[mr_udy]

My '02 8.1L w/ 36k on it just developed a driveability problem.

Apears to want to stall when slowing to a stop (rpms go below 500) and sometimes feels like transmision isnt downshifting causing the truck to sorta want to keep pushing forward for a brief second.

Truck accelerates fine unless coming off of the stumble where it feels like a sudden acceleration from the brief delay.

Truck idles fine when in nuetral or park (no load).

Woried that it was a tranny problem....but fluid level is correct and looks good-red. I dont believe its been serviced yet...could a spin on filter replacement fix whatever is going on? Thought I may have read a while ago that that can cause driveability problems....

Problem apears to occure when warmed up...but cold out. Might be coincidence as it just started getting cold around here.

Does this sound like the infamous 8.1L crank sensor issue?

I'm gonna post similar message in Allison OEM in case its a tranny problem.

 

[Scott2500hd]

Document ID# 880188
2002 Chevrolet Chevy K Silverado - 4WD

Subject:Harsh or Delayed 2-1 Downshift, Neutral Feel at a Stop, Shift Busyness, DTCs P0708, P0847, P0872, P0875, P1711, P1713 (Reprogram TCM) #02-07-30-020 - (04/22/2002)


Models:2001-02 Chevrolet and GMC C/K 2500/3500 (3/4 and 1 Ton) Series Pickup Models (Silverado and Sierra)
with Allison® Series 1000 Automatic Transmission (RPO M74)​

<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=880188&pubid=271#ss1-880188">Condition

Some customers may comment on a harsh or delayed 2-1 downshift, a neutral feel at a stop or shift busyness (excessive shifting). Upon investigation, the technician may also find one or more of the following DTCs set:

• P0708
• P0847
• P0872
• P0875
• P1711
• P1713​

<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=880188&pubid=271#ss2-880188">Correction

Reprogram the Transmission Control Module (TCM) with the new service calibrations which were available from Techline starting March 24, 2002 on the TIS2000 version 3.5 or later. These calibrations are electronic calibrations and are NOT available from GMSPO.
These new calibrations will address the following conditions:
2001
2002
Delayed 2-1 downshift at a stop
2-1 downshift quality concerns
Flare & bump on low speed coast-down and throttle reapply
Cold shift quality concerns
2-1 closed throttle neutral feel
*Shift busyness
Harsh 2-1 downshift
DTC P0708, P0847, P0872, P0875, P1711, P1713
Shift busyness
2-1 closed throttle neutral feel

*Important: 2002 Vehicles with 8.1L Engine --
If the concern is shift busyness, the PCM must also be reflashed to gain maximum benefit from the new TCM service calibration. This calibration was available from Techline starting March 10, 2002 on the TIS2000 version 3.0 or later. If the concern is not shift busyness, this step is not required.


This additional step is not required on vehicles with a 6.6L diesel engine (RPO LB7) or 2001 vehicles with an 8.1L engine (RPO L18).


<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=880188&pubid=271#ss3-880188">Warranty Information

For vehicles repaired under warranty, use:
Labor Operation
Description
Labor Time
K5364
Module, Transmission Control - Reprogram
0.4 hr
J6355
Powertrain Controller -- Reprogram
0.4 hr


GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION

© Copyright General Motors Corporation. All Rights Reserved. ​

Does this help????

 

[mr_udy]

Damn dude! Thanks....whata I owe ya? :bow:

Sounds exactly what I am experiencing. Only had truck since october so kinda wondering why it reared its ugly head now. Hope it has nothing to do with my 285s I put on a few weeks ago...

I wonder how much dealer will charge for this.....anyone have it done?

 

[mr_udy]

whoops....just saw .4hrs....thanks again

 

[Scott2500hd]

Tire size can do some funny things with the Allison. The TCM will likley have to relearn after the software change. It may be better after the update.

I used to have an 2003 8.1 and even 265's gave me a little funky shift.

 

[Scott2500hd]

Heres a little info on bigger tires.

Document ID# 1884523
2002 Chevrolet Chevy K Silverado - 4WD

Subject:Info - Inspection of Tire and Wheel Size Prior to Diagnosis of Transmission Shifts, Poor Performance, Speedometer, Cruise Control Concerns #01-03-10-010F - (01/04/2007)


Models:2001-2007 Chevrolet Silverado Pickup (Classic) Models
2001-2007 GMC Sierra Pickup (Classic) Models
with Allison® Automatic Transmission​

This bulletin is being revised to add the 2007 model year. Please discard Corporate Bulletin Number 01-03-10-010E (Section 03 -- Suspension).
Proper diagnosis of engine, transmission, speedometer and cruise control concerns must begin with an inspection of tire/wheel size.

