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Discussion Starter #1
The truck in my sig below is stuck.
DIC says "Shift Range Inhibited".
Shift lever moves freely, but little "-" under gears is flashing.
Before everybody jumps on, I've searched, but the codes I'm seeing don't seem to align with what I'm seeing on my Edge CTS.
I'm seeing:
P0463
P1093
U1026
U1041
Thanks in advance for any guidance you might provide.
 

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I’m gonna go for the nsbu switch right off the bat


2004 Silverado Cali lb7, Airdog ll 165, fresh sticks at 325k, Rick Fletes Dsp 5 on v2, 33x12.5 nitto at on 20 inch American Racing 20x10 wheels, Stage 5 Built Transmission by Mike Cole with triple disc billet low stall converter, 4 inch Injen cold air intake, Profab Intake Horn, Batmo Wheel, PPE Race Valve, Full EGR Removed w/ fed belt, 3.5 inch MBRP Downpipe, Full five inch MBRP Exhaust axle dump, lbz cp3 pump, Dual Platinum AGM Duralast, High Output Alternator, Cognito Pittman and idler w/ support kit, Cognito Upper Contol arms, Drilled and Slotted Rotors on all four Corners, FED Y Bridge, Shantz Custom Fab Traction Bars.
 

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Discussion Starter #3
Swapped NSBU and no improvement.
Swapped the ignition switch no improvement.
During first week dealer had it they swapped fluid pressure switch and no improvement.
Now they suspect bad ecm after three weeks. If they are right, I lose my tunes and FYI, Fleece doesn't keep backups ��
Could it be ecm?
 

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First, you need a better code reader than an Edge CTS to get all the TCM codes. It only does basic ODBII codes, and any codes from the transmission are things that effect emissions.

Second, the dealer should have the FSM, and not just be throwing parts at it. There's a fairly detailed checklist to go through for pretty much EVERY code the truck can generate.

The TCM would be ahead of the ECM on my list of things that cause "range shift inhibited".
 

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Discussion Starter #5 (Edited)
Here are the things done so far in the order I know

1. NSBU switch
2. Ignition switch
3. Fluid pressure switch
4. Internal harness
5. Ecm
6. Said they were trying Tcm next
But so far still no action turning the driveshaft
Everyone seems convinced it is electrical related though.
:confuzeld

Oh everything after 2 done at Chevy dealer who I believe uses a Tech 2 if I read it right.
 

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did they actually hook it up and check for codes? It sounds like they are just throwing parts at your truck.
 

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Discussion Starter #7
It has no codes. Dealer called today. They are stumped. They did say that they did not try ECM due to $2k cost. They are ready to start throwing parts at it. I could sure use some advice. They are able to see action in valve body when commanded from scanner manually. They even tried a second NSBU switch.
 

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With just the DIC message, but no codes, I would suggest getting them to phone GM for what should be done. I looked through the '04 FSM, and couldn't find anything for the DIC message. They just had some stuff if the indicator for the current shift mode was missing or flashing.
 

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Discussion Starter #9
Nick @ Merchants is trying to help. He has asked me to reach out and ask dealer to unplug tranny and see if we have reverse and third. If so, if I understand him correctly it points toward an electrical issue. If not, apparently it appears towards something perhaps hydraulically-oriented inside the tranny.

If also pm'd Mike L but haven't heard back from him yet. I respect these guys' knowledge and expertise and hope one of them might have an idea.
 

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Nick @ Merchants is trying to help.
I live by and Merchant is just an internet parts seller, they don’t work on trucks.

Shift range inhibited occurs when the input shaft is still turning at a standstill. (No geartrain pull down) The TCM will not command a gear unless the clutches that should be released are not, and the clutches that need to apply are not applied.
Low fluid, restricted sump filter, clutch damage, and weak trim solenoid and sticky E shift valve can cause this. Low voltage can also have an effect. The Allison needs 12.6 volts to operate properly. Anything lower than 11.5 volts may cause it to act up.

