NEED HELP P0171 on my 04 Trailblazer LT won't go away

[ghost_leader07]

Hi,

I've posted about my issue with the P0171 awhile ago and I'm still chasing it and go no progress I'm no mechanic and I really need to fix this since on mechanic in my country was able to fix it (I'm not from the USA) so here's what I did so far:

-Checked for vacuum leaks with a smoke machine and got none.
-Changed the intake manifold gaskets with Fel-Pro and torqued it to 89 inch pounds
-Cleaned fuel injectors and replaced the o-rings
-Replaced O2 upstream sensor with (ACDelco 213-1698)
-Replaced Fuel pressure regulator with (Standard Motor Products PR233)
-Replaced Fuel Filter (ACDelco GF831)
-Replaced Engine Coolant Temperature Sensor (ACDelco 213-963)

My idle jumped to ~900 rpm after the CEL on but whenever I clear the CEL is goes back to normal also my fuel pressure reading is at 48-49 psi with key on and truck off and about the same when the truck is on... I read online that the fuel pressure specs should be between 50-57 psi I'm using a cheap fuel pressure gauge and I believe my fuel pressure readings are a bit low however it doesn't effect my truck's startup or overall performance I need your input on my fuel pressure readings.

Regarding my fuel trims, I'm using a cheap OBDII scanner and Torque app to monitor my fuel trims after changing the intake manifold gaskets my CEL was cleared both of my STFT and LTFT readings are within +3.5 and -3.5 % even after triggering the P0171 code my STFT and LTFT didn't increase which I guess is strange correct me if I'm wrong but shouldn't my STFT and LTFT be higher than +15% to trigger the code?


I'm very frustrated as my truck ran normally after changing the intake manifold gaskets for about 100mi and I thought my issue was fixed, I'm in a desperate need for the guidance of the veterans of this forum, any help is greatly appreciated.

Thank you in advance.

 

[azswiss]

What did the previous mechanic do to fix the problem last time? How long did the fix last?

Have you graphed the O2 sensors (Upstream & Downstream)? How do they look?

Any misfires or rough idling?

 

[ghost_leader07]

What did the previous mechanic do to fix the problem last time? How long did the fix last?

No mechanics were involved, I was doing the fixes by myself as i mentioned in the list of fixes the only major repair I did was changing the intake gaskets and cleaning the fuel injectors and replacing the o-rings I've also tested the injectors for resistance and all of them showed a unified readings (12.5 ohms) and it lasted for about 100mi or less before triggering the code again.

Have you graphed the O2 sensors (Upstream & Downstream)? How do they look?

I'll upload the graph tomorrow but i believe the readings were normal Upstream sensor fluctuate between 0.1-0.9v and downstream sensor shows a steady 0.6v at idle.

What do you think of my fuel pressure readings? i thinking that i might have a weak fuel pump despite normal startup.

 

[Mooseman]

Check for exhaust leaks. Just dealt with a similar issue and was resolved after fixing leaks. Check for cracks and leaks at the manifold.

 

[ghost_leader07]

Check for exhaust leaks. Just dealt with a similar issue and was resolved after fixing leaks. Check for cracks and leaks at the manifold.

How do you suggest i go about it? I've replaced my cat a while ago and I'm not really content with welding job that was done by the shop, will a leak in before or after cat cause this issue?

 

[TJBaker57]

A leak in the exhaust at the manifold can most definitely cause O2 sensor errors.

 

[ghost_leader07]

A leak in the exhaust at the manifold can most definitely cause O2 sensor errors.

I'll do check for an exhaust leak... thank you.

 

[budwich]

You indicate that you have / did a smoke test .... do you still have access to the smoke machine? If so, see if you can fashion a "plug" to allow you to "smoke" at the tail pipe... ie. pushing smoke up thru the exhaust system. Look for anything happening there after. Of course, it depends on how much smoke you can generate but you might get lucky.

You indicate that your trims are within +-3.5%.... how are you doing the readings AND when are you doing the readings (ie. at idle, cruise, etc). I don't believe the system triggers the fault at those levels... you are likely not monitoring accurately or at the time of the fault. Still further, torque give data capture (freeze frame) at the time of the fault... have you looked at it?

what's your vacuum readings (at idle, at constant medium throttle)?

 

[azswiss]

As @Mooseman said, I would start by checking for exhaust leaks and at the cat welds.

