I just finished my build of the Caterpillar bulldozer D11 (set 42131) and I'm NOT able to operate it with the Control+ app on my iPhone.

First the calibrate process begins:

  • Step 1 in that is to move the scoop up and down, but instead the plough moves.
  • Step 2 is supposed to change the angle of the scoop, but nothing happens at all. The Control+ app just keeps playing that engine noise and absolutely nothing happens for minutes until I kill the app.

That is all. Without getting through calibration the model can't be operated.

Obviously I could have wired the 4 motors to the wrong sockets on the control box, but I'm absolutely certain I followed the instructions in the book correctly.
I double and triple checked at that point in the build as I found the pictures in the book not very clear at first. I'm VERY certain I got that right.
Even if I did get the motors mixed up I still expect to see some movement when trying to calibrate. But movement on the wrong parts.

Is there a known issue with the Control+ app for this set? (It works fine, using the same iPhone, with the 42100 Liebherr 9800 excavator set.)

Or do I really have to take the entire thing apart again to get at the wiring? It is really buried deep inside the model so that would be a real pain.

  • 1
    I don't want to say you should have another look at your wiring, but the fact that Step 1 is operating different set of motors than expected there is high chance wrong port might have been used on PUP Hub.
    – Alex
    Commented Oct 7, 2021 at 13:22
  • @alex I really can't see how I would have made any mistakes. The instructions on step 178/179 (main pictures) are not immediately obvious which port on the hub is B and which one D (I find the embossed lettering on the hub impossible to read when it is build inside the model), but the insert detail pic on step 179 makes it very clear. Step 198 even makes it more clear with the top-side view. I have to admin I didn't do a test-run at that point, because my phone battery was empty.
    – Tonny
    Commented Oct 7, 2021 at 13:33
  • 1
    I went through instructions to understand how this thing works. I think issue isn't related to cabling (it would be much easier to fix) but to gearbox. There are several places that could get things wrong if not paid much attention and assembled incorrectly and I can see why it needs calibration. It seems that assembled model's default setup is to control plough indeed, which fit your description. But don't have any suggestions what needs fixing, apart from checking each and every tan colored 12T gear, to confirm if their position is correct. Mismatch would result in not operating function.
    – Alex
    Commented Oct 7, 2021 at 15:12
  • 1
    @Alex I spend an hour last night pouring over the instructions and I came to the same conclusion. It seems that clutch system is more likely the cause of the problem than the wiring. I'll try to reverse the assembly into the various sub-module stages all the way back to stage 2 this weekend. It would at least save me from having to rebuild every sub-module. Only undo/redo the parts that provide the connections between the modules or build on top of them.
    – Tonny
    Commented Oct 8, 2021 at 9:42
  • 2
    @Alex If you would care to convert your last comment into an answer I will accept it. You were spot on. I disassembled back until step 120 and then found that the positioning of the 2L was 90 degrees off. I must have accidentally turned it during the initial assembly.
    – Tonny
    Commented Nov 9, 2021 at 14:47

2 Answers 2


Converting my last comments into an answer.

I went through the instructions to understand how this thing works. I think your issue isn't related to cabling (it would be much easier to fix) but there is something wrong inside the gearbox. There are several places that could get things wrong if enough attention has not been paid and it was assembled incorrectly. And I can see why it needs calibration. It seems to me that assembled model's default setup is to control the plough indeed, which fits your description.

Check steps 117 and 120 if you have assembled correctly. The thing is that one of the two pictured motors switch between functions and the other motor operates functions. Your issue seems to be related to the switching between functions, not its operation. Position the model in such a way that you can observe what is going on with orange 2L beam placed in step 117 and try calibration again. As far as I understand the "switch" motor has to turn this beam 90 degrees up (from pictured position) to enable 1st function (that is the blade); 180 degree (opposite direction from pic) for 2nd function.


I had the same problem as you and solved it. For me, the error is in step 87. I had mounted the orange part in the wrong side and it jammed the whole system from turning right.

Step 87

Hope this is useful to you!

  • Welcome to Bricks.SE! Thanks for sharing your solution.
    – jncraton
    Commented Mar 22, 2022 at 13:01
  • This was my mistake too. Thanks
    – Lunatik
    Commented Dec 26, 2022 at 22:55

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