Transmission Trouble ??

[Roy W]

I was pulling my travel trailer (10K loaded) up a moderate grade using tow haul a week ago when all of a sudden the transmission downshifted with a bang into 3rd gear and the check engine light came on. I continued up the grade in 3rd gear and pulled over at the top. Trans fluid was okay and was only 170 degrees when the downshift occurred. Finding nothing wrong I cycled the key a few times and pulled back out onto the highway. (With 1000 miles to go) The worry some part is the transmission had not downshifted back to low gear when I stopped and it started out from a dead stop in 3rd gear. Easing it along I drove a few miles (still locked in 3rd gear) keeping rpm around 2200 and transmission temperature under 200 degrees. After driving about 30 miles in this condition I found a large parking lot and pulled into it. Again fluid level was a little higher but not over the full mark. I again cycled the key about 5-6 times, but let the truck sit for about 20 minutes. This time when I pulled back out on the highway the transmission shifted normally and started out in 1st gear, but the check engine light was still on. After an overnight stop, the next day the check engine light was OFF and the transmission shifted normally for the rest of the trip home.......Trans sump fluid and filter were changed 5k before this occurred. 152K on transmission.......Any idea what happened. Shift solenoid ??

[DmaxMaverick]

The 3rd gear lock was limp mode. Something was amiss to cause that. Are you using any power-adder (Edge, etc.)? What you described is the same as when I get an overboost or tranny slip. You need to read the code to know what it was. It will remain in history for a while, even if the SES lamp isn't on. Most simple code readers will only show P0700 if it's a TCM code (which only means there is a DTC in the TCM, and it commands the MIL/SES). You'll need a more sophisticated scanner (Tech II, Snap-On) to read the TCM. Most modern shops will have one.

[Roy W]

I have an Edge EZ (kept in #1) that's been on the truck for 125K miles. I never thought to look at my ISO boost gauge when it happened and I do have a Kennedy Boost stick, although I have pulled many steeper grades than the one on which the fault occurred. I don't own an OBD II, but will buy one even if it's for a future occurrence.

[maverick_935]

long story but when mine did that i put it in to the tranny shop and the end result was the torque converrter had failed. apparently common on the 05's

[a5150nut]

Roy, Does your Edge read your engine/trans codes?

[Roy W]

No. it does not.

[Kennedy]

It is unfortunate, but these boxes with "slip protect" seem to have a tendency to degrade the transmission's holding capacity over time. I have also found that with the Boost Stick added the power increases significantly so I suggest that you back down the Edge at least one power level.

[Roy W]

My Edge EZ is already operating on #1 (the lowest level out of three).

[Kennedy]

Last one that I dealt with that had this combo and this issue we went to my 50HP tow tune direct in the ECM and he's been tickled pink ever since.

[More Power]

I'd want the code(s) before doing anything.

[Roy W]

I have an appointment with a Tech II Tuesday morning.

[Roy W]

The Tech II scan tool showed a TCM PO735 fault (Gear 5 incorrect ratio). The technician and I agreed that unless it does it consistently that we could be chasing goblins. I have pulled a 10K trailer 1000 miles since the fault occurred. Next trip is to Talladega, so we'll see what happens then.

[Kennedy]

P0735 is the slip in 5th gear that is common when the transmission's capacity is tested/overcome. It will very likely do it again and it will get worse the more that it happens. It's kind of a death by 1000 paper cuts deal.

[DmaxMaverick]

It slipped in OD. Edge + stick + (load conditions) allowed that to happen. Simple as that, and not a goblin. Either lock out OD or downgrade the power enhancers the next time you have a similar load on a similar grade. It's very likely that if you repeat the conditions, you'll repeat the result. Each slip gets more likely (the next time), at lesser loads.

[Kennedy]

Funny thing is, when working directly in the ECM we can make it more responsive, pull stronger, run cooler and still not limp the trans. There's something about the way the fueling comes on (delay then rush) and the fact that the ECM is not in direct control of it that tends to get under the Allison's skin.

[Roy W]

Locking out overdrive when pulling even a slight grade makes sense. Thinking back to the conditions when the fault first appeared, it was probably a 5% grade, but I had lugged 5th gear down to 55 mph (just before tow haul would have caused a downshift) while pulling the 10K lb travel trailer. I'm hoping the fault won't reappear when driving unloaded.........Thanks for all the assistance in working this thing out.

[EdHale]

The reason my 2006 is bone stock and staying that way. It tows plenty strong for me and gets 12.0 +/- 0.5 mpg towing my fifth wheel. When not towing at a steady 62 mph it gets 21.5 and has 155,000 on the odo.

I'm a happy camper and heading to Talladega next Wednesday.

[Roy W]

We'll be in site 807. Stop by,

[EdHale]

So you are in West Park B?

I will be in East Park, but I don't know the site # yet. I am a Shriner and will be doing some volunteering while there. We will be driving around on golf carts transporting fans that have problems walking distances. I should know my site # in couple of days.

When are you arriving? I will get there at noon'ish on 10-21, but will be on the night shift for the first couple of nights.

[Roy W]

I'm in Geico Green in the infield between turns 3 and 4. We'll be arriving 5pm Wednesday.