• The 2500 series trucks have LT245/75R16E tires as standard equipment.
• The 3500 series trucks with dual rear wheels have LT215/85R16D tires as standard equipment.
• The 3500 series trucks with single rear wheels have LT265/75R16E tires as standard equipment.​

A truck that has different tires and wheels will have engine power/performance concerns, transmission shift concerns, speedometer registered speed concerns, cruise control concerns and increased steering effort, especially during parking lot maneuvers at slow speeds.
Before any diagnosis is performed for these types of concerns, inspect the tires/wheels for the proper tire and wheel combinations.
If a truck is found to have other than the above listed tire sizes, no further diagnosis should be undertaken until the original size tires and wheels are reinstalled on the truck.
The Engine Control Unit (ECM) and Transmission Control Module (TCM) use (RPM) and (VSS) inputs as operational parameters for engine torque, transmission shifting, cruise control operation and speedometer indicated vehicle speed.
Calibrations for different tire/wheel combinations are not available.
Therefore, changing of tire and/or wheel size should not be undertaken by dealerships or truck owners.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1884523&psdid=271&evc=sm#ss1-1884523">Warranty Information

Reinstalling the proper wheels and tires on the vehicle, prior to performing any type of diagnosis of the truck, would be considered truck owner responsibility and not a warranty repair.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION

© Copyright General Motors Corporation. All Rights Reserved. ​

 

[Scott2500hd]

Sorry if I am giving you too much info....its slow here today....


Document ID# 1218726
2002 Chevrolet Chevy K Silverado - 4WD
FastLearn Procedure

<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1218726&evc=sm&pubid=271&cellId=118157&mspsdsubkey=1991#ss1-1218726">Overview

In general, FastLearn is a procedure for Allison 1000 Series transmissions in which a series of tests are run to allow the transmission control module (TCM) to learn individual clutch characteristics. Once the clutch data is learned, FastLearn translates it to the adaptive data cells, which the TCM uses for clutch control during range shifts. FastLearn is used at GM assembly plants, and allows the vehicle to be driven out of the assembly plant in a near-fully-adapted state so as to minimize any customer shift concerns. The scan tool version of FastLearn is intended to provide the same benefit following transmission repair or replacement at GM Dealerships.
FastLearn must be used when one of the following repairs have been made to the vehicle:

• Transmission replacement or internal service/overhaul
• Valve body repair or replacement, including replacement of the pressure control solenoid A or the pressure control solenoid B
• TCM replacement
• TCM software/calibration update
• Any service in response to a shift quality concern​

The scan tool is used to initiate FastLearn by selecting the following commands:

• F3: Special Functions
• F1: Transmission Output Controls
• FastLearn​

Important: When performing FastLearn, the following conditions must be met:

• Block the drive wheels.
• Apply the parking brake.
• Apply the service brake during DRIVE and REVERSE.
• 0 percent throttle and engine at idle RPM
• Transmission sump temperature is between 40-100°C (104-212°F) - Ref temp bargraph on screen.
• If equipped, 4WD transfer case in 2WD​

Important: If at any time during the procedure, required conditions are not met, FastLearn may abort and the process will need to be started again from the beginning.

Four steps are required to successfully complete the FastLearn procedure:

1. <LI type=1>PARK Mode <LI type=1>DRIVE Mode <LI type=1>REVERSE Mode
2. 4-5 Clutch Learn Mode

<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1218726&evc=sm&pubid=271&cellId=118157&mspsdsubkey=1991#ss2-1218726">PARK Mode

While the transmission is in PARK, with the engine idling, FastLearn will cycle through a series of tests where the 3rd, 5th and reverse clutch and the 2nd clutch is repeatedly applied to learn their clutch characteristics. During the 3rd, 5th and reverse clutch and 2nd clutch apply/release procedure, FastLearn is able to characterize the pressure control (PC) solenoid A and PC solenoid B pressures corresponding to clutch return springs, and is also able to learn the volumes for the 3rd, 5th and reverse clutch and 2nd clutch packs. In addition, the low and reverse clutch is repeatedly applied and released in PARK to purge out air for later learning of the clutch volume.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1218726&evc=sm&pubid=271&cellId=118157&mspsdsubkey=1991#ss3-1218726">DRIVE Mode

