>>> On Sun, 14 Jan 2007 14:41:18 -0600, "DougW" >>>> <post.replies@invalid.address> wrote: >>>> >>>>>bspear78 wrote: >>>>>> I have a check engine light on, and the code is reading a 12 and a 72. >>>>>> I know what the 12 means, but could not find any explanation for a >>>>>> reading of 72. Anyone know what this means? >>>>> >>>>>72 Catalyst efficiency below required level. (Same as code 64) >>>>> >>>>>This means one of two things. >>>>>1) your catalytic converter is plugging/cracking/failing >>>>>2) the O2 sensor behind the cat is failing >>>> >>>> If the downstream O2 was failing you'd get a downstream O2 fault, not >>>> a cat efficiency fault. >>>> >>> >>>I'm not sure that is true in an OBD I car. The CAT is not a likely source >>>of >>>problems, and my money is on the after-CAT sensor going bad. >> >> An OBD I jeep wouldn't even have a downstream O2 sensor. You just lost >> your money. >> >>> >>>I am pretty sure that the downstream sensor can give an error that says >>>the >>>CAT is failing. This can happen because the system doesn't know that the >>>sensor is bad, it only knows that the input from the sensor is not >>>correct. >>>The sensor can fail in a mode that makes the system say that the CAT is >>>not >>>working when the reality is that the sensor itself has taken a bye. >> >> Wrong. A failed downstream sensor will not set a cat efficiency fault. >> In fact, the poorer the downstream sensor functions, the less likely a >> cat fault would result. >> >>> >>>Having said all of that, the OP says he has a 97 YJ. In the 97, it was >>>called a TJ, and in 97, the codes are OBD II. >> >> A 1997 vehicle would be OBD II, no matter what it was called, or who >> made it. >> > >Well, then we're all chasing our shadows. Because, an OBD II car won't have >a Code 72 ... Oh really? Please tell us how you came to that conclusion. > > > > > >>> >>> >>> >>> >>> |
Re: check engine light on in 97 wrangler YJ with error code reading 72
On Thu, 18 Jan 2007 19:01:19 GMT, "Jeff Strickland"
<crwlr@verizon.net> wrote: > >"bllsht" <nospam@dot.net> wrote in message >news:nigrq2h2vlm58ducoftq5of5rvi6khcsp9@4ax.com.. . >> On Tue, 16 Jan 2007 20:03:42 GMT, "Jeff Strickland" >> <crwlr@verizon.net> wrote: >> >>> >>>"bllsht" <nospam@dot.net> wrote in message >>>news:567mq2lcmmf2td23fj2mo0bsfndgffg805@4ax.com ... >>>> On Sun, 14 Jan 2007 14:41:18 -0600, "DougW" >>>> <post.replies@invalid.address> wrote: >>>> >>>>>bspear78 wrote: >>>>>> I have a check engine light on, and the code is reading a 12 and a 72. >>>>>> I know what the 12 means, but could not find any explanation for a >>>>>> reading of 72. Anyone know what this means? >>>>> >>>>>72 Catalyst efficiency below required level. (Same as code 64) >>>>> >>>>>This means one of two things. >>>>>1) your catalytic converter is plugging/cracking/failing >>>>>2) the O2 sensor behind the cat is failing >>>> >>>> If the downstream O2 was failing you'd get a downstream O2 fault, not >>>> a cat efficiency fault. >>>> >>> >>>I'm not sure that is true in an OBD I car. The CAT is not a likely source >>>of >>>problems, and my money is on the after-CAT sensor going bad. >> >> An OBD I jeep wouldn't even have a downstream O2 sensor. You just lost >> your money. >> >>> >>>I am pretty sure that the downstream sensor can give an error that says >>>the >>>CAT is failing. This can happen because the system doesn't know that the >>>sensor is bad, it only knows that the input from the sensor is not >>>correct. >>>The sensor can fail in a mode that makes the system say that the CAT is >>>not >>>working when the reality is that the sensor itself has taken a bye. >> >> Wrong. A failed downstream sensor will not set a cat efficiency fault. >> In fact, the poorer the downstream sensor functions, the less likely a >> cat fault would result. >> >>> >>>Having said all of that, the OP says he has a 97 YJ. In the 97, it was >>>called a TJ, and in 97, the codes are OBD II. >> >> A 1997 vehicle would be OBD II, no matter what it was called, or who >> made it. >> > >Well, then we're all chasing our shadows. Because, an OBD II car won't have >a Code 72 ... Oh really? Please tell us how you came to that conclusion. > > > > > >>> >>> >>> >>> >>> |
Re: check engine light on in 97 wrangler YJ with error code reading 72
On Thu, 18 Jan 2007 19:01:19 GMT, "Jeff Strickland"
<crwlr@verizon.net> wrote: > >"bllsht" <nospam@dot.net> wrote in message >news:nigrq2h2vlm58ducoftq5of5rvi6khcsp9@4ax.com.. . >> On Tue, 16 Jan 2007 20:03:42 GMT, "Jeff Strickland" >> <crwlr@verizon.net> wrote: >> >>> >>>"bllsht" <nospam@dot.net> wrote in message >>>news:567mq2lcmmf2td23fj2mo0bsfndgffg805@4ax.com ... >>>> On Sun, 14 Jan 2007 14:41:18 -0600, "DougW" >>>> <post.replies@invalid.address> wrote: >>>> >>>>>bspear78 wrote: >>>>>> I have a check engine light on, and the code is reading a 12 and a 72. >>>>>> I know what the 12 means, but could not find any explanation for a >>>>>> reading of 72. Anyone know what this means? >>>>> >>>>>72 Catalyst efficiency below required level. (Same as code 64) >>>>> >>>>>This means one of two things. >>>>>1) your catalytic converter is plugging/cracking/failing >>>>>2) the O2 sensor behind the cat is