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Old 02-19-2009, 10:02 PM   #1 (permalink)
jdelling
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GM Fix for Allison Harsh Downshift

Hello All,

I have a 2006 LLY with Allison I brought it to the dealer becuse the tranny would lockup going form 2-1 gears. I found this Closed thread about this problem I'm having...
Hard Down Shift while stopping.


So anyways, I printed out the thread posts above to describe my problem and gave it to the dealer to say I'm not the only person having this problem. I can't reproduce the problem but lucky for me it locked up on the GM tech during his test drive so after they looked at it for 3 days...
They replaced the sensor. I'll let you know if the problem occurs again.

GM Document ID: 1982002:

#PIP 4144: Allison LCT1000 Harsh 3-2 2-1 Downshift and ABS may Activate - Keywords cold hard shift- (Jun 4, 2007)

Models:
2001-2007 Chevy/GMC Silverado Classic
2007 Chevy/GMC Silverado

Condition:
The Allison LCT1000 transmission combined with 8.1 (L18) or 6.6L (LB7/LLY/LBZ/LMM engine may experience ABS activation during a harsh 3-2 or2-1 downshift and or harsh garage shifts.
May experience delay or "Hanging" upshifts when not using Tow/Haul. The coolant temperature gauge in the IPC may read cold. The engine Coolant Temperature Sensor (ECT) may be reading cold (approximately 15.5 degrees C (60 degrees F) or may be reading erratic when the engine is at full operating temperture.

Recommend:
The ECT sensor should be monitored with the TechII Scan Tool and replaced as needed.

Last edited by jdelling; 02-19-2009 at 10:05 PM.
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Old 02-24-2009, 09:41 AM   #2 (permalink)
Taxx
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Your on the right track. The 2-1 downshift is very "sensitive" when it comes to the input and output speeds.

Please keep us posted.
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Old 03-02-2009, 10:21 AM   #3 (permalink)
jdelling
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So far so good.....I think its fixed!
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Old 03-06-2009, 02:15 AM   #4 (permalink)
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Quote:
Originally Posted by jdelling View Post
Hello All,

I have a 2006 LLY with Allison I brought it to the dealer becuse the tranny would lockup going form 2-1 gears. I found this Closed thread about this problem I'm having...
Hard Down Shift while stopping.


So anyways, I printed out the thread posts above to describe my problem and gave it to the dealer to say I'm not the only person having this problem. I can't reproduce the problem but lucky for me it locked up on the GM tech during his test drive so after they looked at it for 3 days...
They replaced the sensor. I'll let you know if the problem occurs again.

GM Document ID: 1982002:

#PIP 4144: Allison LCT1000 Harsh 3-2 2-1 Downshift and ABS may Activate - Keywords cold hard shift- (Jun 4, 2007)

Models:
2001-2007 Chevy/GMC Silverado Classic
2007 Chevy/GMC Silverado

Condition:
The Allison LCT1000 transmission combined with 8.1 (L18) or 6.6L (LB7/LLY/LBZ/LMM engine may experience ABS activation during a harsh 3-2 or2-1 downshift and or harsh garage shifts.
May experience delay or "Hanging" upshifts when not using Tow/Haul. The coolant temperature gauge in the IPC may read cold. The engine Coolant Temperature Sensor (ECT) may be reading cold (approximately 15.5 degrees C (60 degrees F) or may be reading erratic when the engine is at full operating temperture.

Recommend:
The ECT sensor should be monitored with the TechII Scan Tool and replaced as needed.

my tranny has done the same thing several times in the past few months. It really feels like I was hit from behind as others said. Seems like it happens to me when I'm in traffic and right when I reach the speed where the tranny goes to shift to 2nd and I have to hit the brakes.. causes the tranny to kinda jam back into first. It actually locked up the rear tires one time.

Anyway.. just wondering what the "stealer" will charge me to replace the ECT sensor. I'm over mileage for warranty coverage.
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Old 03-06-2009, 02:34 AM   #5 (permalink)
DURAtotheMAX
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thats really wierd. I wonder why would the coolant temp sensor affect those things? Since when does the trans care how hot the engine is? The only thing that affects it is TRANNY fluid temp... :
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Old 09-13-2010, 05:34 PM   #6 (permalink)
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Any body have any new data on this... This is exactly what is happening to my newly rebuilt transmission.... I've got metal in my trans fluid with roughly 1,000 miles since the build, probably jsut totally ****ed my new trans. this has happend to me I'd say 5 times since the build and a few times before the build. I saw on another site Horsehaulin thought it was the rear speed sensor IIRC.
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Old 09-13-2010, 05:53 PM   #7 (permalink)
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Mine has always had a bump when shifting from 2nd to 1st when cold but goes away when warms up I just figured it was the nature of the beast
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Old 09-18-2010, 10:58 AM   #8 (permalink)
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Does anyone know where this The ECT sensor is located ?
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Old 09-18-2010, 12:37 PM   #9 (permalink)
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It's just a little to the left and rear of the oil fill cap, right next to your alternator. Since it's a coolant temp sensor, it's obviously on the coolant line path.
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Old 09-18-2010, 04:31 PM   #10 (permalink)
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Quote:
Originally Posted by KEVINL View Post
Mine has always had a bump when shifting from 2nd to 1st when cold but goes away when warms up I just figured it was the nature of the beast
Mine does that from time to time, but I assumed the same thing.
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