Persistent p0172 and p0175

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MBS1994

Well-Known Member
How are the readings? Do they seem to jive? It's possible that a different brand might use different wire colours to the connector. If in doubt, get a new one for your year and model.
It's a gm sensor I pulled it off a unknown v8 in the junk yard. They do seem to match well, I'm going to buy a new one today and spark plug.
 

TJBaker57

Well-Known Member
Wouldn't the live data be coming from the sensor or how does it calculate it?

That's the point... I think. Or did I miss something? Were you questioning if the sensor was OK to use? If the value returned by the sensor is correct, does it matter what type of connector it uses?
 
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MBS1994

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That's the point... I think. Or did I miss something? Were you questioning if the sensor was OK to use? If the value returned by the sensor is correct, does it matter what type of connector it uses?
No maybe I'm overthinking it because I've had to much spare time on my hands. I'm going to replace the spark plug and coil pack and go from there now that I'm back on my feet.
 

TJBaker57

Well-Known Member
Wouldn't the live data be coming from the sensor or how does it calculate it?
As for how is it calculated.... I suspect that our temp sensor, being a 2 wire sensor, is a simple thermistor. A thermistor has a resistance that varies with temperature. In my field, HVAC, there is almost universal use of a 10k Negative Temperature Coefficient thermistor for temperature sensing. It matters not where we get them or what configuration they come in, they all have the same temperature vs resistance curve. I wouldn't be surprised if the automotive industry has a similar defacto standard of temperature sensing devices.
 
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MBS1994

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As for how is it calculated.... I suspect that our temp sensor, being a 2 wire sensor, is a simple thermistor. A thermistor has a resistance that varies with temperature. In my field, HVAC, there is almost universal use of a 10k Negative Temperature Coefficient thermistor for temperature sensing. It matters not where we get them or what configuration they come in, they all have the same temperature vs resistance curve. I wouldn't be surprised if the automotive industry has a similar defacto standard of temperature sensing devices.
That's actually the field im trying to get into. I'm type 2 certified and just got through my first AC season at a 450+ plus unit apartment complex. There was something oddly satisfying for me to trouble shoot the problem and then getting it to work again proper. Sorry didn't mean to get so off track there
 
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MBS1994

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So I got the torque pro and not sure what to look at in particular but I ran the tests and only thing to not pass was o2 related
 

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budwich

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All you need to do is monitor the vacuum pid in a dial / gage display while in idle and also at constant medium rpm.
 

TJBaker57

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So I got the torque pro and not sure what to look at in particular but I ran the tests and only thing to not pass was o2 related
Be aware that those tests in Torque Pro are misidentified. Those CID and TID numbers are not what the screen says they are. Somewhere I have the documentation that says what the tests really are, but finding those documents is a whole 'nother matter!
 
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MBS1994

Well-Known Member
Be aware that those tests in Torque Pro are misidentified. Those CID and TID numbers are not what the screen says they are. Somewhere I have the documentation that says what the tests really are, but finding those documents is a whole 'nother matter!
I was wondering that because one of them was right on point and failed but the other side had the exact reading a passed. I'm glad to see I'm not misfiring though that is worth the upgrade to the pro
 

budwich

Well-Known Member
its part of the display setup where you create gages to display (touch and hold screen area). Then the system asked you the type of gage / size / etc and then sends you to the list of parameters that you can choose from... scan down the list, vacuum is there. its might be a gm "extra pid" which you can add in the setup of torque.
 
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MBS1994

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its part of the display setup where you create gages to display (touch and hold screen area). Then the system asked you the type of gage / size / etc and then sends you to the list of parameters that you can choose from... scan down the list, vacuum is there. its might be a gm "extra pid" which you can add in the setup of torque.
I found it it was already on one of the screens by default.
 
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MBS1994

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Replaced my maf and fuel trims were still the same but when I would give it some gas I noticed it would go more negative. I was advised to unplug the maf and o2s and see what it would do. Unsurprisingly it read zero with it all unplugged, o2s in and maf out was within 8 +/-, and then with it all plugged back in my LT was +2. This is the first time I've had positive fuel trims since this started but I still need to go drive and see how it responds
 
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MBS1994

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So it seems like it's only rich if I'm idling, park or drive. When I start driving the fuel trains go way up
 

budwich

Well-Known Member
Replaced my maf and fuel trims were still the same but when I would give it some gas I noticed it would go more negative. I was advised to unplug the maf and o2s and see what it would do. Unsurprisingly it read zero with it all unplugged, o2s in and maf out was within 8 +/-, and then with it all plugged back in my LT was +2. This is the first time I've had positive fuel trims since this started but I still need to go drive and see how it responds
are you talking about the MAP or MAF? What' your vacuum readings at idle and at constant medium throttle?
 
