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Discussion Starter #1
First off Thanks to this forum which has already helped me on a few occasions. On my 2011 acadia I am getting a number of trouble codes (P0121, Throttle position sensor: P0221, Accelerator position pedal sensor and P2176 throttle position idle not learned) This of course results in the message being displayed on the dash, service stabilitrak, service traction control, engine powere is reduced. I was having the issues a month or so ago and took off the throttle body (which was quite dirty with varnish/oil) and cleaned it up really good. It ran like a dream for a couple of weeks. Now its worse than ever. Just wondering if anyone has experience with this. I'm going to check all the wires at the throttle body wiring harness tomorrow as it seems there is a good chance it's a broken wire but I'd really appreciate any helpful comments. Also I get a P2099 code once in a while( it used to only come on after a fuel fill followed by highway driving but now its coming back more often) thanks everyone in advance.
 

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There are two throttle position (TP) sensors. P0121 is a performance error for TP 1 and P0221 is a performance error for TP 2. The operate backwards from each other - TP 1 is high (close to 5V) at idle (not touching the pedal) and TP 2 is low (close to 0V).

Performance errors set when one TP sensor disagrees greater than 9 percent from the other TP sensor, or the TP sensor disagrees greater than 9 percent from the predicted value for greater than 1 second or a cumulative of 10 seconds.

Because both sensors are causing a performance code, I'm guessing that they both are disagreeing with the predicted value.

P2176 sets when:
    •  The ECM detects that the TP sensor 1 voltage is not between 4.12-4.55 volts after the throttle learn procedure, with the throttle at rest.
    •  The ECM detects that the TP sensor 2 voltage is not between 0.34-0.99 volts after the throttle learn procedure, with the throttle at rest.

The diagnosis aids for P2176 specifically say to ignore it and troubleshoot the other TP codes if there are any present. So, I guess you shouldn't do a re-learn procedure until you know your sensors are good. The P2099 may be caused by the other faults, so I'd ignore it also for now.

So... You can see if your sensors are FUBAR yourself or take it to the dealer and see if you're covered by the special adjustment. If you have a scanner that can read real-time values and know how to use a multi-meter, the diagnosis is pretty straight forward. Also, tell me if I'm wrong, but I'm assuming both sensor codes set initially, before you tackled any work on your own.

SIDENOTE: I wish people would title the thread with the actual fault codes, not with "power reduced, service traction control", because that tells us nothing. All powertrain and some body codes produce that message.
 

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lamping.ap said:
SIDENOTE: I wish people would title the thread with the actual fault codes, not with "power reduced, service traction control", because that tells us nothing. All powertrain and some body codes produce that message.
5,5 - 2,2 ;D ;D
 

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Discussion Starter #5
Speleos:
Thanks for the link to the other thread. (#14582 - Special Coverage Adjustment - Throttle Body - Reduced Power Mode) It says free of charge for vehicles covered with Vehicle Service Contracts which is not me, I'm concerned it will cost too much anyway I will call the local dealership and ask. Also Today I got a new code P0101. i'm starting to think it could be a problem with a ground on the PCM?? I agree with regard to ignoring the p2099 code for now.

Lamping:
Thank you fro shedding some light on how the TP sensors function. Yes i can view/log real time data with my scan tool/app (torque) and am handy enough with my multi-meter. I can't remember exactly if both codes (P0221 and P0121) were set initially It might have been the P2176 at the beginning but what made me take off the TB for cleaning was the Reduced Engine Power warning. I few guiding words on how to diagnose the TP sensors myself would be really helpful ( my budget is very minimal but at least my DIY pockets go deep)

I still think I will find a cracked wire this evening when I take apart the wiring harness (now maybe the MAF sensor wiring harness too) :banghead:
 

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Discussion Starter #6
lamping.ap said:
SIDENOTE: I wish people would title the thread with the actual fault codes, not with "power reduced, service traction control", because that tells us nothing. All powertrain and some body codes produce that message.
Thanks for the tip I will title threads with fault codes from now on. I didn't realize that the traction contro stabilitrak engine power message was so common
 

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Saskmaster said:
Speleos:
Thanks for the link to the other thread. (#14582 - Special Coverage Adjustment - Throttle Body - Reduced Power Mode) It says free of charge for vehicles covered with Vehicle Service Contracts which is not me, I'm concerned it will cost too much anyway I will call the local dealership and ask. Also Today I got a new code P0101. i'm starting to think it could be a problem with a ground on the PCM?? I agree with regard to ignoring the p2099 code for now.
You're covered for this as long as the car is within the time/mileage limit.

"Special Coverage Adjustment
This special coverage covers the condition described above for a period of 10 years or 120,000 miles (193,000 km), whichever occurs first, from the date the vehicle was originally placed in service, regardless of ownership."
 

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Discussion Starter #8
Speleos said:
You're covered for this as long as the car is within the time/mileage limit.