When the Dealer Unplugged the main harness from the trans, was it full of trans fluid?
Why hasn’t no one addressed your codes?
DTE P0463
Circuit Description

The fuel level sender changes resistance based on fuel level. The PCM monitors the signal circuit of the fuel level sender in order to determine fuel level. When the fuel tank is full, the sender resistance is high and the PCM senses a high signal voltage. When the fuel tank is empty, the sender resistance is low and the PCM senses a low signal voltage. The PCM uses the signal circuit of the fuel level sender in order to calculate the total remaining fuel (%) in the tank. The PCM sends the fuel level percent via the class 2 serial data circuit to the instrument cluster in order to control the fuel gauge. The fuel level information is also used for misfire and EVAP diagnostics.
Conditions for Running the DTC

The ignition is ON.
Conditions for Setting the DTC

• The fuel level signal is greater than 98%.
• The above condition is present for greater than 20 seconds.
Action Taken When the DTC Sets

• The fuel gauge defaults to empty.
• The low fuel indicator illuminates.
• The PCM records the operating conditions at the time the diagnostic fails. The PCM displays the failure information in the Failure Records on the scan tool.
Conditions for Clearing the DTC

• The DTC becomes history when the conditions for setting the DTC are no longer present.
• The history DTC clears after 40 malfunction free warm-up cycles.
• The PCM receives the clear code command from the scan tool.
Diagnostic Aids

Use the Freeze Frame and/or Failure Records data in order to locate an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data may aid in determining the number of miles since the DTC set. The Fail Counter and Pass Counter can also aid in determining the number of ignition cycles that the diagnostic reported a pass and/or fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature, etc.). This will isolate when the DTC failed.
Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Test Description

The number below refers to the step number on the diagnostic table.
Tests for the proper operation of the circuit in the low voltage range.
Step
Action
Value(s)
Yes
No
Schematic Reference: Instrument Cluster Schematics
1
Did you perform the Instrument Cluster Diagnostic System Check?
--
Go to Step 2
Go to Diagnostic System Check - Instrument Cluster
2
Install the scan tool.
Turn ON the ignition, with the engine OFF.
With the scan tool, observe one of the following fuel level parameters:
• Fuel Tank Level Remaining % parameter in the PCM Enhanced Evap Data list -gas only
• Fuel Level Sensor % parameter in the Engine Data Fuel System display-6.6L diesel only
Does the scan tool indicate that the Fuel Tank Level Remaining % or the Fuel Level Sensor % parameter is greater than the specified value?
98%
Go to Step 3
Go to Diagnostic Aids
3
Turn OFF the ignition.
Disconnect C152.
Connect a 3 amp fused jumper wire between the signal circuit of the fuel level sender and the low reference circuit of the fuel level sender (male terminal side).
Turn ON the ignition, with the engine OFF.
With the scan tool, observe the fuel level parameter.
Does the scan tool indicate that the Fuel Tank Level Remaining % or the Fuel Level Sensor % parameter is less than the specified value?
4%
Go to Step 6
Go to Step 4
4
Test the signal circuit of the fuel level sender for an open, a high resistance, or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 12
Go to Step 5
5
Test the low reference circuit of the fuel level sender for an open, a high resistance, or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 12
Go to Step 9
6
Test the signal circuit of the fuel level sender for an open, a high resistance, or a short to voltage between C152 and the fuel level sender. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 12
Go to Step 7
7
Test the low reference circuit of the fuel level sender for an open, a high resistance, or a short to voltage between C152 and the fuel level sender. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 12
Go to Step 8
8
Inspect for poor connections at the harness connector of the fuel level sender. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairsin Wiring Systems.
Did you find and correct the condition?
--
Go to Step 12
Go to Step 10
9
Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 12
Go to Step 11
10
Replace the fuel level sender. Refer to the following procedures:
• Fuel Level Sensor Replacement in Engine Controls - 4.3L
• Fuel Level Sensor Replacement in Engine Controls - 4.8L, 5.3L and 6.0L
• Fuel Level Sensor Replacement in Engine Controls - 6.6L
• Fuel Level Sensor Replacement in Engine Controls - 8.1L
Did you complete the replacement?
--
Go to Step 12
--
11
Important: Program the replacement PCM.
Replace the PCM. Refer to the following procedures:
• Powertrain Control Module Replacement in Engine Controls - 4.3L
• Powertrain Control Module Replacement in Engine Controls - 4.8L, 5.3L and 6.0L
• Engine Control Module Replacement in Engine Controls 6.6L
• Powertrain Control Module Replacement in Engine Controls - 8.1L
Did you complete the replacement?
--
Go to Step 12
--
12
Use the scan tool in order to clear the DTCs.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC reset?
--
Go to Step 2
System OK

