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 15minsAre 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[bigwhistle]

[Eric SDV6SE]

Thanks for the clarification, appreciate it.

[Discodicky]

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 suppose it may have been the dreaded brake light switch problem throwing it into neutral?
For the sake of $30 odd bucks it would be worthwhile changing anyway as it is known to be a pain.

[Tin Lizzy]

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 was guessing that cruise control would run away a bit on steep downhill, and HDC would slow me down too much??? Didn't consider combining them. I do like to feel that I'm in control of the descent when there's a house hooked up behind me though 😳

[Tin Lizzy]

I don't suppose it may have been the dreaded brake light switch problem throwing it into neutral?
For the sake of $30 odd bucks it would be worthwhile changing anyway as it is known to be a pain.

Good thought....It actually felt like the vehicle was in neutral when I was running along a very slight decline at the bottom of the mountain. I do carry a spare switch, but hadn't considered that.

[StewG]

When descending steep long hills like Cunninghams gap with my MY13 SDV6 towing a 2.5T caravan, I've generally used the paddles and sometimes in Sport and generous use of the brake when needed. The Redarc (not Tow Pro) would be set a touch higher than normal to get the caravan brakes doing their fair share. I've never had an issue with warning lights or anything else. I often use cruise control, but find it a nuisance on roads when close concentration (of the driver) is needed, such as tight curves followed by short straight stretches. Besides that, cruise control does tend to run away on downhill stretches. The only time I had a problem is when the RH inlet manifold split and the D4 went into cripple mode with all the power of an obese Fiat 500. It was downright embarrassing to travel about 100 km doing 100 kph downhill and 40 kph up hill with a string of traffic behind. And yes I pulled over wherever I could to let them overtake.