Fuel pressure is close, could be an accuracy issue with the pressure gauge or just barely out of range. Did you run the test with the engine running or just with the key on to get an initial pressurization?

 

[ghost_leader07]

You indicate that you have / did a smoke test .... do you still have access to the smoke machine? If so, see if you can fashion a "plug" to allow you to "smoke" at the tail pipe... ie. pushing smoke up thru the exhaust system. Look at for anything happening there after. Of course, it depends on how much smoke you can generate but you might get lucky.

I still have it but it's not a fancy smoke machine it's just a DIY one with a small air compressor and it can generate good smoke but I'm not sure if it'll be enough to run through the exhaust system but it's worth a try.

You indicate that your trims are within +-3.5%.... how are you doing the readings AND when are you doing the readings (ie. at idle, cruise, etc). I don't believe the system triggers the fault at those levels... you are likely not monitoring accurately or at the time of the fault. Still further, torque give data capture at the time of the fault... have you looked at it?

I did the readings on idle at first then while holding rpm at 2000 the range fluctuates between +/- 10% but it levels around +/- 3% never above -/+5% I'll have to check again since i had to clear the fault once the codes is triggered I'll pull the freeze time data and upload it here for you to check it.

 

[ghost_leader07]

Fuel pressure is close, could be an accuracy issue with the pressure gauge or just barely out of range.

is barely out of range ok and won't cause a lean condition?

Did you run the test with the engine running or just with the key on to get an initial pressurization?

I did both and the pressure stayed relatively at the same level -/+ 48 psi, i want to do a leak down test but I don't know what pressure drop considered normal however i know if the pressure drops instantly it means there's an issue with fuel system but what about a slow pressure drop what percentage considered normal?

 

[azswiss]

If low fuel pressure is the problem then you should see fuel trim increases to compensate. Freeze frame data is going to be key.

 

[budwich]

I still have it but it's not a fancy smoke machine it's just a DIY one with a small air compressor and it can generate good smoke but I'm not sure if it'll be enough to run through the exhaust system but it's worth a try.


I did the readings on idle at first then while holding rpm at 2000 the range fluctuates between +/- 10% but it levels around +/- 3% never above -/+5% I'll have to check again since i had to clear the fault once the codes is triggered I'll pull the freeze time data and upload it here for you to check it.

But what about the "HOW"... are you watching the readings with "dial display" or "graph". there might be some delay on how much / how fast torque can get some datas. Further some "dials" keep min / max ranges while displaying "current" reading. I would find it some what strange that an exhaust manifold leak would not show "long term" values approaching the trigger for the code while monitoring. Can you provide your vacuum readings as it possible that the MAP isn't acting "well".

 

[ghost_leader07]

But what about the "HOW"... are you watching the readings with "dial display" or "graph". there might be some delay on how much / how fast torque can get some datas. Further some "dials" keep min / max ranges while displaying "current" reading. I would find it some what strange that an exhaust manifold leak would not show "long term" values approaching the trigger for the code while monitoring. Can you provide your vacuum readings as it possible that the MAP isn't acting "well".

I was monitoring it with both digital and dial display and you're correct there's a delay in receiving the data, I'll drive for a bit to trigger the fault code again and get you the freeze time data as soon as possible and as far as my MAP sensor I've replaced it with Delphi part thinking it was the issue before, where should the vacuum readings be at?

 

[budwich]

There should be significant vacuum at idle as the throttle body is basically closed. At constant medium throttle, it should be cut quite a bit ( half or more).
Having said that, you mentioned that you are "outside NA"... are you sure about the fuel supply that you are getting, in terms of quality / components (water, alcohol... less than 10%, "clean-ness", etc). I would still expect the system to move trims to attempt to correct for these but perhaps there is other factors than can drive the code without trim out of bounds issues.

On the "map replacement", I have had "off shore MAP's" not function correctly as supposedly new... could be the supplier or the maker... assuming you have a "real part" and not a "knock off". The "bad MAP" readily caused trim issues. It can be tested with a vacuum pump to determine if it responds correctly.... basically the test is done with engine off, MAP unplugged from engine, key on, read vacuum values from torque while reading vacuum pump gage and compare results at various levels.

Of course, further indicate that maybe the fuel pressure readings might be "suspicious" because of the meter or otherwise. Without confirming the meter, it would be tough to ensure the fuel pump is functioning at capacity... ie. might work at idle but at demand, it is not capable of adequate delivery. Again, I would think the system would still try to trim the system up to compensate until the code was set.