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MBS1994

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are you talking about the MAP or MAF? What' your vacuum readings at idle and at constant medium throttle?
Bought a new maf, other one was a junk yard pull out that I was skeptical about. I'm going to shelf this for a while as Its a back up vehicle. With more reading I'm willing to bet it's a exhaust leak. I have a few broken manifold bolts and I had to chop and customize my y pipe to take cats and I'm no welder. I'll try to extract the broken bolts and have my exhaust professionally done later on but as of now I'm done. Thank you for every reply and all the help, when this is solved I'll post back.
 

budwich

Well-Known Member
good luck. i hope you can address the exhaust manifold... BUT... if there were leaks in the exhaust area, it would like drive the system to demand "rich" (ie. high positive trims) to compensate for "unmetered air". Your system (if I understand), is trying to lean out using the trims.
 
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MBS1994

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Does anyone have any idea on how I could see if the tune is the problem except for switching it out with a untuned ecu
 

budwich

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no idea on the question but I doubt it. You never posted any data on your vacuums at idle and at medium constant throttle. They might tell you something about whether the system is seeing lower vacuum that is expected which could mean a problem with the MAP or a vacuum leak in the engine / intake.
 
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MBS1994

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I looked at vacuum this weekend and idle I want to say was -14 but I can recheck it soon. I have been trying to read more and fix this on my own because I feel bad that we're over 150 posts and still not there. I re-welded my exhaust because on another big LS motor based cars I saw exhaust leaks close enough to the o2 sensors could cause the rich condition. I also found a gm sheet listing what sets off the codes I'm dealing with and I'm within all good ranges. My readings are Baro 81.97 kpa, map 31.99 kpa, maf 6.71 g/s. It also lists "no idle air, throttle, purge control, purge circuit, misfire, map, o2 sensor, fuel injector, airflow" but with my numbers and parts replaced I feel the MAP can be ruled out and torque pro wasn't detecting a misfire. I will be checking my injectors soon as well along with vacuum again.
 

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budwich

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OK... I can only go by limited experience dealing with similar "negative numbers". Anyway, IF you are saying the vacuum at idle was -14? (in./hg), then I would say that is a bit low (ie. not enough vacuum).... but again, based on limited l6 monitoring. Of course, injector issues can also play a large part. However, based on your "side to side", that would indicate problems on BOTH sides which would be hard to imagine is likely. It is more plausible that a fuel pressure problem exists impacting both sides.
 
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MBS1994

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Looking back those are my o2 readings. I put new ones in and the car seems happier, idles smooth, sounds better, fuel trims are coming back up, I still need to drop my exhaust to fix two broken manifold bolts, tighten the o2s all the way, and a couple other things but I'm hopeful.
 

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MBS1994

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Got one of three out, this one being the furthest back on the passenger side. Driver side front is getting a clamp and passenger front is being stubborn might by a clamp for that as well. Also got my o2s more than hand tight now so I'm hoping to throw it all back together soon and see how it does
 

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MBS1994

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How quickly can the ecu detect the rich condition? My numbers are better but still not perfect, it is 14 years old and has 215k so I'm not expecting it to be like new but if the light stays off it's a win
 

budwich

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The system will code once +/- 25 on LTFT is hit for a period of time... not sure how long but it will code once those values are "sustained". You just have to monitor them for a few run cycles to get the idea of where they are heading or not.
 
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MBS1994

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The system will code once +/- 25 on LTFT is hit for a period of time... not sure how long but it will code once those values are "sustained". You just have to monitor them for a few run cycles to get the idea of where they are heading or not.
The car is a lot better so I'm hoping. Haven't been able to drive much but no code so far and when I run the code reader nothing is pending either. Fingers crossed gentleman
 
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MBS1994

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So... confirmation... Car Scanner can indeed import PIDs from a file and display the data. I would need to setup the file as it doesn't use the very same format as Torque or OBD Fusion but that's simple enough. Car Scanner looks to have a number of nice useful graohs and live data monitors that Torque lacks. Here as an example are the injector timings and a shot of custom sensors (pids) imported.

View attachment 96109View attachment 96110
How do I get these ones? And just a update in general, new maf, new o2s, new exhaust manifold gaskets, rewelded the y pipe, and it's got new spark plugs and wires less than 3k miles old
 
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MBS1994

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My coolant on dash showed a tick above 210, vacuum is bottom left. I noticed short term was only slightly negative today so I'm unplugging the battery to try and clear my long term fuel trim and see. I also found multiple spots on my intake somewhat loose so I tightened those down as much as I could.
 

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TJBaker57

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How do I get these ones?

Injector Pulse Width..... The graph I posted was PIDs copied from Torque Pro into Car Scanner Pro... But these are from a 4.2.

I have no idea what is supported on the 5.3 in this platform. Just now I uncovered 2 IPW PIDs for my LM7 5.3 in my 2005 Yukon. For that engine there seems to be just 2 PIDs, an average value for each bank, not individual cylinders.
 
