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Arrow Allison Transmission - no go

Truck in question - 04 Chevy Crew cab 2500HD with the 6.6TD and allison transmission.

The intermittant problem that is occuring is that when the truck is started and shifted into gear, The check engine light comes on and the truck will not engauge into any gear.

Codes that are found are - P0700 - Trans Ctrl Sys Error
- P0846 - Trans Fluid pres sensor/switch
range/perf.
Codes found using th BD Power intimidator.

Truck seems to try to engauge as you increase throttle. (But its a sudden, jerky engaugment.)

Truck was returned to stock using the programmer, and still no change in behavior.

Any help is much appreciated.
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P0846 is indicating that the pressure switch D has not turned on when solenoid D is commanded. P0700 is just an indication that the Transmission Control Module (TCM) has requested the MIL (check engine light). The Allison uses a Presssure Switch Manifold (PSM) on the valve body which is a series of electrical pressure switches to indicate to the TCM that a particular hydraulic circuit is functional based on whichever solenoid is commanded. When there is a fault with the PSM, the TCM will either not allow any further shifts (if it is already engaged into gear) or will not allow any gear enagement at all (say, if your shifting out of park into any drive position).

The two likely causes for this problem is either a failed PSM (which is very possible), or the shift valve D is sticking in the valve body.
__________________
1993 GMC K2500 6.5 T.D. VIN 'F', 4L80E, 4:10
AFE cold air intake, 3" exhaust w/ downpipe, 241k miles and still running strong.
ASE Certified Master Automobile Technician w/ Advanced Levels Auto Engine Performance & Electronic Diesel Diagnosis
Now currently out of the auto repair trade and into ammunition manufacturing !
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Would replacing the valve body with an aftermarket valve body replace said parts? Or would that not include the PSM?

This problem has happened before - mostly after setting for a few weeks. Eventually after clearing the codes the problem went away. Today I just moved the truck onto the street, and it went about 20 feet and then just went into neutral, disengauging the transmission. Trued several times to clear the computer and reset it, but nothing changed.

Is there anything that causes these to go bad or stick? Or is it just a common thing for these trucks?
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I'm not positive, but I do believe that BD's valve body comes with the PSM. The PSM is kind of like a printed circuit with these electric pressure switches that are activated by certain hydraulic circuits. I wouldn't say that it is really common, but over time, heat can cause the PSM to crack resulting in failure of the pressure switch circuits. The PSM is a major input for the TCM and this is why BD includes a new one with their valve body (like I said, I believe they do).

A sticking shift valve is not as likely to be the cause, but it is still possible. This would usually be caused by a piece of debris lodged in the hydraulic circuit. I should mention also that a failing solenoid D would cause this as well since if the solenoid were to malfunction, the shift valve would not stroke and the pressure switch would not activate. I do NOT believe that BD's valve body comes with any of the solenoids; you need to re-use your originals.
__________________
1993 GMC K2500 6.5 T.D. VIN 'F', 4L80E, 4:10
AFE cold air intake, 3" exhaust w/ downpipe, 241k miles and still running strong.
ASE Certified Master Automobile Technician w/ Advanced Levels Auto Engine Performance & Electronic Diesel Diagnosis
Now currently out of the auto repair trade and into ammunition manufacturing !
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I don't know if you allready fixed your problem but....

I had that same problem and the same codes and after doing some troubleshooting it ended up being the ignition switch. The switch was loosing contact and not giving ingnition power to the TCM which in turn was not powering the pressure switches.
__________________
2002 GMC Duramax 2500HD
Edge Juice, BD X-Monitor,K&N Intake
5 inch Exhaust,Air Bags in Rear,8 inch custom Lift,Front Straight Axle Conversion
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Quote:
Originally Posted by Zetroc01 View Post
I don't know if you allready fixed your problem but....

I had that same problem and the same codes and after doing some troubleshooting it ended up being the ignition switch. The switch was loosing contact and not giving ingnition power to the TCM which in turn was not powering the pressure switches.
This is a good point!! Thank you for mentioning this.