"Special Coverage Adjustment
This special coverage covers the condition described above for a period of 10 years or 120,000 miles (193,000 km), whichever occurs first, from the date the vehicle was originally placed in service, regardless of ownership."
The dealership will do the Special Coverage Adjustment :) :thumb: But Should I wait until the TP sensor codes return? Also If it is a broken wire and not the TP sensor Will I end up having to pay for that repair, I'm guessing probably. Anyway thanks again for the help
 

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Saskmaster said:
But Should I wait until the TP sensor codes return? ...
What if it doesn't??


Saskmaster said:
... Also If it is a broken wire and not the TP sensor Will I end up having to pay for that repair, I'm guessing probably.
Maybe not if they find it after the TB is replaced. :shrug:
 

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You cleared the codes? You're probably going to have to wait for them to come back, which shouldn't take long if there is an issue. Is it still running rough?

Why do you think there is a broken wire?

Using torque:
  • What are the two sensor values with the car ON, engine ON, throttle - CLOSED?
  • What are the two sensor values with the car ON, engine ON, throttle - WOT?
Here is the throttle body connector pinout:
 

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Discussion Starter #11
Yes I cleared the codes. It's cold up here in Saskatchewan and the remote start is more than a luxury. I think it might be a broken wire because the problem is so intermittent and whenever i fiddle around with the TB wiring harness it gets better or sometimes worse. The Acadia seems to be running fine now this morning the reduced engine power bla bla bla warning came on then went off right away (NO CEL light or code though). Currently the rpm needle only has a very small twitch at idle but stumbles/hesitates with big bounces between 2 and 2.5 k rpm this was happening really bad for a while and now only infrequently.

I checked for the values using Torque (which i just upgraded to the pro. definitely worth throwing these guys a few bucks for what they've done for me also I needed more sensor data)
Absolute throttle position B [47] idle 16.08% (can't figure out how to see voltage) 34.51% Wide Open
ccelerator PedalPosition D [49] idle 19.22%, 60.78% Wide Open
Accelerator PedalPosition E [4a] idle 19.22%, 61.18% Wide Open
Accelerator PedalPosition F [4b] NO DATA???

I'm not sure if the letters correspond to the pinouts but if they do channel F should have a signal right?

Why can't I post images or links?
 

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Discussion Starter #12
lamping.ap said:
You cleared the codes? You're probably going to have to wait for them to come back, which shouldn't take long if there is an issue. Is it still running rough?

Why do you think there is a broken wire?

Using torque:
  • What are the two sensor values with the car ON, engine ON, throttle - CLOSED?
  • What are the two sensor values with the car ON, engine ON, throttle - WOT?
Here is the throttle body connector pinout:
thanks

See above post
 

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Saskmaster said:
Why can't I post images or links?
You should be able to post links now. There's a post counter that prevents noobs from doing that (I think it's 5 posts). The attachment function (for files, pics, etc) hasn't worked in ... ... like ... ... FOREVER!! (at least the last 3-4 years ;D ) Admin2 and his techies seem to ignore the problem although it's been brought to their attention numerous times. :sosad: You'll need to use the 'insert image' function in the reply menu to post pictures from a web-based photo-caching site (the Forum Gallery, Photobucket, Facebook, etc.).
 

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electbc said:
Just for curiosity Sask, open up your air intake to the throttle body and see if you have a milkshake working in there.
He already cleaned it. See the first post.

OP:
You don't want the accelerator pedal position. You want both throttle position sensors. Maybe later when the wife gets home with the Acadia, I can check what actual names of the PIDs are.
 

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Discussion Starter #16
lamping.ap said:
He already cleaned it. See the first post.

OP:
You don't want the accelerator pedal position. You want both throttle position sensors. Maybe later when the wife gets home when the Acadia, I can check what actual names of the PIDs are.
Yes cleaning the intake was step one back a few months ago. Yes I will look again for the throttle position PIDs. If I can't seem to find them I'll ask you to find them for me.. I have a couple codes back now p0101 MAF code and the p2176 (Still no more enginepower blablab or p0221 or p0121) This MAF code is bugging me and throwing a wrench in to my hypothesis, It's come twice in a few days now but I'v never seen it over the last few months I've been chasing this problem.
 

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Yes the throttle plate was dirty and has been cleaned, but do/did you have the milkshake forming in the snorkel? Creamy looking gunk which is sitting in the snorkel. Check the posts on "milkshake" on these forums. I went through a lot of reduced engine power throttle body problems with the polar vortex last winter.
A lot of folks had similar problems last winter. The first time it happened was new years eve 2014, 10 degrees F, 65 mph down the thruway, ding ding ding. Stabilitrack disabled, service stabilitrack, traction control disabled. Reduced Engine Power. I couldn't get more than 30mph, sat on the side of the road for 10 minutes engine off, start it up and go on my way the rest of the way home with no problems.
My MAF sensors were lasting anywhere from a few days to a month. The moisture in the snorkel was killing them. Check my posts on here and outlookforums.
If you have the milkshake in the snorkel, I would recommend performing the PCV barb modification to help alleviate the moisture in the air intake and the blow by of oil. Easy enough to do, and a world of difference. I strongly recommend doing this simple, free modification, and then change the MAF sensor.
If you want information on the Modification to the PVC barb here is the link to the Camaro forum.
http://www.moderncamaro.com/forum/v6-engine-discussion/53385-llt-lfx-pcv-orfice-mod-importance.html

I assume that you also received a letter from GM regarding extended coverage for the Throttle Body. If you have throttle problems they will replace it with in the 120,000 miles I believe. After all my issues I also replaced the throttle, on my dime because it was after the 120k. It has been a year since I had any issues and I now have over 176,000 miles. It hasn't been as cold for us this year, but I also don't loose so much oil and I don't have the milkshake, just residual oil in the snorkel.
 

