Transmission hiccup

[Tin Lizzy]

Hi all. I would appreciate some input regarding the use of manual (command shift) transmission control in light of a recent hiccup when towing a 2.5T caravan down Dorrigo Mountain NSW in my MY15 D4 - 8 Spd transmission. I am new to the caravan game also 😳. Because I get frustrated the way command shift keeps switching back to auto mode when no gear changes are made, I selected Sports mode command shift and headed down the mountain, holding most of the way in 2nd or 3rd gear (Redarc tow pro in use also). At the bottom of the mountain I pulled over and re-selected D Auto....this caused the transmission to become nearly unresponsive.....virtually no throttle response at all. Stopped and let things cool down for 15mins, and was relieved that normal operation then seemed to be restored. My question - is it ok to use Sports command mode to hold gear for engine braking when lugging my van down (or uphill)....or what else may have caused the loss of power in this situation. (ps transmission serviced at 40K......due again now at 80K). Any thoughts on this issue? Thanks.

[Barraman]

I also have a 2015 TDV6 with 8 speed auto - and I tow a 2.5 T boat/trailer with electric/hydraulic brakes 10,000+ km/yr. I tow in "S" generally and always use the cruise control where appropriate. I tow up and down the Toowoomba range and Cunningham's Gap roads annually (Dorrigo - like). When going down a steep road I use the paddles to lock in an appropriate gear to hold a safe speed without over use of brakes. I generally let the cruise control handle the up hill - or use the paddles if the CC is not doing keeping the revs up as well as I would like.

My gearbox has 180,000 km on it with services at 80 and 160 and is as smooth as silk. I have not seen the issue you describe.

On my current trip I have been using my Gap tool to monitor engine coolant and transmission oil temps while towing. Cruising on gently undulating roads at 100 kph and outside temp of 30oC, coolant temp is around 98oC with transmission temp about 5 degrees less. Interestingly, for me at least, pulling up a steep range at 80 down to 50 kph in 8th down to 4th gear, both temps stabilize at 104oC.

[Graeme]

Stopped and let things cool down for 15mins

Are you sure that anything had overheated? Maybe the engine and/or the transmission got too cold on the over-run without any combustion to keep the engine warm.

[josh.huber]

I tow a bit. Nothing drastic. Hills up and down. Little regard for the car when I do and often shift in and out of sports or command on the fly. Normally because I want cruise control to do is job without me.. I guess I'm lazy. If the throttle was unresponsive for a reason you should have received a heap of lights on the dash.
Pull into a dealer or Indy and check for codes for peace of mind.
But with the engine braking down hill. Revs would be up. Which means circulation is good. Torque converter locked. So no heat there. Maybe something much simpler. But that's the way I think all of us drive.
First time with a caravan chasing you is nothing you ever forget. Hopefully it's nothing

[Tin Lizzy]

I also have a 2015 TDV6 with 8 speed auto - and I tow a 2.5 T boat/trailer with electric/hydraulic brakes 10,000+ km/yr. I tow in "S" generally and always use the cruise control where appropriate. I tow up and down the Toowoomba range and Cunningham's Gap roads annually (Dorrigo - like). When going down a steep road I use the paddles to lock in an appropriate gear to hold a safe speed without over use of brakes. I generally let the cruise control handle the up hill - or use the paddles if the CC is not doing keeping the revs up as well as I would like.

My gearbox has 180,000 km on it with services at 80 and 160 and is as smooth as silk. I have not seen the issue you describe.

On my current trip I have been using my Gap tool to monitor engine coolant and transmission oil temps while towing. Cruising on gently undulating roads at 100 kph and outside temp of 30oC, coolant temp is around 98oC with transmission temp about 5 degrees less. Interestingly, for me at least, pulling up a steep range at 80 down to 50 kph in 8th down to 4th gear, both temps stabilize at 104oC.

Thanks for the input..... At least I am now happy that Sports mode is ok for engine braking...hadnt considered using cruise control to assist. Don't have a diagnostic tool yet, but strangely no fault/warnings were shown on the dash. Will have a checkup with my Indy if I can get back across the Qld border!

[Tin Lizzy]

Are you sure that anything had overheated? Maybe the engine and/or the transmission got too cold on the over-run without any combustion to keep the engine warm.

I don't have the smarts to think about that, but will run it past my mechanic when I take it in next. Thanks.

[Tin Lizzy]

I tow a bit. Nothing drastic. Hills up and down. Little regard for the car when I do and often shift in and out of sports or command on the fly. Normally because I want cruise control to do is job without me.. I guess I'm lazy. If the throttle was unresponsive for a reason you should have received a heap of lights on the dash.
Pull into a dealer or Indy and check for codes for peace of mind.
But with the engine braking down hill. Revs would be up. Which means circulation is good. Torque converter locked. So no heat there. Maybe something much simpler. But that's the way I think all of us drive.
First time with a caravan chasing you is nothing you ever forget. Hopefully it's nothing

I thought the same thing about no warnings also?? Luckily I was still on a slight downhill run, so could coast into a pull-off spot. Still getting used to the giant dog kennel hanging off the back of my Disco, but my knuckles are less white lately 🥴

[Tin Lizzy]

I also have a 2015 TDV6 with 8 speed auto - and I tow a 2.5 T boat/trailer with electric/hydraulic brakes 10,000+ km/yr. I tow in "S" generally and always use the cruise control where appropriate. I tow up and down the Toowoomba range and Cunningham's Gap roads annually (Dorrigo - like). When going down a steep road I use the paddles to lock in an appropriate gear to hold a safe speed without over use of brakes. I generally let the cruise control handle the up hill - or use the paddles if the CC is not doing keeping the revs up as well as I would like.

My gearbox has 180,000 km on it with services at 80 and 160 and is as smooth as silk. I have not seen the issue you describe.

On my current trip I have been using my Gap tool to monitor engine coolant and transmission oil temps while towing. Cruising on gently undulating roads at 100 kph and outside temp of 30oC, coolant temp is around 98oC with transmission temp about 5 degrees less. Interestingly, for me at least, pulling up a steep range at 80 down to 50 kph in 8th down to 4th gear, both temps stabilize at 104oC.

Sorry..thought I had replied to your info, but it seems to have disappeared.... Thanks for confirming that it is ok to use Sports mode for heavy load engine braking. Although there were no dash warnings received I will be getting myself an OBD tool asap after this little episode. All seems ok now though. Thanks for the response.

[Eric SDV6SE]

The ZF trans are pretty strong, so no issues there,not sure why youd be using sport and second gear, let the cars brain do the work. Cruise control and properly set up caravan brakes and HDC in really steep bits should sort it. Remember the mechatronic is adaptive.

[Milton477]

The ZF trans are pretty strong, so no issues there,not sure why youd be using sport and second gear, let the cars brain do the work. Cruise control and properly set up caravan brakes and HDC in really steep bits should sort it. Remember the mechatronic is adaptive.

I tow - a lot. In Sport mode the gear selected by the paddles is maintained indefinitely as long as you are in the correct speed range etc. In Drive, a gear selected by the paddles is held for a few seconds & then reverts to automatic changing. So, going down a hill you would want to maintain a gear, not have the mechatronic decide that it can change up because the brakes are good enough to slow the rig.
I wouldn't select HDC in this circumstance unless you want your nose to meet the windscreen in a hurry