 

[ghost_leader07]

UPDATE:

I was checking the exhaust for leaks by letting the car on idle and blocking the tailpipe with a rag i can definitely hear hissing sound around the cat which i replaced a while ago but i didn't hear anything around the exhaust manifold.

I need a better scan tool since my cheap one is giving me inaccurate readings and disconnects randomly.

However after doing another diagnosis a new fault code appeared alongside the P0171 which P0136: O2 Sensor Circuit Malfunction (Bank 1 -Sensor 2)

Will an issue with the downstream O2 sensor cause a lean condition?

Much appreciation for your help

 

[Mooseman]

UPDATE:

I was checking the exhaust for leaks by letting the car on idle and blocking the tailpipe with a rag i can definitely hear hissing sound around the cat which i replaced a while ago but i didn't hear anything around the exhaust manifold.

I need a better scan tool since my cheap one is giving me inaccurate readings and disconnects randomly.

However after doing another diagnosis a new fault code appeared alongside the P0171 which P0136: O2 Sensor Circuit Malfunction (Bank 1 -Sensor 2)

Will an issue with the downstream O2 sensor cause a lean condition?

Much appreciation for your help

No. All it does is report how efficiently the cat is working.

Did you check around the manifold for a leak? The leak at the cat is probably too far from the O2 sensor in the manifold to affect it. Maybe a minor leak at the manifold to pipe connection could.

I'd check again for a vacuum leak using carb cleaner instead. A smoke machine may not show one without a vacuum being applied in the case of a marginal gasket.

 

[ghost_leader07]

I'd check again for a vacuum leak using carb cleaner instead. A smoke machine may not show one without a vacuum being applied in the case of a marginal gasket.

I'll do a check with carb cleaner again I'll make sure to be thorough to eliminate the cause of a vacuum leak.

I did some live data test with my odb2 scanner (possibly faulty) and readings were inconsistent and strange at times here's a few screenshots of the test i did.




My fuel trim readings are quite strange i suspect my cheap obd2 scanner as my engine temperature drops to -40c and my engine's rpm drops to 50 rpm as well massive delays and incorrect readings... I won't be able to get an accurate readings with this obd2 scanner i believe it's faulty.

I'd like your input about this

Thanks in advance,

 

[azswiss]

@ghost_leader07 said I did some live data test with my odb2 scanner (possibly faulty) and readings were inconsistent and strange at times here's a few screenshots of the test i did.

This is real data, the OBD2 scanner does not make measurements, it reports what the sensors actually observe. Scanner faults would affect connectivity and update frequency but not the displayed data.

Based on the intermittent behavior of Sensor 2 you might want to check the connector and wiring.

 

[ghost_leader07]

This is real data, the OBD2 scanner does not make measurements, it reports what the sensors actually observe. Scanner faults would affect connectivity and update frequency but not the displayed data

OK, Can you explain why I'm getting sudden -40c temperature drops or incorrect rpm, i also get -99% on STFT for brief moments i honestly believe either my crappy obd2 bluetooth scanner is faulty or something else.

What do you think is going on with my fuel trims and o2 sensor behavior?

I'll take my truck for mechanic to get accurate readings and rule out an issue with my odb2 scanner

 

[azswiss]

I cannot explain the temperature drop, RPM drop or the STFT spikes.

The scanner dongle connects to the vehicle's data bus and passes the digital data (in Hexadecimal format), as reported by the PCM, to the Torque app for decoding & display. It does not access analog data (voltage, injector pulse width) from individual sensors.

This is what the PCM is actually seeing and responding to.

Based on the range of the issues you have observed it is possible there may be more than one underlying problem. Any luck getting freeze frame data?

Wish I had more to offer.

 

[ghost_leader07]

Based on the range of the issues you have observed it is possible there may be more than one underlying problem. Any luck getting freeze frame data?

I'm having a bit of trouble with that torque app won't show anything in freeze frame data section but the codes are in pending nothing is confirmed yet maybe that's why nothing is showing in freeze frame data,

Another thing caught my curiosity regarding my brake booster i did a couple of tests on it and it seem to be functional (3 presses on the brake pedal with the key off and it stiffen on my 3rd press) but if i did a couple of quick pushes with engine running my idle increases a little and i can hear a loud hissing sound as i press on rapidly is it normal to make a hissing sound if pushed quickly with the engine running?

