Allison 1000 Problem After Fluid Change

[Oemtech]

This the 2nd fluid change for me. I changed fro Dexx III to Mobil Synthetic and never had a problem.

But this time I decided to change to TranSynd. I picked up 3 gals of TranSynd, plus 1 qt and a new Allison filter.

1) Drain out the old fluid
2) Install new filter that I fill the filter with fresh TranSynd
3) Added 12 qts of TranSynd
4) Start the engine and check the fluid level - ok at the cold mark.

Now comes the weird part. I was getting ready for a short RV club trip and pulled the rig out of the RV barn and parked it on the road. I left the engine run so I could check the trans after it warmed up. I hooked up the toad, losed up the RV barn and got ready to go.

1) I put it Drive and headed out. But it didn't feel right.
2) About 1/4 mile down the road it did not shift.
3) I stopped and put it Park. I then checked Reverse ... No Reverse. I checked the other gears and all I had was Drive. It seemed to be locked in 1 gear. I also shut it off and tried again with the same results.
4) Being that I was on a 2 lane county road I had to drive about 2 miles to get the rig back to the RV barn.
5) When I got to the first turn I decided to put it Park and shut it off again. I let it set for a minute or so and restarted to test. Wa La all gears work.

What really bugs me is this is the 2nd time this has happened after a fluid change. It happened once before to a customers RV. But, in that case I had done an UltraPower upgrade. I actually remove the UP upgrade and it didn't make a difference. So we took the rig back to the shop to check things out. Needles to say I reinstalled UltraPower and went for a test drive and it worked like a charm. Now that I think about it, my symptoms were the same as the first time. Both worked normally after 2 cycles of the ignition switch. Is this a built-in Allison reset?

[sknight]

Never had that happen after a fluid change but the protocol could be different in an RV application.

Allison was extremely touchy about things being just so so, we had a truck have it's warranty locked out over a tire size change from 245 to 265 which were off of a stock truck with a 4L80E.

Yours went into a failsafe condition, quite possibly because it didn't detect "X" pressure in a given amount of time. Even filling the filter there's a bit of air to purge out. GM/Allison programming will failsafe for some screwy reasons. One of the most indestructible transmissions built but it can be the most sensitive regarding the electronics. I'm sure you've heard of the Allison only PRNDL switch issues.

Besides it's a GM product. They're partners with Microsoft. If something doesn't work, repeat the procedure and expect a different result!

[Oemtech]

Originally Posted by sknight

I'm sure you've heard of the Allison only PRNDL switch issues.

Besides it's a GM product. They're partners with Microsoft. If something doesn't work, repeat the procedure and expect a different result!

PRNDL problem... Please enlighten me.

MS/GM.... Hummmm I guess I must have done ctrl-alt delete Allison style to fix it.

[sknight]

Might not have been a medium duty issue. On the Allison 1000 equipped light trucks the PRNDL switches would get water in them and cause all sorts of shifting problems. Physically and visually they're no different than the 4L80 or even the 4L60 switch, I think the TCM was so sensitive it would pick up water getting across the contacts confusing what range it was supposed to be in. The new ones were sealed better, had a shield, etc.

Here's what a google search turned up. Wish I still had GM access.

#02-07-30-011C: Slow or No Engagement of Automatic Transmission, No Start, Blank PRNDL Display, Flashing PRNDL, DTC P0708, P0872, P0847, P0875, P1711, P1713 or U1000 Set (Diagnose Condition, Repair) - (Jun 21, 2004)

Subject:Slow or No Engagement of Automatic Transmission, No Start, Blank PRNDL Display, Flashing PRNDL, DTC P0708, P0872, P0847, P0875, P1711, P1713 or U1000 Set (Diagnose Condition, Repair According to Procedure)

Models:2001-2004 Chevrolet Silverado
2001-2004 GMC Sierra
with Allison® LCT1000 Automatic Transmission (RPO M74) and
6.6L Duramax™ Diesel Engine (RPO LB7) or 8.1L Gas Engine (RPO L18)

This bulletin is being revised to add model years and additional model information and add graphics. Please discard Corporate Bulletin Number 02-07-30-011B (Section 07 -- Transmission/Transaxle).
Condition

Some customers may comment on one or more of the following conditions.
• The PRNDL display is flashing.
• The engine will not start.
• The "Service Engine Soon" Indicator lamp is illuminated.
• The transmission does not shift properly.
• The vehicle will not move, transmission will not engage.
Cause

Moisture contamination within the Park Neutral Position (PNP) Switch may cause this condition. This is sometimes referred to as the Neutral Start Back-up (NSBU) Switch. On a left turn, water spray from the left front tire is directed directly at this switch. Proper installation of the "Front Shield" and "Rear Shield" are essential for proper repairs.
Technician Diagnosis

Object Number: 1523662 Size: SH
Click here for detailed picture of above image.