From about 1996 and on, GM's ignition switches have been troublesome. The most common circuit to fail on the ignition switch is the one that provides power to the automatic transmission and instrument cluster. If you happen to notice that something is not working on the instrument cluster at the same time the tranny won't go into gear, this a good sign of a failed ignition switch. This applies to a number of GM body styles.
__________________
1993 GMC K2500 6.5 T.D. VIN 'F', 4L80E, 4:10
AFE cold air intake, 3" exhaust w/ downpipe, 241k miles and still running strong.
ASE Certified Master Automobile Technician w/ Advanced Levels Auto Engine Performance & Electronic Diesel Diagnosis
Now currently out of the auto repair trade and into ammunition manufacturing !

Last edited by DieselDude : 07-18-2008 at 04:09.
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Too many keys on the key ring...
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allison

I also had a code 700 tans sys control,I phoned bd ans they said to clear it,I foregt the part that is a comon problem related to thois code hope this helps..clayton.m@telus.net
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Quote:
Originally Posted by Zetroc01 View Post
I don't know if you allready fixed your problem but....

I had that same problem and the same codes and after doing some troubleshooting it ended up being the ignition switch. The switch was loosing contact and not giving ingnition power to the TCM which in turn was not powering the pressure switches.


Well I installed a BD diesel valve body on the truck in an effort to solve the problem. After I got the truck all backtogether and running, it ran great. (this was roughly a day after my first post was made)

Did some driving and some towing with no problems whatsoever. The truck ran great!

Went to start it up today, after exactly 1 week of setting, and it is back to exactly the same things it was doing before. Same codes also. How hard is the ignition switch to replace?
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The ignition switch isn't difficult to replace, although it is a little tricky. You don't need to remove the steering wheel or air bag, just the steering column covers. The ignition switch is held in by a couple of tiny inverted torx screws that takes a special socket to R&I.

After looking at the wiring diagrams for your truck, I'm having second thoughts about the ignition switch being the cause. The reason is that the TCM provides all the power inputs to the transmission, not the ignition switch. While the ignition switch does provide ignition power to the TCM, the same circuits also provide ignition power to the ECM and body control module. If the ignition switch were the cause with this circuit, I would think you would be experiencing some other problems as well.

You can verify that the ignition switch is the cause by performing a voltage drop test on the ignition switch circuits. While you are experiencing your problem (don't shut off the truck), using a DVOM, connect the positive lead to the postive terminal of the battery, then start probing ALL of your fuses with the negative lead. You should not see more than .100V drop on any of these circuits. More than about a .2V drop is readon for suspicion, and more than a 1V drop certaintly indicates a problem. The specific fuses that you should pay attention to for your transmission problems are in the fuse box in the cab and are labeled "IGN 0" & "TBC IGN 0". Both are 10A fuses. Make sure you check all the others, both in the cab and under the hood. Let me know which fuses have excessive voltage drops and I can see if they are on related circuits.
__________________
1993 GMC K2500 6.5 T.D. VIN 'F', 4L80E, 4:10
AFE cold air intake, 3" exhaust w/ downpipe, 241k miles and still running strong.
ASE Certified Master Automobile Technician w/ Advanced Levels Auto Engine Performance & Electronic Diesel Diagnosis
Now currently out of the auto repair trade and into ammunition manufacturing !
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Thanks for your information DieselDude. I checked the aformentioned fuses, as well as all fuses in the dash panel, and under the hood. They all tested good.

I did not however, have time to check

I did install a new backup/neutral saftey switch today, with really no effect. The only thing we did gain, is that the gear indicator is not dissapearing as the "shift range inhibitor" message came across the display. The new one was from a local parts store. I'm still going to replace it from a new one from Allison.

Had a mechanic friend of mine stop by today with his professional scan tool. With the old backup/neutral saftey switch, when switching between gears, the display would say "invalid". (along with the gear indicator light not appearing.) After installing the new one and noticed that their is slight adjustment by rotating the switch, we dialed it (the new one, and then the old one again) so where there were no invalid gear display. That fixed at least the gear indicator problem.

I did however pull some more codes

P0846 - Trans Fluid Pres Sensor/Switch b Circ Range/perf
P0841 - Trans Fluid Pres Sensor/Switch A Circ Range/perf
P0843 - Trans Fluid Pres Sensor/Swith A Circ Hi

Solenoids? Im thinking about just ordering a new set, and replace them all at once.
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Also to summarize.

- Gear indicator is illuminated on correct gears on the dash.
- range shift inhibited displays.

Since my gear selection is illuminated correctly, does this mean the nsbu is aligned correctly?