Caution: Block the wheels before selecting DRIVE. While in DRIVE, if the Scan Tool loses communication or becomes disconnected, the vehicle could move forward. Failure to block the wheels could result in personal injury or property damage.
Once all of the PARK test data have converged, the scan tool instructs the driver to select DRIVE. Once DRIVE is selected, the TCM engages the 1-2-3-4 clutch to obtain DRIVE and learn 1-2-3-4 clutch volume. The TCM repeats this test until the volume learned for the 1-2-3-4 clutch has converged.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1218726&evc=sm&pubid=271&cellId=118157&mspsdsubkey=1991#ss4-1218726">REVERSE Mode

Caution: Block the wheels before selecting REVERSE. While in REVERSE, if the Scan Tool loses communication or becomes disconnected, the vehicle could move backward. Failure to block the wheels could result in personal injury or property damage.
Next, the scan tool instructs the driver to select REVERSE. Once REVERSE is selected, the TCM engages the low and reverse clutch to obtain REVERSE and to learn the low and reverse clutch volume. The TCM repeats this test until the volume learned for the low and reverse clutch has converged.
Important: All shifts will be left in fast adaptive mode at this point.

After learning the 1-2-3-4 and the low and reverse clutch volume, FastLearn updates the adaptive volume data for all shifts, with either the 1-2-3-4 or the low and reverse on-coming clutch. This completes the stationary modes of FastLearn.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1218726&evc=sm&pubid=271&cellId=118157&mspsdsubkey=1991#ss5-1218726">4-5 Clutch Learn Mode

Important: The technician should verify that transmission shift quality for all types of shifts is acceptable prior to releasing the vehicle to the customer.

Following the REVERSE Mode step, the scan tool exits FastLearn, and the only adaptive cells that remain to be learned are the adaptive volume data for the 4-5 clutch. The vehicle must be driven in order to make at least three 3-4 upshifts on the same ignition cycle and at steady throttle position. This data is learned by the TCM intentionally overfilling the 4-5 clutch. Once this overfill is corrected, the 4-5 clutch volume is learned and all special FastLearn actions are completely disabled.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1218726&evc=sm&pubid=271&cellId=118157&mspsdsubkey=1991#ss6-1218726">Troubleshooting

If FastLearn will not run and the above stated conditions have been met, ensure the following:

• Transmission fluid temperature is between 40-100°C (104-212°F).
• Closed throttle and engine at warm idle RPM
• No active DTCs.
• All speed sensors are connected and functioning properly.
• Park/Neutral position switch is properly adjusted and functioning.
• Main pressure is within specification.
• TCC slip speed less than 100 RPM at idle in PARK/NEUTRAL​

 

[CADTECHTOM]

.4 is warranty time to reprogram the pcm. If you are out of warranty your looking at 1 hour labor. But it sounds more like a crank sensor problem to me, and a dealer will probably charge you 2 hours to replace it. Just a guess, but 90% of 8.1 stalling i see is crank sensor related. Good luck

 

[Scott2500hd]

I must of missed where it stated stalling in the original post....

 

[mr_udy]

nah..I think your right. I never actually stalled...sorta felt like it was gonna. I think you hit the nail on the head!

Not sure what to do now since it apears I cant have it reflashed with 285s....or can I? Will it simply relearn speed/rpm relationship if I have it reflashed with the bigger tires? I did have it recalled for 265s when I upgraded to those....ran fine...probably cause computer understood speed and rpm relationship. Now, from what your info said, I bet I am having a problem with speed and rpm different.

Also, this only really seems to happen the last couple days...coincidentally with the plow on. I wonder if it'll sorta go away once the added strain of plow is off....dont understand why that would matter but its worth a try. Maybe additional tire squish from weight of plow doing something...front and rear "rotations" not the same?

I wonder if its simply an annoyance or am I causing damage? If its an anoyance, esspecially if truly only with plow, I can live with it. I dont want to do any damage to expensive tranny though!

 

[ockgator]

For the near stall try cleaning out the throttle bore, use an old toothbrush and some throttle bore cleaner, do it key off as the throttle motor is a strong puppy

 

[mvnvltn]

For the near stall try cleaning out the throttle bore, use an old toothbrush and some throttle bore cleaner

:agreed:

 

[Blk04HD]

I never had any weird shifting problems with my 8.1 and allison with 265s or 285s.