This bulletin ONLY applies to vehicles equipped with a two connector PNP switch as shown above.

A complete and through diagnosis must be performed by a qualified electrical technician to determine the cause and avoid needless replacement of good components.

Important: The Transmission Control Module (TCM) and or the Pressure Switch Manifold (PSM) should NOT be replaced unless properly diagnosed. They are probably not the cause of the concern. It is often assumed the module is the cause of the concern when, in fact, it is another component or the wiring between the components that causes the concern.

Important: Remember, everything starts with a properly operating Neutral Start Back Up (NSBU) switch. The NSBU switch has been incorporated into what is now called the Park Neutral Position (PNP) switch. If the PNP switch does not provide the proper voltage signal to the module indicating the transmission is in either Park or Neutral, the module will not allow the starter operation. After the engine is started, and the shift lever is moved to either Reverse or one of the drive positions, the range selected portion of the PNP switch portion provides a voltage input to the module as to what range the driver has manually selected for transmission operation. The module then controls pressures, shift points and other transmission functions based on the voltage input received from the range portion of the PNP switch.

The technician may find one or more of the following conditions. The list of these conditions does not imply any type of frequency or order. They are random events and may occur in any order.
• DTC P0708, Neutral start/backup (PNP or NSBU) switch
• DTC P0847, Pressure Switch Manifold (PSM)
• DTC P0872, Pressure Switch Manifold (PSM)
• DTC P0875, Pressure Switch Manifold (PSM)
• DTC P1711, Pressure Switch Manifold (PSM)
• DTC P1713, Pressure Switch Manifold (PSM)
• DTC U1000, Serial Data Communications
• Blank PRNDL Display
• Flashing PRNDL Display
• Slow or No Engagement of Automatic Transmission
Blank PRNDL Display

A blank PRNDL display may indicate a condition with the PNP switch and/or one or more of the four signal circuits from the PNP to the TCM.

1. Pin A, Circuit 771 (BLK/WHT)
2. Pin B, Circuit 773 (GRA)
3. Pin C, Circuit 776 (WHT)
4. Pin D, Circuit 772 (YEL)

Or, a blank PRNDL display may also occur if an out of line condition exists with the Serial Data Circuit (CKT 2470, yellow wire) from the TCM to Splice Pack 205.
Diagnostic Tip

[Oemtech]

Very interesting... so far I have not heard anyone on Workhorse chassis having that kind of problem.

[Hooligan]

Also applied to motorhomes..and 1000/2000 series trans.
In 2002 Allison initiated a Customer Satisfaction Campaign (2002C1) to replace the NSBU switch and re-calibrate the TCM on my motorhome. (Allison 1000, Cummins ISB.)
"Some NSBU switches may experience intermittant or continuous diagnostic codes at a frequency unacceptable to Allison Transmission and it's customers. These codes are a result of internal corrosion due to water and salt intrusion affecting the TCM, resulting in inhibited transmission shifts." --This service replaces the NSBU with an improved design switch and a shield kit.
The replacement was initiated by Allison, I had not had any indications of a problem..

[Twinsberry]

I wish that I knew this 4 weeks ago. My driveshaft broke and busted the cooling lines and case on the transmission. Had everything repaired and drove about 150 miles before the RV started missing and not shifting properly. No codes or warning lights. Had Allison dealer check trans no codes and advised low enging power (Cummins ISB). Had Cummins check and found pickup pump bad. Great news I thought but we had the same problem with the transmission not changing gears unless we were going down hill. Mobile truck serviced the trans and finds through the computer that the transmission was low on fluid even though the dip stick says full. I asked how am I to know the level is the dipstick is incorrect. I don't have a answer yet on that one. But everything is fine now. Going to take her on a short trip over the weekend, then a long one through the mountains for Labor Day. What a long summer with no RV.