Thank you again for your time and input

 

[azswiss]

Freeze frame data is only captured when the code actually sets (becomes Current vs. Pending).

The hiss combined with the RPM bump indicates a vacuum leak; this should not be happening and must be fixed.

With the engine running and while graphing STFT, pump the brakes and see if there is any change in STFT.

 

[ghost_leader07]

Freeze frame data is only captured when the code actually sets (becomes Current vs. Pending).

Got it! I'll wait for the truck to set a fault code.

The hiss combined with the RPM bump indicates a vacuum leak; this should not be happening and must be fixed.

The hiss happens when the truck is idling while pressing on the brake pedal rapidly it's very audible and the rpm bump is not high it's like 100-200 rpm above the normal idle ~600 rpm

I'll take a video of that and post here to have a better idea, if it is not normal it could be the cause of the P0171 that i'm struggling with i really hope it's the brake booster what's failing. 🤞

 

[Mooseman]

Another thing caught my curiosity regarding my brake booster i did a couple of tests on it and it seem to be functional (3 presses on the brake pedal with the key off and it stiffen on my 3rd press) but if i did a couple of quick pushes with engine running my idle increases a little and i can hear a loud hissing sound as i press on rapidly is it normal to make a hissing sound if pushed quickly with the engine running?

That is normal operation of the brake booster. If after stopping the engine for a while it still holds vacuum and lets you pump them about 3 times, like you did, it looks to be leak free. However, do check the hose that goes from the intake to the booster for an external vacuum leak.

 

[budwich]

the obd interface "dongle" that you are using can have issues as there are a number of elm327 "copies" on the market. I have had ones that can not read certain pids within torque. It is plausible that your unit isn't reliable. In addition, there are some parameters within torque setup that can also impact the communications. You should check the settings that are being used. Of course, there are ways to do some checks to some what verify what is happening. You can get another one and / or try another vehicle and see if the operation is more stable. Go from the results.

 

[ghost_leader07]

That is normal operation of the brake booster. If after stopping the engine for a while it still holds vacuum and lets you pump them about 3 times, like you did, it looks to be leak free. However, do check the hose that goes from the intake to the booster for an external vacuum leak.

I've checked the hose and it doesn't leak but here's a few videos of air noise i mentioned it's quite loud especially when i press the pedal hard in park

 

[ghost_leader07]

the obd interface "dongle" that you are using can have issues as there are a number of elm327 "copies" on the market. I have had ones that can not read certain pids within torque. It is plausible that your unit isn't reliable. In addition, there are some parameters within torque setup that can also impact the communications. You should check the settings that are being used. Of course, there are ways to do some checks to some what verify what is happening. You can get another one and / or try another vehicle and see if the operation is more stable. Go from the results.

Thanks for the suggestion, i don't have much confidence in my obd2 scanner to be honest especially with communications issues, i didn't do any adjustments in the app other than adding custom PIDs for GM, I thinking of ordering a decent scanner like BlueDriver or OBDLink MX+ or if you know a good scanner that has good features.

 

[Mooseman]

Videos show as unavailable. Did you make them public?

 

[ghost_leader07]

Videos show as unavailable. Did you make them public?

Sorry i forgot, they're public now

 

[Mooseman]

Although it kinda sounds loud in the videos, it's normal for the operation of the booster. If it was continuous without pressing on the brake, that would be a problem.

 

[budwich]

You still have never posted any info on your vacuum readings as requested. Further, when posting and questioning your data results, you need specifically identify what parameters exactly are being display to ensure people aren't guessing at what you did... oops I see at the bottom of graphs the ones are identified.

Having said that, IF the graphs posted of the trims are correct parameters, then this DOES NOT correlate with what you posted and said earlier about your trims being +/- 3.5%... something is not correct about what you are saying. Again, as I indicated, what PID's are you actually looking at when you make your statements.

You need to verify your elm327 device.... find another vehicle... surely there are other friends or neighbors with cars that will let you look at some data for a few minutes (although scanning for pids might take a bit... if you need to scan). Having said that, based on some of the posts, it appears that the elm is working OK. I still suspect a MAP issue (wiring or otherwise) and / or vacuum related issue.

edit: Re-looking at your trims, your system indicates that too much fuel is being dumped into engine and it is trying to compensate by reducing the trim level. Thus, this could be the result of insufficient air (not excess air) or possibly insufficient fuel pressure to allow proper "spray formation" at the injectors. Have you looked at your misfire counts? Further, depending on how warm the engine was when you posted your O2 graphs, the "waggling" of the downstream sensor suggests either a sensor issue or a cat problem. IF your system has been running with excess fueling, then your cat might be damaged. How is your gas mileage?

edit2: what is your adapter status showing for error counts?

