Service bulletin for hybrid bump/jerk issue

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aochime

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Hi. I have been experiencing what has been called the "bump/jerk" on GMC hybrid trucks. The symptoms include a jerking sensation as the vehicle switches between hybrid mode and engine mode. This can also cause pauses in acceleration or also sudden accelerations at low speeds. This is typically accompanied by OBD-II codes P2797 (Auxiliary Transmission Fluid Pump Performance) and/or P0C2B (Auxilliary Transmission Fluid Pump Control Module Feedback Signal) and/or P0AC4 (Hybrid Powertrain Control Module Requested MIL). This may also cause other systems to illuminate the Check Engine light - in my case, there was an Emissions System Not Ready OBD-II error.

There was an unofficial bulletin floating around but I came across a PIP (preliminary information post) from GM and the NHTSA. This bulletin specifies the first resolution for this issue is to replace the auxiliary transmission fluid pump control module (GM Part Number 24261817) and a couple of harnesses (24259589 and 24259590). There were some early reports that the control module was only available from a GM service center but it seems these are now available online as well. Parts & Labor this was a $637 fix and it seems to be working. Not sure how easy this replacement is for you DIYers.

If the control module is *not* this fix, then the next step is to replace the auxiliary transmission itself, which is about a $1200 fix.

The GM bulletin can be found at https://static.nhtsa.gov/odi/tsbs/2018/MC-10154554-9999.pdf
Hello, I have the same issue going on with my truck. I ordered the parts you mentioned above. It’s not with the dealer. It’s with a local mechanic. He put the parts on, but he said it needs to be programmed. Have you heard of that before??
 

aochime

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Hi. I have been experiencing what has been called the "bump/jerk" on GMC hybrid trucks. The symptoms include a jerking sensation as the vehicle switches between hybrid mode and engine mode. This can also cause pauses in acceleration or also sudden accelerations at low speeds. This is typically accompanied by OBD-II codes P2797 (Auxiliary Transmission Fluid Pump Performance) and/or P0C2B (Auxilliary Transmission Fluid Pump Control Module Feedback Signal) and/or P0AC4 (Hybrid Powertrain Control Module Requested MIL). This may also cause other systems to illuminate the Check Engine light - in my case, there was an Emissions System Not Ready OBD-II error.

There was an unofficial bulletin floating around but I came across a PIP (preliminary information post) from GM and the NHTSA. This bulletin specifies the first resolution for this issue is to replace the auxiliary transmission fluid pump control module (GM Part Number 24261817) and a couple of harnesses (24259589 and 24259590). There were some early reports that the control module was only available from a GM service center but it seems these are now available online as well. Parts & Labor this was a $637 fix and it seems to be working. Not sure how easy this replacement is for you DIYers.

If the control module is *not* this fix, then the next step is to replace the auxiliary transmission itself, which is about a $1200 fix.

The GM bulletin can be found at https://static.nhtsa.gov/odi/tsbs/2018/MC-10154554-9999.pdf
I have the same issue. And I changed out the parts that you mentioned above. A local mechanic is doing it. And he mentioned something about programming after he changed the parts. Have you heard of that before??
 

Nightskyisme

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Hi. I have been experiencing what has been called the "bump/jerk" on GMC hybrid trucks. The symptoms include a jerking sensation as the vehicle switches between hybrid mode and engine mode. This can also cause pauses in acceleration or also sudden accelerations at low speeds. This is typically accompanied by OBD-II codes P2797 (Auxiliary Transmission Fluid Pump Performance) and/or P0C2B (Auxilliary Transmission Fluid Pump Control Module Feedback Signal) and/or P0AC4 (Hybrid Powertrain Control Module Requested MIL). This may also cause other systems to illuminate the Check Engine light - in my case, there was an Emissions System Not Ready OBD-II error.

There was an unofficial bulletin floating around but I came across a PIP (preliminary information post) from GM and the NHTSA. This bulletin specifies the first resolution for this issue is to replace the auxiliary transmission fluid pump control module (GM Part Number 24261817) and a couple of harnesses (24259589 and 24259590). There were some early reports that the control module was only available from a GM service center but it seems these are now available online as well. Parts & Labor this was a $637 fix and it seems to be working. Not sure how easy this replacement is for you DIYers.

If the control module is *not* this fix, then the next step is to replace the auxiliary transmission itself, which is about a $1200 fix.

