P0740 Code Only While Towing
Rookie
Joined: Jul 2014
Posts: 87
Likes: 0
From: Midwest
I tow a single axle 3500 lb max camping trailer that has a lot of wind resistance. With the 3.21 gears, I always use tow/haul and mostly lock out the 2 overdrives. At 1:1, the torque converter locks up readily and at 65 MPH the RPMs are at 2,200. Sometimes I allow the first overdrive depending if the wind is calm or I have a tailwind. Last trip of about 600 miles RT, I got a hand calculated 11 MPG. What I like about getting the TQ to lock up, is that the trans temps are a lot cooler.
Here is the full operation and the differences of ERS and Tow/Haul modes explained for the 09-11 Ram 545RFE transmission.
Lets start off with the gear ratios of the 545RFE. There are 6 possible gear ratios but the truck will only let you use 5 of them at a given time.
1st 3.00:1
2nd 1.67:1
2nd Prime 1.50:1
3rd 1.00:1
4th 0.75:1
5th 0.67:1
In normal Drive mode when up shifting you will use gears 1, 2, 3, 4, & 5. In ERS or Tow/Haul mode you will use gears 1, 2, 2P, 3, & 4.
So, when in normal Drive mode:
1=1st 3.00:1
2=2nd 1.67:1
3=3rd 1.00:1
4=4th 0.75:1
5=5th 0.67:1
When in ERS or Tow/Haul mode:
1=1st 3.00:1
2=2nd 1.67:1
3=2nd Prime 1.50:1
4=3rd 1.00:1
5=4th 0.75:1
As you can see, ERS and Tow/Haul lock out 5th gear (0.67 ratio) but adds use of 2nd prime in the up shift pattern. ERS and Tow/Haul are the same as far as shifting order and gear limiting goes, Tow/Haul just holds each gear longer and downshifts much sooner when slowing down for engine braking. ERS and Tow/Haul mode also disables the use of MDS.
End of find.
I also will be towing a travel trailer @ 5,000 lbs. My thinking is that I will just use ERS and lock out 5=4th - 0.75:1 as you mentioned (if needed).
I'm trying to research before heading out in order to avoid throwing codes or overheating the trans Lol.
Thanks
Rookie
Joined: Jul 2014
Posts: 87
Likes: 0
From: Midwest
After action report
First time towing with the RAM 1500 was a positive experience.
My truck has the 3:55 gears.
60 mph towing a TT = 5th gear was not happening.
Start of trip- placed selector in Drive. Pushed Tow/Haul button. Evic automatically displayed ERS 5.
Truck was rock solid at 60 mph. Trans was running in 4th gear, converter locked, 2,200 rpm. Shifted to 5th and rpm's dropped down to 1,500. Engine bogged down and started losing speed. Spead up to 65 and tried again...no go.
Left trans in 4th gear, set cruise, and let it roll. Small incline caused unlocked converter condition. Had to use the skinny pedal to keep it locked on hills.
Trans temp was a steady 141 degrees F. Outside air was 80 F.
My truck has the 3:55 gears.
60 mph towing a TT = 5th gear was not happening.
Start of trip- placed selector in Drive. Pushed Tow/Haul button. Evic automatically displayed ERS 5.
Truck was rock solid at 60 mph. Trans was running in 4th gear, converter locked, 2,200 rpm. Shifted to 5th and rpm's dropped down to 1,500. Engine bogged down and started losing speed. Spead up to 65 and tried again...no go.
Left trans in 4th gear, set cruise, and let it roll. Small incline caused unlocked converter condition. Had to use the skinny pedal to keep it locked on hills.
Trans temp was a steady 141 degrees F. Outside air was 80 F.