please hepl czech republic detroit 60 ddec3

I may be not understanding: The sensor wire might have a break under the insulation. Hook up a test light and wiggle it to see if it loses continuity.

 

I may not totally understand you. Does it not have two sensors on the left front of the engine on different gears? Both were replaced?
If you have changed everything electrical, even the harnesses, and the problem stays with the truck maybe it is not electrical.
I had a problem with a 14 L gear train that did something like that.
If that is the case others on here know much more about them than I.
Try to keep your questions short direct and clear. I understand you are using a second language.

 

All I know is there’s 2 speed sensors on my Truck. One on bottom, another on top.

 

On the 14L there is a gear set in the front. Two gears on a common shaft with a dowel pin between them. When that dowel is damaged it can allow the two gears to change position a bit. They most often change on start up or when you shut it off. It also would change some times while driving.
I do not thank the small difference in timing would have been a big problem. However the computer trying to compensate for the sensor readings that did not correspond caused a lot of problems.
If you send it to the wrong two shops you can figure that out for about $25,000 and no truck for seven weeks. Sounds a little bit like the hole in the DPF deal today.
So always ask. Will that fix it? Probably still end up with: Well do you want you truck back or not in the end.

 

1998 has to be either the last of 11.1 or a 12.7. No 14 L in 1998

 

So you have your problem figured out? What was the problem?

 

After looking at code 54 that is vehicle speed not engine.
I know nothing about your truck. What transmission is in it?
Had a problem with a Fuller once. The driveshaft yoke was a little loose. The tone wheel for the sensor could be turned with a screw driver, through the sensor hole. Everything looked fine. Tightened the yoke and no more problem.
Many vehicles have two sensors on the back of the transmission also.
I do not know the answer to your question but maybe someone else can be more helpful.
Can we get a picture of your tractor?