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P0101 "Mass Air Flow (MAF) Sensor Performance" sets when:
    •  The ECM detects that the MAF sensor signal is greater or less than the calculated air flow based on engine load and engine speed.
         OR
    •  The ECM detects that the MAF sensor signal is greater or less than the calculated air flow, and The ECM detects a significant error in the long term fuel trim at cruising speed.

It will NOT set if DTC P2176 is set. This is probably why you didn't see it before. This time the P0101 must have set first, followed by the P02176. The calculation is based on throttle among other things.

Take the car to the dealer and get the throttle body checked out, since it's free. Make sure you fill them in on the other previous codes as well.

Also, I looked in Torque and didn't see the correct parameters. You need better scantool software, or the info to add custom PIDs into Torque to read them.

Can you post the freeze frame data associated with those codes?
 

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electbc said:
Yes the throttle plate was dirty and has been cleaned, but do/did you have the milkshake forming in the snorkel? Creamy looking gunk which is sitting in the snorkel. Check the posts on "milkshake" on these forums. I went through a lot of reduced engine power throttle body problems with the polar vortex last winter.
A lot of folks had similar problems last winter. The first time it happened was new years eve 2014, 10 degrees F, 65 mph down the thruway, ding ding ding. Stabilitrack disabled, service stabilitrack, traction control disabled. Reduced Engine Power. I couldn't get more than 30mph, sat on the side of the road for 10 minutes engine off, start it up and go on my way the rest of the way home with no problems.
My MAF sensors were lasting anywhere from a few days to a month. The moisture in the snorkel was killing them. Check my posts on here and outlookforums.
If you have the milkshake in the snorkel, I would recommend performing the PCV barb modification to help alleviate the moisture in the air intake and the blow by of oil. Easy enough to do, and a world of difference. I strongly recommend doing this simple, free modification, and then change the MAF sensor.
If you want information on the Modification to the PVC barb here is the link to the Camaro forum.
http://www.moderncamaro.com/forum/v6-engine-discussion/53385-llt-lfx-pcv-orfice-mod-importance.html

I assume that you also received a letter from GM regarding extended coverage for the Throttle Body. If you have throttle problems they will replace it with in the 120,000 miles I believe. After all my issues I also replaced the throttle, on my dime because it was after the 120k. It has been a year since I had any issues and I now have over 176,000 miles. It hasn't been as cold for us this year, but I also don't loose so much oil and I don't have the milkshake, just residual oil in the snorkel.
What codes were your car throwing? This: "Stabilitrack disabled, service stabilitrack, traction control disabled. Reduced Engine Power." tells us very little in trying to compare your issue with his.

The car defaults to one of two failure modes for only the current drive cycle under specific conditions. One failure mode only allows 3rd gear, while the other allows 5th. The OP is not getting stuck in at low speeds like you were. It's possible that the situations are related, but not enough info is provided to agree 100%.
 

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Discussion Starter #20
lamping.ap said:
What codes were your car throwing? This: "Stabilitrack disabled, service stabilitrack, traction control disabled. Reduced Engine Power." tells us very little in trying to compare your issue with his.

The car defaults to one of two failure modes for only the current drive cycle under specific conditions. One failure mode only allows 3rd gear, while the other allows 5th. The OP is not getting stuck in at low speeds like you were. It's possible that the situations are related, but not enough info is provided to agree 100%.
I had a bit of milkshake in the intake but not as much as I have seen/heard others having. anyway I have already done the pcv barb modification. most of the time i do get stuck in the low speed failure mode ( I just learned about these two modes when i read this) Also when I cleaned the TB cleaned the milkshake replace air filter and did the barb mod I also cleaned the MAF (not with WD40 but the good MAF sensor clean stuff) after that I had fabulous throttle response improvement and the best highway mileage I've seen for the Acadia. This lasted about a month and now things are in the current staet

UPDATE: Wife was on the highway today and it went in to low power (Stabilitrack disabled, service stabilitrack, traction control disabled. Reduced Engine Power) mode. When I get home from work I'll check to see if there are any new codes. The plan is to take it Monday to the shop and hopefully get the TB repalced under the "#14582 - Special Coverage Adjustment - Throttle Body - Reduced Power Mode". I hope the TP sensor codes are back.
I'll update If i get any new info.

Thanks folks for the continued help
 
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