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MBS1994

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Top or 3rd is what will set off the rich condition. So it says Baro > 70KPa. Meaning if my baro is greater than 70 it'll set it or it should be greater when working right? My barometric pressure is 13.05 psi and Google translates it to 89.97 kpa. Recently when I reset the codes it briefly threw a code pending for the map but went away and came as a p0172 and p0175
 

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budwich

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My coolant on dash showed a tick above 210, vacuum is bottom left. I noticed short term was only slightly negative today so I'm unplugging the battery to try and clear my long term fuel trim and see. I also found multiple spots on my intake somewhat loose so I tightened those down as much as I could.
At idle, your vacuum seems a bit too little (not enough). STFT are not a worry in general... they will usually "waggle" between + and - but that depends on where the system is and what it is seeing. Its your LTFT that will eventually set a code... or probably a "sum of both" once that passes +/- 25%. The "baro" is determine by the MAP with its initial Key ON / engine off setting during the initiation of a start. What does your vacuum read with key on / engine off. IF I recall, you indicated a wiring issue to the map at one point. Depending on how that was address, it might be impacting the sensor reading.
 

TJBaker57

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Meaning if my baro is greater than 70 it'll set it or it should be greater when working right?

Those are prerequisite conditions that need to be met for the DTC to set, as I understand it. Meaning that for the DTC test to run, the barometric pressure must be greater than 70 kPa. Similarly, the MAP must be greater than 15 kPa and less than 105 kPa. The coolant temp must be greater than -40 C and less than 139 C. And so on. At least that is how I interpret that column.
 
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MBS1994

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Those are prerequisite conditions that need to be met for the DTC to set, as I understand it. Meaning that for the DTC test to run, the barometric pressure must be greater than 70 kPa. Similarly, the MAP must be greater than 15 kPa and less than 105 kPa. The coolant temp must be greater than -40 C and less than 139 C. And so on. At least that is how I interpret that column.
And maybe I'm focusing to much on the enabling condition and looking at it as if my baro is greater than 70 it'll set just like if its greater than 139c or less than -40c it'll trip. I want to believe it to be that way but I've believed it to be plenty of things at this point
 
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MBS1994

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At idle, your vacuum seems a bit too little (not enough). STFT are not a worry in general... they will usually "waggle" between + and - but that depends on where the system is and what it is seeing. Its your LTFT that will eventually set a code... or probably a "sum of both" once that passes +/- 25%. The "baro" is determine by the MAP with its initial Key ON / engine off setting during the initiation of a start. What does your vacuum read with key on / engine off. IF I recall, you indicated a wiring issue to the map at one point. Depending on how that was address, it might be impacting the sensor reading.
My stft have been over -10 consistently that's why I was optimistic as it was closer to 0 but still very rarely positive. I'll check again tomorrow with key on engine off and get back. So to little vacuum would be a leak somewhere?
 

budwich

Well-Known Member
In my regular monitoring and based on my readings, the STFT typically "oscillate" somewhat in conjunction with the o2 sensors basically as the system responds to trying to keep the expecting mixture required (14:1 or thereabouts). The LTFT is what it is, "long term" (ie. "constant"), is the "coarse" setting. Thus, the system operates at the "point" with the "correction" in and around that point... meaning somewhat "less" (negative) and somewhat "more" positive, relative to 0 not the LTFT point. So even with a significant negative LTFT (-10/-15), it is possible to have both + and - STFT response as the system still attempts to maintain the fuel air mixture ratio. It appears that your system continues to see significant "negativeness" basically moving the "sum" of the two fuel system controls towards -25% which will eventually cause either the pending code or code depending more on how close the LTFT comes to that bogey.

As for whether there is a vacuum leak or not, I would say that is not your problem as a vacuum leak would likely draw in some "unmetered air" for which the system would be compensating with MORE fueling and hence positive LTFT. Again, hopefully we are each talking the same paramters and not "cross talking" (ie. misunderstanding one character letter).

One thing related to your recent data, is the idle rpm. Perhaps the I6 has higher idle (at around 600) so perhaps the V8 is lower, but that value seems a bit low. Does the truck idle well?
Further, related to the vacuum question, the value at the PCM (which you display) is a sensor reading, which could be bad wiring and / sensor OR could be an engine issue in terms of mechanical issue (valve or otherwise). Earlier posts in the thread provided some measuring tests to determine if the MAP sensor is functioning well in terms of responding to vacuum and changes there in. Alternate test to confirm readings would be to get an external vacuum gage and take a "parallel" reading (ie. at idle and at medium constant throttle) to basically confirm the readings. Go from the result. Since the engine itself "appears" to run relatively fine (yes?), it is unlikely to be a mechanical integrity problem, hence my guess is its more to do with electrical "things" (MAP or there in).

One other question, what altitude are you at?
 
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