05 Sierra Transmission Codes

eand28

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Jun 7, 2015
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I bought a 05 Sierra with the 5 speed allison a year ago with 150k on it. Drove it back to Pennsylvania from Arizona and limped the transmission in Tennessee under heavy throttle trying to accelerate from 45 mph back to highway speed. Threw p0700 and p0735 gear 5 incorrect ratio. Truck was bone stock but it definitely spent a lot of time towing with the previous owner. Since then I’ve limped it 3-4 more times under the same conditions under the 5-4 downshift. The truck will go 1-5 under full throttle with no issues just the 5-4 shift.

I’ve towed 6k with the truck and it did fine going uphill holding 5th at 55-60mph.

Had some people saying it could be the transfer case but not sure exactly how to diagnose it. The truck will be getting a built trans in a few weeks. I’m thinking it might be a good idea to have the shop check the transfer case out while it’s out just to check.
 

eand28

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Jun 7, 2015
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Also want to add it'll run 1-5 with a 60hp tune with no issues. Still has the 5-4 issue under heavy throttle
 

JoshH

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It's pretty common to see those 5 speeds limp on a 5-4 down shift, but it usually isn't at stock power unless the truck had previously been tuned and limped several times before. I would guess that's what happened or it is still tuned and turned up a little too much for the stock trans. Your only real fix will be a rebuild on the trans.
 
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eand28

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The truck has only had one owner before me (older lady) and it lived in the Phoenix AZ area since new. There really aren't any indicators that the truck was previously tuned. I never drove a duramax before buying this but it drives how I thought a stock one would.

When I limped it the first time on the way home from AZ it was a quart or so low on fluid. Only issue with the t-case is a seeping output shaft seal

1645457575845.jpeg
 

eand28

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B09119D7-A895-465B-8AA9-947C9A3D85AB.jpeg

I believe Mike L. said something in another thread about 1400 rpm in 4th gear. Was that about the turbine speed or one of the speed sensors? The pic is of the truck in 4th gear at 40mph. Stock 245/75r16 tires
 

eand28

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I did beat on the truck a little bit on my way to work today and it shifted fine on the 5-4 downshift under heavy throttle around 50 mph multiple times in a row
 

eand28

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So limped it tonight on my way home from work. 55 mph up a slight incline and got the p0735 code again. Cleared it went and beat on it some more and it was fine. Honestly think it could be transfer case related. @Mike L. any input?
 

DuramaxNWA

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Feb 22, 2022
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So limped it tonight on my way home from work. 55 mph up a slight incline and got the p0735 code again. Cleared it went and beat on it some more and it was fine. Honestly think it could be transfer case related. @Mike L. any input?

When you checked the transmission fluid, did you follow the Allison procedure for that? PRND and back to P with the transmission fluid at or close to 180°?

You might want to take a second look at that transfer case and make sure it's really just a leak at the output shaft. That's exactly what mine looked like when it was really pump rub and about a week later I was ordering a new TC from Merchant Automotive.
 

eand28

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When you checked the transmission fluid, did you follow the Allison procedure for that? PRND and back to P with the transmission fluid at or close to 180°?

You might want to take a second look at that transfer case and make sure it's really just a leak at the output shaft. That's exactly what mine looked like when it was really pump rub and about a week later I was ordering a new TC from Merchant Automotive.
Yup I did the correct procedure for the fluid. I did crawl under the truck when I got it to check out the typical spots the pump rub comes through and it definitely is the shaft seal
 

DuramaxNWA

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Feb 22, 2022
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Yup I did the correct procedure for the fluid. I did crawl under the truck when I got it to check out the typical spots the pump rub comes through and it definitely is the shaft seal
Did you check the fluid level in the TC while you were under there? All good?

When you build the trans, it's a great opportunity to open that transfer case up and freshen it up a bit and make sure you have a pump rub kit in there.
 

Mike L.

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Did you check the fluid level in the TC while you were under there? All good?

When you build the trans, it's a great opportunity to open that transfer case up and freshen it up a bit and make sure you have a pump rub kit in there.
You need to look further at the forks to see if they are ok. Checking for pump rub has nothing to do with the rest of the TC.
 
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eand28

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I’m going to have the shop take a look at the tcase for slop when they have the trans out but I feel like if it was the shift forks it would case a problem more often than 4 times in the last 10k miles
 

eand28

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696DFF71-3945-417A-B3E5-03957440D66A.jpeg

This is pretty much the only spot on the transfer case that’s questionable. No obvious holes or cracks
 

dndj

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P0735 is a TCM code for "incorrect gear ratio". Some possible causes are slipping clutches, a bad input or output speed sensor, or bad/intermittent wiring to those sensors. The output speed sensor is on the tailshaft of the transfer case. Other causes that have been suggested are transfer case internals worn out enough for the sensor pickup ring to give false readings.

If it was my truck I would replace the input and output speed sensors first, and carefully check all the wiring for rub-through or bad spots from the sensors all the way forward to the TCM. After that, start with the hard parts. If i was pulling the trans for a rebuild anyway, I would definitely go through and check the transfer case internals at the same time.
 

eand28

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Trans is getting rebuilt this week and I’m having them look at the transfer case as well
 

eand28

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8DE3EE01-0083-439B-909E-CAFA68487E38.jpeg


Got the trans built and noticed the other day a leak coming from the inspection cover. Seems like it likely is the front pump seal from what I’ve read. Converter is new so I don’t think it’s the cause
 

PureHybrid

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I'd wash the bellhousing out the best you can, and see if it keeps leaking. If the shop tried to prefill the converter, it'll make a mess when they install it. And it's a pain to clean out.

Worst case it's the orings leaking on the pump bolts or the front seal itself. I might be a hack, but I only change the front seal if it looks to be leaking during a rebuild
 
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eand28

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I'd wash the bellhousing out the best you can, and see if it keeps leaking. If the shop tried to prefill the converter, it'll make a mess when they install it. And it's a pain to clean out.

Worst case it's the orings leaking on the pump bolts or the front seal itself. I might be a hack, but I only change the front seal if it looks to be leaking during a rebuild
Just pull the inspection cover and hose it out? I honestly didn’t look under it when I picked it up and only noticed it the other day putting my amp steps on
 

eand28

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@Mike L. Is the EFI fast relearn still inferior to reseting everything via Tech 2? I've put about 2k miles on my freshly built trans and under 30% throttle shifts feel very delayed/slow. I was thinking of relearning the transmission again but I'm leaning towards having the dealer reset everything with tech 2 vs me just doing a fast learn with my autocal or foxwell scanner