The GM bulletin can be found at https://static.nhtsa.gov/odi/tsbs/2018/MC-1015
 

Nightskyisme

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Hello, I am a new member and I have a 2009 Tahoe Hybrid that I purchased used in December, I do most of my own mechanical work and feel pretty well-versed although not entirely so with the hybrid system, the previous gentleman put in a new motor and new Hybrid battery in the vehicle just before I bought it, and it is in excellent shape, however I am getting this jerking sensation along with the POC2B code, I'm also getting the jerking sensation between Auto stop and start and found your post about this transmission pump issue, do you happen to know if this is something the dealer will do as a warranty or Goodwill repair, or something required under the National Highway Traffic Safety Federation? Or is this just an advisory technical service bulletin? If the dealer will do it under their expense, I will definitely bring it in, otherwise I will obtain the parts and do it myself I was just curious, thank you for this information!
 

BG1988

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Hello, I am a new member and I have a 2009 Tahoe Hybrid that I purchased used in December, I do most of my own mechanical work and feel pretty well-versed although not entirely so with the hybrid system, the previous gentleman put in a new motor and new Hybrid battery in the vehicle just before I bought it, and it is in excellent shape, however I am getting this jerking sensation along with the POC2B code, I'm also getting the jerking sensation between Auto stop and start and found your post about this transmission pump issue, do you happen to know if this is something the dealer will do as a warranty or Goodwill repair, or something required under the National Highway Traffic Safety Federation? Or is this just an advisory technical service bulletin? If the dealer will do it under their expense, I will definitely bring it in, otherwise I will obtain the parts and do it myself I was just curious, thank you for this information!
the computer is not getting feed back from the pump P0c2B Feed back signal out of bound
broken of corrosion on a wire or ground

check the Red white and blue wire it's just right inbetween the battery and fuse box to the left of the battery #10 wires it has like 6 or wires total


also check the transmission for backed out wires on the transmission harness (be careful they damage easy) it's a pretty common issue
 
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Nightskyisme

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the computer is not getting feed back from the pump P0c2B Feed back signal out of bound
broken of corrosion on a wire or ground

check the Red white and blue wire it's just right inbetween the battery and fuse box to the left of the battery #10 wires it has like 6 or wires total


also check the transmission for backed out wires on the transmission harness (be careful they damage easy) it's a pretty common issue
 

Nightskyisme

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Thank you! I was out there looking around tonight for those particular wires, I have two fuse boxes actually, there's the main fuse box, and there is a smaller secondary fuse box which has a lot of fan and pump relays in it, is this wire near or adjacent to this smaller fuse box? I was also looking for the auxiliary transmission control unit because somebody mentioned those wires may be corroded as well, and I see something with aluminum fins on it below this fuse box but I'm not sure where the wires are that attach to it because it looks rather crowded down there like I might have to remove this fuse box to get to it, either way, if you have a picture or diagram as to where these wires and or auxillary transmission control unit are located, that would be greatly appreciated, and the wires you are referring to on the transmission harness, is there only one bank of wires on the transmission that I need to be looking for? thank you!
 

BG1988

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Thank you! I was out there looking around tonight for those particular wires, I have two fuse boxes actually, there's the main fuse box, and there is a smaller secondary fuse box which has a lot of fan and pump relays in it, is this wire near or adjacent to this smaller fuse box? I was also looking for the auxiliary transmission control unit because somebody mentioned those wires may be corroded as well, and I see something with aluminum fins on it below this fuse box but I'm not sure where the wires are that attach to it because it looks rather crowded down there like I might have to remove this fuse box to get to it, either way, if you have a picture or diagram as to where these wires and or auxillary transmission control unit are located, that would be greatly appreciated, and the wires you are referring to on the transmission harness, is there only one bank of wires on the transmission that I need to be looking for? thank you!
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purple yellow blue red one that
are too the aux pump...


the ones too the transmission are a bundle if upto 16 wires... i think it's on the passenger side of the transmission
i believe it requires a special tool

see here



Dont for get to disconnect the 12v battery before messing with it20210806_184023 - Copy.jpg
 
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Nightskyisme

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Thank you, as it cools off this weekend I will get underneath and attempt to locate all of these connectors and cables, I believe the front drive shaft is in the way of most of this, but if I have to remove it I will, thank you again for your help I appreciate it very much as I try to locate this pesky issue!
 

BG1988

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Thank you, as it cools off this weekend I will get underneath and attempt to locate all of these connectors and cables, I believe the front drive shaft is in the way of most of this, but if I have to remove it I will, thank you again for your help I appreciate it very much as I try to locate this pesky issue!
it's the purple yellow blue red one that connects to the AUX transmission pump i made a mistake
 

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