Author Topic: Duramax transmission/other problems (Read 2009 times)

Flyin6 · « **on:** July 29, 2019, 03:07:28 PM »

So, I was driving my truck into town a little while ago and I thought that the engine was revving a bit higher than usual, showing 2100 RPM when 1900 would be more like normal

Sort of like the converter was unlocked

Then when I pull off the highway, into town and take off from the first traffic light, the truck acts like the converter or clutches are slipping. It revs and sort of gradually picks up speed. Nothing like before. It did that several more times before I stopped to pick up something.

Coming back out, I started the truck and placed it in Reverse. It didn't do anything. And oddly, the little line that appears beneath the gear you have selected was missing. Then I got some message telling me I needed to shift into neutral to reset shifter...???

I did that a couple times and then it shifted into a sloppy reverse. Revving to get moving and all that.

Then the engine started a high idle of about 900 RPM and would "Tumble" or skip every once in awhile

I shut it down and started it back up a couple times and that condition abated.

I had to drive 15 miles back to home on the highway and I could only maintain 60MPH and the transmission would not upshift past whatever gear it stayed in (4th??) at 60MPH I was pulling 2500-2600 RPM.

Watching the transmission temp, it started out at a cool 170 and along the drive home rose to reach 203. It does not normally get that high, more routinely 187-194

So what's up?

Neutral solenoid acting up? Wiring harness?? Tune? Trans going out??

Yesterday I pulled a 4,000 lb trailer and a 1,500 lb mower home at 55mph, but that went well, and showed nothing abnormal at all.

Flyin6 · « **Reply #1 on:** July 29, 2019, 04:02:05 PM »

Just found this:
Moisture inside park/neutral/backup switch

#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 DuramaxTM 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.

JR · « **Reply #2 on:** July 29, 2019, 04:46:38 PM »

You have the later Allison with the switch inside the pan.

KensAuto · « **Reply #3 on:** July 29, 2019, 05:24:53 PM »

Yeah^^
Sounds like it's limping.

EL TATE · « **Reply #4 on:** July 29, 2019, 06:45:42 PM »

x2. sounds like the converter is going out and the trans is going into limp to preserve it.

TexasRedNeck · « **Reply #5 on:** July 29, 2019, 09:21:53 PM »

I had problems with mine and it was the C solenoid.

Scan it with a good tool.

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Bigdave_185 · « **Reply #6 on:** July 29, 2019, 10:15:21 PM »

I had similar issues and the problem was in the shifter handle it self. MikeL replaces the shift handle and the old wires were cracked and broken and barely connected

I would start there myself. Simple to check

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JR · « **Reply #7 on:** July 29, 2019, 10:17:44 PM »

Any codes??

JR · « **Reply #8 on:** July 29, 2019, 11:53:00 PM »

Your DD right now, right?

Order a built trans, get it installed and call it done.

Flyin6 · « **Reply #9 on:** July 30, 2019, 09:48:05 AM »

Well, last night I had to go to a fire dept board meeting and drove. It shifted into neutral between shifts resulting in a flare shift, but then in a few minutes acted perfectly normally again. When I drove it home it was completely normal with the PRNDM-! underscore illuminated.

I am thinking the trans is fine, but with some electrical/electronic malfunction. going to get it scanned...standby

TexasRedNeck · « **Reply #10 on:** July 30, 2019, 10:45:37 AM »

I had a TCM go bad on my LML. Ironically not too long after the PPEI trans tune. Never reloaded it after the new TCM was installed.

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JR · « **Reply #11 on:** July 30, 2019, 10:59:04 AM »

Hope it is simple. Sounds more electrical than mech.

Flyin6 · « **Reply #12 on:** July 30, 2019, 12:27:20 PM »

Results from the scan:

First pull there was three pages of codes, many repeats, almost all transmission related, and most relating to high temp.

So many, if fact, that we decided to just clear everything out and try it again after a test drive. During the drive it flare shifted, ran normally, gave me one very hard upshift, then started slipping and went into 3rd gear limp mode on the way back

Pulling the codes this time pointed to the temp sensor which is bundled in the TCM that is inside of the pan. I noted that while it was reporting high temps it was also reporting high voltage and low voltage from the same sensor.

The trans temp gage showed 174 degrees while it was throwing the high temp codes while driving very lightly loaded at 45 mph and not slipping.

We have a call out to GM and others pricing that TCM which is dealer priced at $689!!!! Ouch. Couple to that ten or so quarts of trans fluid, a spin on filter, internal filter, and a gasket along with a flash of the TCM ($130) and I have about a grand going out the door pdq.

On the positive side while I was in there I noted Troy talking to a guy with a tractor about moving some dirt around his pond. I suggested a trade of labor...??? Maybe???...

JR · « **Reply #13 on:** July 30, 2019, 12:35:55 PM »

TCM is in the engine compartment. Solenoids, temp and PDN switch is in the pan.