 

[Chevy2500HD8.1]

when my crank position sensor started acting up, it never did actually stall. When I would roll up to a stop sign or light as I got down to about 5 mph or less it would start to run very ruff, and almost stall, but never did. Replaced the sensor, relearned it and never had a problem since. That was last summer.

 

[billcar9999]

Most people with the crank sensor issue complain about random stalling. That's what mine did. I also had the problem you describe. It required the TCM software to fix it. The message below describes what is happening. I snagged it from another post a long time ago. I don't remember where or I'd give credit.

What was happening is as you came to a rolling stop that the range selected, range attained and range commanded was being observed. When the trans made the down shift, the range commanded by the transmission computer was neutral and then came back to first range thus you felt the several second time lag when the unit came back to range.

 

[mr_udy]

bilcar99: What size tire are you running? What year truck?

Thanks all for your help...I'll post what I find.

I am leaning towards the recallibration. BUT, I'm gonna clean my TB anyway...my old mechanical one on 5.3s always "coked" up...free service. Since I have'nt stalled yet, gonna save the crank sensor for last. By the way, where is the crank sensor? Front? Easy replacement?

 

[billcar9999]

bilcar99: What size tire are you running? What year truck?

Thanks all for your help...I'll post what I find.

I am leaning towards the recallibration. BUT, I'm gonna clean my TB anyway...my old mechanical one on 5.3s always "coked" up...free service. Since I have'nt stalled yet, gonna save the crank sensor for last. By the way, where is the crank sensor? Front? Easy replacement?

I have 285's on it and it's a 2001. The crank sensor is on the back of the block, drivers side. It's a PIA to get out. It took me about 2 hours to finish it.

 

[Manic Mechanic]

The crank sensor is behind the drivers side cylinder head, going down behind the block inside the transmission bell-housing. It can be done by a competent do-it yourselfer on a cool engine within an hour taking your time to be careful. All '01's and early '02's need it. The replacements are a new design.

I'm glad Scott posted the TSB on the Allison reflash because my '01 has had this exact problem since new. I have Mitchell On Demand and they don't list that TSB at all, $150 a month for what? Maybe it's too new to be listed, I looked again last night. Anyways I called my dealer Friday and was quoted $80 to reflash the TCM with this update. Tire size changes will prevent the dealer from deciding if you need it but won't prevent the fix from working should you have it done. My tire size (265) has been corrected by a Hypertech in the PCM anyways and they won't be changine that to reflash the TCM. (TCM = transmission control module which is an auxillary computer, PCM = powertrain control module which is the main computer.)

I had to replace my crankshaft sensor not long after I purchased my truck and it is a completely different problem so perhaps I can explain the difference. With a failing CKS POS your ignition timing will be off a little and every once in a while it will drop a signal and the engine just shutters or stalls. As it gets worse it will take longer and longer to restart. It has to get really bad to set a code, but mine had a "pending code" after the first stall. You won't notice the timing difference until you have it fixed and it runs crisper and gets better mileage. It had little if any effect on shifting.

With the transmission shifting problem the main thing I notice is that when I come to a stop, especially when it's cold still, if I don't stop completely for at least a full second, when I step on the accelerator the engine revs a couple of hundred RPM like it's in neutral then grabs first hard and goes. It's harsh and annoying. Same thing some times if I roll down to a low enough speed to get back into first gear in slow traffic. People I've had in the truck for the first time have commented on it, I've assumed and told them that's the price you pay for having such a heavy duty transmission. Now I find out it can be fixed. As far as shift busyness goes I won't know the difference until it's done. My truck is the only 8.1/Allison I've spent much time in. The customers I have with them (2) have only been oil change types so far. A new guy showed up last week with an '03 and will be in soon for a tune-up so one way or another I'll see a comparison.

But as annoying as the problem is I'll gladly spend the $80 to have it addressed. This price may be due to it's one professional shop doing work for another and not include walk in customer charges. (I told them what I wanted done, without any diagnostic or follow up charges etc.)

Vernon

 

[GMCWAYNE]

"All '01's and early '02's need it."
My 02 was manufactured in 5/06/2002. Does this mean that I'll be in the clear for the crank sensor problem? I've got 37k miles on it now and so far no issues with stalling.

 

[Manic Mechanic]

GMCWAYNE, call your local dealer's service dept. and have them run your VIN to see if you have the old or new design crank sensor. That's the only way to tell without taking it out to look at it without knowing exactly the day they switched.

Vernon