 

[ghost_leader07]

Although it kinda sounds loud in the videos, it's normal for the operation of the booster. If it was continuous without pressing on the brake, that would be a problem.

All right i can rule out a brake booster leak for now, I'll continue to search for the source of the leak if any is present.

 

[ghost_leader07]

You still have never posted any info on your vacuum readings as requested. Further, when posting and questioning your data results, you need specifically identify what parameters exactly are being display to ensure people aren't guessing at what you did... oops I see at the bottom of graphs the ones are identified.

Having said that, IF the graphs posted of the trims are correct parameters, then this DOES NOT correlate with what you posted and said earlier about your trims being +/- 3.5%... something is not correct about what you are saying. Again, as I indicated, what PID's are you actually looking at when you make your statements.

You need to verify your elm327 device.... find another vehicle... surely there are other friends or neighbors with cars that will let you look at some data for a few minutes (although scanning for pids might take a bit... if you need to scan). Having said that, based on some of the posts, it appears that the elm is working OK. I still suspect a MAP issue (wiring or otherwise) and / or vacuum related issue

Thank you for taking the time and effort to respond, I've tested my elm327 device and it appears to have some commutation issues with my truck sometimes it works and i can get some live data with strange readings and other times i get none so i guess we can't take any of the data i got as an accurate reading however I've attached screenshots using the same scanner on my truck and a dodge and the readings were accurate and with very slight delay my truck.


Both O2 sensors refused to send any data also the delay was like 3-4 sec difference and all over the place on my truck, both vehicles were at operating temperature i've even took it on a short ride but no luck it's highly unlikely that my ECU is sending weird data or not sending at all my truck runs fine, i'll definitely need a better obd2 scanner with better live data function so i can provide you with accurate readings. i'm planning on taking my truck to an auto shop this week and get my readings accurately!

Oh i forgot to mention i did clear my fault codes and drove it for about 25 miles also my readiness check on torque app for both of my o2 sensors and cat stating "not complete" could it be why both of o2 sensors aren't giving any readings?

edit: Re-looking at your trims, your system indicates that too much fuel is being dumped into engine and it is trying to compensate by reducing the trim level. Thus, this could be the result of insufficient air (not excess air) or possibly insufficient fuel pressure to allow proper "spray formation" at the injectors.

I haven't changed my air filter in awhile but it looks fairly clean nothing excessive, My fuel pressure is at 48-49 psi with key on and no change with engine running no issues with starting up.

Have you looked at your misfire counts?

I'm getting strange misfire counts on all cylinders something like 32,000 but i believe obd2 scanner is at fault here now that I've confirmed its commutation issues with my truck in particular again no instant data massive delays in the live data feed.

Further, depending on how warm the engine was when you posted your O2 graphs, the "waggling" of the downstream sensor suggests either a sensor issue or a cat problem. IF your system has been running with excess fueling, then your cat might be damaged

I had this lean condition for a while now even before changing my original cat, I've installed a MagnaFlow cat so it possible that my cat is damaged due to the lean condition do you suggest i replace it? i could delete it for now until i fix the P0171 and install a new one later.

How is your gas mileage?

Oh i believe it's pretty horrible i haven't measured it to be honest but it feels like having a ghost V8 6.0L engine on my truck which i don't mind if it WAS a V8 6.0L


Sorry for being lengthy and thank you again for your time.

 

[azswiss]

With multiple PIDs showing abnormal/intermittent/erratic responses I almost wonder if there might be a Ground problem in the mix.

 

[ghost_leader07]

With multiple PIDs showing abnormal/intermittent/erratic responses I almost wonder if there might be a Ground problem in the mix.

I don't think i have a ground problem since i don't have drivability issues and my truck is rust free, i genuinely believe my cheap $8 obd2 scanner is just acting up, I've tested on a Dodge RAM and it connected and preformed okay then i got a random -40 degrees reading for brief moment same as my truck. i'd have to use a good scanner to eliminate these false readings.

 

[mrrsm]

You also have 2-3 more places to investigate for possible Vacuum Leaks:

(1) If your Trailblazer HAS the SAIS System as described in this Diagram...



