Service bulletin for hybrid bump/jerk issue

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ChuckC

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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
 

lt1gmc

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On my 09, I found the fix to be unplugging the trans pump/trans pump module connectors just under the battery and replugging them in. The high current overheats one of the pins and causes a bad connection. Did this a few times over 15,000 miles until I cleaned the connectors real good and didn't have an issue since. They updated the module and pump in 2010 and one of the changes was the plugs.
 

BG1988

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On my 09, I found the fix to be unplugging the trans pump/trans pump module connectors just under the battery and replugging them in. The high current overheats one of the pins and causes a bad connection. Did this a few times over 15,000 miles until I cleaned the connectors real good and didn't have an issue since. They updated the module and pump in 2010 and one of the changes was the plugs.
pics of the location would be way more helpful :) do i have to remove the whole battery?
 

lt1gmc

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pics of the location would be way more helpful :) do i have to remove the whole battery?
Sorry the truck is not nearby right now but you do not have to remove the battery. The two connectors are below the box just down and to the right (looking from drivers seat) of the battery. Only connectors in the area, the ones with the slightly larger wires is the one.
 

BG1988

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Sorry the truck is not nearby right now but you do not have to remove the battery. The two connectors are below the box just down and to the right (looking from drivers seat) of the battery. Only connectors in the area, the ones with the slightly larger wires is the one.
do i have to disconnect the battery i.e HV or 12v(i know disconnecting this would be a good idea)
 

lt1gmc

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do i have to disconnect the battery i.e HV or 12v(i know disconnecting this would be a good idea)
No need to disconnect either battery, just the connectors, with the engine off of course.
 

BG1988

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No need to disconnect either battery, just the connectors, with the engine off of course.
i'll check it out tomorrow I have electrical cleaner and a toothbrush
 

BG1988

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No need to disconnect either battery, just the connectors, with the engine off of course.
ok i think this is the connection?? I resat the connect there appears to be no Heat damage to the connection...20210203_121137.jpg 20210203_121419.jpg
 
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lt1gmc

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I was referring to the 12 volt battery under the hood. just to the passenger side of the battery and under a black control box is a couple of connectors with wires leading down the driver side of the engine, one with some larger wires in it, maybe 3 or so. Disconnect both of these connectors and replug back in to see if that corrects the problem. Pics below are from a 13 but give an idea of the area of the connectors.

Hybrid Conn 1.jpg Hybrid 2.jpg
 
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BG1988

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but it is weird that me cleaning the other connection helped? only 3 out 20 resumes had only a minor "lag"


compared almost every start resume "lagged" pretty much... some sorta placebo effect?



edit (Yeah it was a placebo effect) as that "effect wore off"


before I used to manually start the engine by putting it in M4


so it's the positive battery cable? i have a brand new one in my storage area that is ready to put in(both neg and pos cables)


it's the one with the Yellow, purple and red wire?
 
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