P1093
Fuel rail pressure is low. This may or may not cause a MIL (check engine light). This is a very common problem that we hear about from our customers. Actual fuel rail pressure is not keeping up with Desired fuel rail pressure. This may only happen in high fuel demand situations like towing or racing or with everyday use.
Symptoms:
May include one or all and not limited to; Low power, poor shifting quality, excessive smoke, engine limp mode, reduced mpg.
Causes and repairs:
1. Dirty fuel filter is the most common issue we see. The filter should be changed in the 8,000-10,000 mile range if good fuel is being purchased and running mostly low HP tuning, much sooner if running competition/race style tuning. When in doubt, change the filter! This is about a 30 minute job that can be done without any special tools. Cost; Less than $50.00

2. Leaking fuel filter head, or cracked water separator. The filter head is the part that the fuel filter screws into and has the primer plunger incorporated into it. There are O-rings and seals that break down with age and use. ATPTrucks.com sells an inexpensive rebuild kit complete with instructions to repair this important part. The water separator screws into the bottom of the filter itself and must be replaced if cracked or damaged. Common hand tools are all that is needed. Approximate time is 1 hour. Cost: Less than $100.00

3. Weak fuel pressure relief valve (fprv) for 2004.5-2010 model years. This can be tested by doing the “bottle test” This is an easy, cheap way to see if the fprv is leaking. If any fuel is leaking past the fprv, then the internal spring will need to be shimmed. ATPTrucks.com sells the shim kit, including the proper parts needed to bring the spring pressure back to acceptable level to stop leaking relief valves. You will need an 18mm wrench and a bench vise. Approximate time is 1 hour. Cost: Less than $25.00.

4. Collapsing or cracked fuel line between the filter head and the high pressure fuel injection pump (cp3). This is usually caused from a plugged fuel filter causing a major vacuum between the filter head and the cp3. If not cracked, the problem is usually fixed by replacing the filter. The fuel line can be replaced if the filter change doesn’t fix the problem. Remove the fuel line and find a suitable replacement at the local auto parts store, making sure the line is rated for diesel fuel.

5. Blocked or broken fuel tank pickup. We have seen this many times. The common cause is a foreign object gets down the filler neck of the fuel tank. The most common thing we see is the paper seals of diesel fuel additive. This is not a fun job but is not too difficult. Run the fuel level down as much as possible, then the tank will have to be dropped. The fuel sending/pickup unit will then need to be pulled out. Inspect the unit as well as the fuel tank and remove the offending particles or repair the separated pickup tube. Tools needed: fuel line quick disconnect kit, can be the cheap plastic ones sold at the local parts store. Approximate time is 3-4 hours. Cost: is less than $20.00 unless the pickup/sending unit is damaged.

6. Weak CP3. We see this start to rear its ugly head at an average of 175,000 miles depending on the history of the vehicle. If the truck has had a lift pump (electronic pusher pump) and/or correct fuel filter changes, then this can be greatly extended. This CP3 is under high demand, sucking fuel from the tank through the filter and then converting this to pressures up to 26,000psi.

It is a mechanical pump and does wear with use. This is a big job to do as the CP3 is gear driven off of the camshaft and is located in the valley of the engine. I recommend having a qualified mechanic diagnosis this pump if the above repairs have not fixed the low rail pressure problem. The cost for parts alone will be $800.00-$1000.00 without installation. The mechanically inclined person can do this job, no specialty tools are needed but patience and time. The CP3 doesn’t need to be timed to the cam. Approximate time for the DIY’er would be 6-10 hours. Installing a lift pump may help fix the symptom and is a good modification for the future even if a new CP3 is needed. If a mechanic is out of the question, then installing a quality lift pump would be my first recommendation.

7. High injector return rates. This is also an expensive, time consuming job so I recommend having a qualified mechanic diagnosis the problem if you are at this point. Cost for parts and labor will vary depending on model and year. Parts costs can vary from $2000.00 to $4000.00 and labor from $600.00 to $1500.00.
To summarize, normal maintenance goes a long way in helping your truck survive in high demand situations. Most fuel pressure issues are not caused by tuning if the tuning was done correctly for the current modifications on the truck. Quality lift pumps will allow the engine to handle higher fuel demands and offer the benefit of cleaner fuel being supplied to the expensive fuel system. This holds true for stock or modified trucks. Hopefully this will help you with diagnosing your trucks fuel rail issues.