...AND since you have a persistent P0171... The SAIS Solenoid shown below can STICK OPEN and cause this problem...



(2) Alternatively, if your Trailblazer LL8 Engine Does NOT have the SAIS System... it will STILL have a Block Off Plate centrally located on the Passenger Side of the Engine Head...



If so...THIS invites the possibility of either having a CRACKED Aluminum Block Off Plate OR the Block Off Plate Fasteners may have come LOOSE, allowing Unregulated AIR into the Engine Head...



(3) If your Block Off Plate Gasket has become cracked or damaged, Unregulated AIR can enter the Engine Head as a result...

 

[budwich]

good effort on getting thru things. hopefully, you are heading in the right direction. BUT... and I know there is lots in the posts... did you look at the status of the obd elm device for error counts... that will tell if there are communication issues. Next, get a meter and measure / check your coolant sensor.... to confirm that the sensor is working correctly. That one sensor will cause your problem IF the system thinks it is in cold weather operation.
Further, your code is not an "air leak problem" in terms of excess air getting into the fueling / air. Your problem is too much fuel or too little air. what pid are you providing with the "intake"... that is not an absolute vacuum reading which was still not provided. I highly doubt that your elm is a problem (might have some issue but entirely bad) since it appears to function on another vehicle. You may have wiring issues or otherwise (power / grounding). I would suggest that you focus on the coolant temp first and then the MAP as those two areas are candidates.

finally, hopefully your trip to the shop will provide a printout and further info on what they see ... without "stealing your wallet"

 

[ghost_leader07]

You also have 2-3 more places to investigate for possible Vacuum Leaks:

(1) If your Trailblazer HAS the SAIS System as described in this Diagram...

View attachment 101834

...AND since you have a persistent P0171... The SAIS Solenoid shown below can STICK OPEN and cause this problem...

View attachment 101835

(2) Alternatively, if your Trailblazer LL8 Engine Does NOT have the SAIS System... it will STILL have a Block Off Plate centrally located on the Passenger Side of the Engine Head...

View attachment 101836

If so...THIS invites the possibility of either having a CRACKED Aluminum Block Off Plate OR the Block Off Plate Fasteners may have have come LOOSE, allowing unregulated AIR into the Engine Head...

View attachment 101837

(3) If your Block Off Plate Gasket has become cracked or damaged, Unregulated AIR can enter the Engine Head as a result...

View attachment 101838

Thank you so much for your comprehensive reply,

I had SAIS system on my truck and thought it might be the cause so I've deleted it and got a block off plate from the junkyard and installed it so i guess we can eliminate this area.

 

[ghost_leader07]

did you look at the status of the obd elm device for error

Where can I check for the status?

Next, get a meter and measure / check your coolant sensor.... to confirm that the sensor is working correctly. That one sensor will cause your problem IF the system thinks it is in cold weather operation.

I took @Mooseman advice on replacing the ETC sensor when I was working on the intake manifold gaskets replacement and it's brand new ACDelco part so i think we can eliminate the ETC sensor.

Further, your code is not an "air leak problem" in terms of excess air getting into the fueling / air. Your problem is too much fuel or too little air. what pid are you providing with the "intake"... that is not an absolute vacuum reading which was still not provided

Where can I find the pid you're asking for? and absolute vacuum reading as well? I'm only seeing MAP reading and intake air temperature on my scanner.

I highly doubt that your elm is a problem (might have some issue but entirely bad) since it appears to function on another vehicle.

My elm connects to my truck fairly quick and i can get the error codes no problem but when it comes to live data it's all over the place, can you elaborate what ground issue would cause these delays in readings I've checked my ground connections around the ECU, engine and fuse box and all of them are secured and clean...if there's a ground issue it'll be an endless rabbit hole for sure especially for someone with a little knowledge as myself 😅 but can I have a ground issue while my truck is driving "normally"?

I did mention something about testing my elm device on another vehicle which happened on my truck as well and that is the -40c engine temperature drops i even hear the torque app warning voice of "icy condition" which doesn't make any sense.

I would suggest that you focus on the coolant temp first and then the MAP as those two areas are candidates.

What exactly should I look for in the MAP sensor data?

finally, hopefully your trip to the shop will provide a printout and further info on what they see ... without "stealing your wallet"

Oh they tend to do that around here but with a little bit of knowledge i can protect my wallet from them at least for the time being.

Sorry for the many questions but I want consume as much information as possible 😅