DCT fault??

[Guest machinman]

Got a strange fault reared its head recently.

I use manual mode only on my 15 X DCT, 24000 miles.

At a Constant 15mph in 2nd gear the -button won't allow a change to 1st gear.

However, if you slow down to 11ish mph it changes to 1st on its own.

Have cleaned multi plugs etc.

Fine otherwise.

[Mike5100 2,061]

Surely that's normal?

It isn't a true manual in that it will always change down if it thinks it needs to, but it will trigger the rev limiter if you stay in one gear for too long while accelerating.

Is 15mph in first too close to the rev limiter so it won't let you change?

Mike

[DaveM59 1,605]

The DCT will not allow shifts if it calculates the RPM will be too high, and also does not allow you to bog and stall so will shift down to prevent this. Try it faster in a higher gear it will also shift down if you don't as speed falls. It doesn't work the other way though and will allow you to hit the limiter although I wouldn't be surprised if it also didn't shift up after a period of limiter hitting, if you were daft enough to keep it there. Never tried it and I bet no one else has!

[Guest machinman]

Thanks fellas for your thoughts. I failed to mention this is a intermittent problem, but getting more frequent. Surely 15/20mph should be ok from going from 2nd to 1st using the paddles and im sure I've done it plenty of times in the past.

Also, I've noticed in 1st sometimes their is zero engine breaking and other times plenty of engine breaking. Could it be related?

[Guest Hati]

Why don't you test D and S mode to see where the "factory" shift points are? To me it sounds like your expectations are different to what the DCT box is programmed to do. Try for an objective test in the two auto modes and let us know what you get.

[Guest machinman]

23 minutes ago, Hati said:

Why don't you test D and S mode to see where the "factory" shift points are? To me it sounds like your expectations are different to what the DCT box is programmed to do. Try for an objective test in the two auto modes and let us know what you get.

Will do and feed it back.

[fred_jb 10,269]

5 hours ago, machinman said:

Thanks fellas for your thoughts. I failed to mention this is a intermittent problem, but getting more frequent. Surely 15/20mph should be ok from going from 2nd to 1st using the paddles and im sure I've done it plenty of times in the past.

Also, I've noticed in 1st sometimes their is zero engine breaking and other times plenty of engine breaking. Could it be related?

It's a while since I had my DCT, but I had the optional foot shift fitted and found that very useful for overriding the DCT, particularly for downshifting.  I think I know what you mean about the engine braking being variable.  I think it depends on the particular situation, but I sometimes felt that the clutch disengaged for longer than necessary on a downshift, particularly when going downhill, leading to a momentary feeling of free fall.  Might be worth you running the DCT reset process.

Edited June 26, 2017 by fred_jb

[ste7ios 469]

It seems that on long downhills you may loose engine braking. I guess it disengages the clutch. In that case it needs a little twist of the throttle to engage it again...

[Guest machinman]

I varied the journey home tonight and found a distinct pattern. As I said I only use manual mode. I tried D&S and they seemed fine, changing up and down as expected. No problems their.

In manual mode I can paddle down 2nd to 1st at 25 mph no probs.

The problem only occurs on an uphill gradient. Unable to go from 2nd to 1st at any speed above 11/12 mph.

Unable to go from 3rd to 2nd unless it's at the speed where it changes by default.

Only occurring on uphill gradient under load, works fine on non gradient with or without load.

I called in at the  dealer and he suspect solenoid probs ☹

[Mikdent 4,070]

2 hours ago, ste7ios said:

It seems that on long downhills you may loose engine braking. I guess it disengages the clutch. In that case it needs a little twist of the throttle to engage it again...

 

I doubt very much that the clutch disengages on a downhill run, that would be dangerous. 

[ste7ios 469]

It happened to me, 2-3 times on a trip, on a very long downhill, where the "road" was muddy and very slippery (it was like riding in yogurt!). I was using only 1st and 2nd gear during this downhill... Suddenly I felt the bike free... There was no engine brake at all. Twisting a little the throttle and it was ok again.

 

In that situation 'slippery' may be the explanation.

[embee 7,288]

3 hours ago, machinman said:

I called in at the  dealer and he suspect solenoid probs ☹

No. The solenoids are clearly working fine when instructed to do so. For whatever reason the DCT ECU is deciding not to issue the instructions, whether that's by design or fault is another question.

[embee 7,288]

2 hours ago, ste7ios said:

It happened to me, 2-3 times on a trip, on a very long downhill, where the "road" was muddy and very slippery (it was like riding in yogurt!). I was using only 1st and 2nd gear during this downhill... Suddenly I felt the bike free... There was no engine brake at all. Twisting a little the throttle and it was ok again.

 

In that situation 'slippery' may be the explanation.

It could be that the rear wheel was reducing speed (slipping) to the point that as far as the DCT was concerned it was coming to a standstill so disengaged the clutch. Once this happened the wheel began to turn at road speed again, and when you opened the throttle it took up the drive as normal. Just guessing .......

 

It certainly doesn't go into freewheel mode on normal surfaces until you reach a very slow speed to avoid engine stalling.

[Guest Hati]

Stuart: if you travel the same road section this behaviour happens in manual mode, in one of the auto modes, do you experience the same issue?

[ste7ios 469]

@embee: My guess too. My engineer had no idea...