JR · « **Reply #14 on:** July 30, 2019, 12:40:42 PM »

Your module is under $240 on amazon

Flyin6 · « **Reply #15 on:** July 30, 2019, 05:18:21 PM »

Quote from: JR on July 30, 2019, 12:40:42 PM

Your module is under $240 on amazon

Thanks JR

I know the TCM is on the radiator shroud, but looking at the scan tool, it was calling the module inside the pan a TCM as well. It confused me too. I thought we were talking about the big thing, not the consolidated sensor thing inside the pan.

I'll check out the amazon. Troy found one for just a couple hundred as well.

But here's what has happened. I was checking around the thing and when I checked the trans fluid to see if it smelled burned, I noticed it was 2 quarts low! And no foul smell at all, in fact it looked great!

So I guess I never saw any fluid leaks, no wet spots at all, so never suspected a low fluid condition. I added two quarts of valvoline Dex VI and drove it.

and know what?

It is completely normal. Like not one hiccup at all. Afterward I spoke with Troy who liked the result, however still questioned why we had both a high and a low voltage reading on the temp output. I think I have an idea

It is either that module inside the trans is failing (Intermittent) or maybe I have an electrical connection acting up. I know the 5-speed Allisons were famous for those pins coming loose and causing all manner of headaches. So at a minimum I'm going to pull and check and coat with dielectric grease. If I see nothing thereafter for say a week, then I'll consider the problem resolved. If it acts up, I'll change out that module and go from there

In any event, time for a fluid/filter change.

TexasRedNeck · « **Reply #16 on:** July 30, 2019, 05:51:43 PM »

Oh no!!! Not a fluid change!!

Lol

Don the piece in the pan is a manifold pressure switch.

I may have one that fits it. I replaced mine on the LB7 before we found the solenoid was bad. Trans problems throw all kinds of weird codes that can make you chase a ghost.

I’ll have to check the part number to see if the LML and LB7 take the same one but if it is I can send it to you so you can swap it out if it comes down to playing whack-a-mole parts replacement.

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JR · « **Reply #17 on:** July 30, 2019, 08:26:39 PM »

Quote from: Flyin6 on July 30, 2019, 05:18:21 PM

I noticed it was 2 quarts low! It is completely normal. In any event, time for a fluid/filter change.

Shows you how sensitive these things are. Just glad its OK.

KensAuto · « **Reply #18 on:** July 30, 2019, 08:53:23 PM »

No module in the pan. That's on the gassers...6 speeds. The Ally has conventional switch's and solenoids like JR mentioned.
.. high and low voltage sensor codes, together, usually points to a bad connection somewhere. I would guess at the TCM.

You have the codes, for giggles?

JR · « **Reply #19 on:** July 30, 2019, 09:01:17 PM »

I think that's why they moved the PND module to the pan. No exposed plugs or condensation issues in the pan. Pain to change, but a more stable environment for mulch crushers,,,,,,

Think I'll check my tranny fluid since I need to change fuel filters.

rpar86 · « **Reply #20 on:** August 01, 2019, 07:33:45 PM »

Quote from: Flyin6 on July 30, 2019, 05:18:21 PM

Quote from: JR on July 30, 2019, 12:40:42 PM
Your module is under $240 on amazon

Thanks JR

I know the TCM is on the radiator shroud, but looking at the scan tool, it was calling the module inside the pan a TCM as well. It confused me too. I thought we were talking about the big thing, not the consolidated sensor thing inside the pan.

I'll check out the amazon. Troy found one for just a couple hundred as well.

But here's what has happened. I was checking around the thing and when I checked the trans fluid to see if it smelled burned, I noticed it was 2 quarts low! And no foul smell at all, in fact it looked great!

So I guess I never saw any fluid leaks, no wet spots at all, so never suspected a low fluid condition. I added two quarts of valvoline Dex VI and drove it.

and know what?

It is completely normal. Like not one hiccup at all. Afterward I spoke with Troy who liked the result, however still questioned why we had both a high and a low voltage reading on the temp output. I think I have an idea

It is either that module inside the trans is failing (Intermittent) or maybe I have an electrical connection acting up. I know the 5-speed Allisons were famous for those pins coming loose and causing all manner of headaches. So at a minimum I'm going to pull and check and coat with dielectric grease. If I see nothing thereafter for say a week, then I'll consider the problem resolved. If it acts up, I'll change out that module and go from there

In any event, time for a fluid/filter change.

Where do you plan on putting the dielectric grease - on connections in the pan? Might want to make sure its compatible with being in a bath of trans fluid. Low fluid definitely can make these Allys act weird, so I bet that was your main issue.

Flyin6 · « **Reply #21 on:** August 01, 2019, 08:37:45 PM »

The D-Grease is intended for external connections.

Some of the parts came in, just waiting on the fluid and the filters, so anticipating a delivery tomorrow, in the morning I'll pull the pan off and get ready to finish it all up.