U1026 is a loss of communications with the transfercase control module.
P1026 Check ground 110 on the left frame under the driver's door area. Disconnect the transfer case control module and verify that it is getting power and ground, if so then replace the transfer case control module.


P1041 Verify a good ground at the black wire at pin A in the 2 cavity connector at the EBCM. Verify a good power on the red wire at pin B in the 2 cavity connector and a good power supply on the Brown wire at pin A1 in the 16 cavity connector. These are done with the key on. Establish scan tool link with the PCM. Using a jumper wire, short the Lt Blue wire at pin B6 in the 16 cavity connector. Within 3-10 seconds after ground, the scanner should go to "No Communications". If this does not occur then the this wire is broken. If this no communications does show then replace the EBCM.
 

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Discussion Starter #11
Thanks RVN4ME! That's the most feedback I've gotten since this all started. I printed your response and took to the dealer. I did learn that they unplugged the harness from transmission and suddenly we had at least third gear and reverse. They didn't even know that trick (came from Merchant). That has us thinking we are surely chasing an electrical gremlin.

The two fuel-related codes you reference that we have are pretty constant. Never caused an issue and I just attributed them to either the bed tank being also wired into the fuel gauge or the LBZ CP3 pump/regulator that Fleece installed. Never caused any issues though.

However the U1026 and U1041 didn't show up until the transmission stopped and after I cleared with my CTS, they haven't returned. And to answer your question, the harness was wet when I unplugged from the tranny (as Mike L told me to check in an earlier post regarding harsh downshifts), but cleaning both sides with a contact electrical cleaner and blowing with air nozzle didn't seem to help our current issue.

RVN4ME, is there a source of the electrical info you list for U1026 and U1041 that I might point my dealer to? Your information is very detailed and I pray, helpful (to the dealer). Thanks again so much for taking the time to respond!
Paul
 

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That info would be in the full-service manual, which the dealer should have already been referring to/using to figure out the problem with your truck.
 

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Discussion Starter #13
Does that manual show what voltages we should be seeing at each pin of the tranny end of the harness coming from tcm? If not does anybody know where that info can be found?
 

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I don't know what Allison info the FSM has, I've just gone through the 4l80e section of it about a year and a half ago when I rebuilt one to install in my truck.

Again, the dealer has this manual, and should already have been using it to figure out what's up, not throw parts at it...
 

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Discussion Starter #15 (Edited)
Well not sure where to turn now.
Tech can command solenoids with scanner and has manually moved them too.
No codes present other than shift range inhibited message. Tech says the ones in history or freeze frame or whatever it is would not be helpful.
Dealer unplugged harness and we have reverse and a forward gear.
They say that since ECM has tunes on it, We have to return it to stock via new $2,500 non-returnable ECM before we continue. And there's no real feeling whether that would help anything.
After being without truck for two months, I'd gladly pay that if we thought strongly that would get us back on the road. I'm not even sure buying another tranny would give different results.
I would reach out to Mike L but he will want codes and I have none.
I just am not sure where to turn at this point. The truck is WAY TOO NICE to part out.
Can you convert to a six speed manual transmission? I don't want to, but apparently I'm stuck at dealer as the only other Allison shops in the Nashville area just sell parts or service big equipment.

I should add that they are only working on it when their diesel guy has no other work to try to keep my bill down. It's been on one of his 2-3 racks for 4 weeks now.
 

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Dealer can't flash it back to stock? He should be able to do that...

You lose whatever tune is installed. Depending on your setup, you may be able to uninstall the tune before they reflash it.
 

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FWIW, $2500 for a ecm seem over the top, what about TCM? Lots of reading here so maybe I missed it. I would recommend Kennedy diesel for maybe a new ECM or TCM before paying dealer that kinda dough!
 

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Discussion Starter #18
Well I have managed to score a ECM for much less that can be returned. Hopes are that using that ECM with stock tunes will enable us to speak with GM engineering types. I still think it's a stuck e-valve or wire chafe but nobody is listening to me at this point.


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You should request your dealer try a known good tcm or from another truck .
 
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