failing >>>> >>>> If the downstream O2 was failing you'd get a downstream O2 fault, not >>>> a cat efficiency fault. >>>> >>> >>>I'm not sure that is true in an OBD I car. The CAT is not a likely source >>>of >>>problems, and my money is on the after-CAT sensor going bad. >> >> An OBD I jeep wouldn't even have a downstream O2 sensor. You just lost >> your money. >> >>> >>>I am pretty sure that the downstream sensor can give an error that says >>>the >>>CAT is failing. This can happen because the system doesn't know that the >>>sensor is bad, it only knows that the input from the sensor is not >>>correct. >>>The sensor can fail in a mode that makes the system say that the CAT is >>>not >>>working when the reality is that the sensor itself has taken a bye. >> >> Wrong. A failed downstream sensor will not set a cat efficiency fault. >> In fact, the poorer the downstream sensor functions, the less likely a >> cat fault would result. >> >>> >>>Having said all of that, the OP says he has a 97 YJ. In the 97, it was >>>called a TJ, and in 97, the codes are OBD II. >> >> A 1997 vehicle would be OBD II, no matter what it was called, or who >> made it. >> > >Well, then we're all chasing our shadows. Because, an OBD II car won't have >a Code 72 ... Oh really? Please tell us how you came to that conclusion. > > > > > >>> >>> >>> >>> >>> |
Re: check engine light on in 97 wrangler YJ with error code reading 72
On Thu, 18 Jan 2007 18:41:15 GMT, "Jeff Strickland"
<crwlr@verizon.net> wrote: > >"DougW" <post.replies@invalid.address> wrote in message >news:d8drh.41182$oA1.30083@newsfe19.lga... >> Jeff Strickland wrote: >>> "bllsht" wrote ... >>>> "DougW" wrote: >>>> >>>>> bspear78 wrote: >>>>>> I have a check engine light on, and the code is reading a 12 and a >>>>>> 72. I know what the 12 means, but could not find any explanation >>>>>> for a reading of 72. Anyone know what this means? >>>>> >>>>> 72 Catalyst efficiency below required level. (Same as code 64) >>>>> >>>>> This means one of two things. >>>>> 1) your catalytic converter is plugging/cracking/failing >>>>> 2) the O2 sensor behind the cat is failing >>>> >>>> If the downstream O2 was failing you'd get a downstream O2 fault, not >>>> a cat efficiency fault. >>>> >>> >>> I'm not sure that is true in an OBD I car. The CAT is not a likely >>> source of problems, and my money is on the after-CAT sensor going bad. >>> >>> I am pretty sure that the downstream sensor can give an error that >>> says the CAT is failing. This can happen because the system doesn't >>> know that the sensor is bad, it only knows that the input from the >>> sensor is not correct. The sensor can fail in a mode that makes the >>> system say that the CAT is not working when the reality is that the >>> sensor itself has taken a bye. >>> Having said all of that, the OP says he has a 97 YJ. In the 97, it was >>> called a TJ, and in 97, the codes are OBD II. >> >> I've seen O2 sensors go bad, but not bad enough to set a fault. Usually >> it's the forward one and the only thing it does is give you bad milage >> and black exhaust. Figured the rearward one could go equally bad and >> throw a code even if the cat was good. >> > > >I agree, usually it's the front sensor. But, the CAT's condition is not >checked at the front, it's checked at the back. > >The "front" (upstream) sensor will adjust the fuel mix as much as it can, >and eventually throw a code that results from detecting an out of range >condition (rich or lean mixture) that the computer is not able to adjust >fuel delivery to correct for. The out of range can be true or false. If >true, the cause can be related to stuff associated with fuel delivery -- >faulty injectors, that sort of thing -- but if false, then the trouble is a >faulty sensor. > >The "back" (downstream) sensor is looking at what comes out of the CAT. It >can also give a true or false report. If the report is true, the cause is a >faulty CAT, but if false, the cause is a faulty sensor. Given the >environment (hot exhaust stream), I tend to look at faulty sensors, >especially when the CAT is reported as the trouble. The CAT itself is very >robust, and is capable of lasting nearly as long as the vehicle it is >mounted to. The sensor is not so robust. > >If the code says that the CAT is below efficiency, I'd be thinking the >sensor that reports the CAT is what is really below efficiency. If the >problem was happening at the upstream sensor, the report would not be that >the CAT is bad, because such data would be collected before the CAT comes >into play. A report from the upstream sensor would include information that >the fuel mixture was 1.) too rich, 2.) too lean, or 3.) out of range, >without an indication as to the content of the mixture. The downstream >sensor does not know about to rich or too lean, it only knows that what >comes out of the CAT has not been cleaned up, relative to what went in. The >upstream sensor knows what goes into the CAT, the downstream sensor knows >what comes out. > > > You're both leaping to conclusions without even having a clue as to how the PCM determines the cat converter's efficiency. |
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