Ps. Are their any more indepth service/repair manuals for the newer gm trucks?
I deal with vw's alot, and I use a Bently service manual, which is much more helpful than any chiltons/haynes manual.
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P0841 & P0843 have to do with the Transmission Fluid Pressure (TFP) Switch 'C'. P0846 has to do with TFP Switch 'D'. Both of these are part of the Pressure Switch Manifold. Did your valve body come with the PSM? A bad electrical connection or a bad PSM are the likely causes for these codes. Faulty solenoids &/or stuck shift valves can also cause these codes, but faults with multiple shift valves or solenoids are not as likely as a poor connection or fault with the PSM.

You're on the right track about your shift indicator malfunction being caused by the gear selector positoin switch, but this part will not cause these codes.
__________________
1993 GMC K2500 6.5 T.D. VIN 'F', 4L80E, 4:10
AFE cold air intake, 3" exhaust w/ downpipe, 241k miles and still running strong.
ASE Certified Master Automobile Technician w/ Advanced Levels Auto Engine Performance & Electronic Diesel Diagnosis
Now currently out of the auto repair trade and into ammunition manufacturing !

Last edited by DieselDude : 09-02-2008 at 03:37.
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Update -

New nsbu switch from allison installed, with no improvements. (atleast its new)

Ordered C, D , and E shift solenoids from the local allision shop.

What exactly does the psm include? When I installed the new valve body, I'm pretty sure all that I swapped were the solenoids from one valve body to the other. It's been a while since I changed that, so im going off of memory.

Also another note. Checked the fluid level when the truck was cold. It appeared to be showing at the "hot" level indicator. Im positive it was correct when the valve body was installed. I checked it several times.
(Changed the external filter and got the fluid level back down where it was suppose to be.)

Drainback problems?
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The PSM includes the trans fluid temp sensor and the hydraulic pressure switches 'C', 'D', 'E', & 'Rev'.

I think there is a confusion with terminology because I am showing trim solenoids 'A' & 'B'; shift solenoids 'A', 'B', & 'C'; TCC solenoid; and solenoid 'G' which is the main line pressure solenoid.

Make sure you are checking the fluid level with the engine idling, and with the transmission at normal operating temp. Checking the fluid level when cold is OK, but it is more accurate if the fluid is warm. I don't think there is a drain back issue. Even if there is, as soon as you started the engine, the fluid would be pumped right back into the torque converter. The only issue that you would experience with a drain back issue is a delay engaging into gear when cold only.

The problem you're experiencing probably isn't all that complicated to diagnose and repair, although it can be difficult to give accurate advice over this forum. I'm just going off what you tell me and if I (or any other shop) had the chance to check it out personally, I'm sure the problem would be isolated relatively quickly.
__________________
1993 GMC K2500 6.5 T.D. VIN 'F', 4L80E, 4:10
AFE cold air intake, 3" exhaust w/ downpipe, 241k miles and still running strong.
ASE Certified Master Automobile Technician w/ Advanced Levels Auto Engine Performance & Electronic Diesel Diagnosis
Now currently out of the auto repair trade and into ammunition manufacturing !

Last edited by DieselDude : 09-05-2008 at 05:44.
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Thanks for all your help. I now understand what exactly the PCM is and the Trim solenoids A and B, and I know C is right above them. However im having trouble figuring out the rest. I would assume the next two are D & E, and F (the oddball) and G on the far upper right of this picture.

Do I have this correct?

http://www.transmissioncenter.net/Allison16.jpg


Putting the new solenoids in today.
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Quote:
Originally Posted by Jetta9621 View Post
Thanks for all your help. I now understand what exactly the PSM is and the Trim solenoids A and B, and I know C is right above them. However im having trouble figuring out the rest. I would assume the next two are D & E, and F (the oddball) and G on the far upper right of this picture.

Do I have this correct?

http://www.transmissioncenter.net/Allison16.jpg
This is correct. Solenoid 'F' is for the TCC and 'G' is the main line pressure solenoid.
__________________
1993 GMC K2500 6.5 T.D. VIN 'F', 4L80E, 4:10
AFE cold air intake, 3" exhaust w/ downpipe, 241k miles and still running strong.
ASE Certified Master Automobile Technician w/ Advanced Levels Auto Engine Performance & Electronic Diesel Diagnosis
Now currently out of the auto repair trade and into ammunition manufacturing !
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