Truck CAN J1939 Protocol

Hello all of you I am new here on the forum and first of all I want to say 'whowww' what a brilliant forum.

Sorry I'm writing in English; my German is like that of Rudi Carel, a fellow Dutchman. I have no problem reading written German, so please don't hesitate to answer me in German.

My question is specific to trucks. I'm working on a project where I need to reduce the maximum torque, preferably using a CAN command. Currently, I'm using a truck tuner that modifies the torque limiter in the truck's ECU. Our ECU supports CAN 2.0 B, which we use to read CAN engine messages. I know that it's possible to enter a second engine torque map into the engine's ECU, and I believe it's related to PGN 65251.

My question: is there someone who know how to write these points into the ECU and how to switch between them?

Please help me, my project is stalling at the moment.

Cees.

Hi Raysigher,

In the context of programming and developing SAE J1939 devices, I had to delve into the subject – it was very interesting.
I'll reach out to some former colleagues about this, but I can't say how successful that will be.
Why do you say 'I think that it has to do with PGN 65251'?
Perhaps a silly question, but: What is a PGN 65251?

Best regards, Moses.

As I understand, this PGN only delivers information and cannot be used to 'program' the ECU.

pgn65251 - Engine Configuration - EC -
Transmission Repetition Rate: Triggered by a change in torque/speed points exceeding 10% since the last transmission. Alternatively, or every 5 seconds.
Data Length: 34 bytes.
Data Page: 0
PDU Format: 254
PDU Specific: 227
Default Priority: 6
Parameter Group Number: 65251 (00FEE3 16)
Bit Start Position / Bytes Length SPN Description SPN
1-2 2 bytes Engine Speed at Idle, Point 1 (Engine Configuration) 188
3 1 byte Percent Torque At Idle, Point 1 (Engine Configuration) 539
4-5 2 bytes Engine Speed at Point 2 (Engine Configuration) 528
6 1 byte Percent Torque At Point 2 (Engine Configuration) 540
7-8 2 bytes Engine Speed at Point 3 (Engine Configuration) 529
9 1 byte Percent Torque At Point 3 (Engine Configuration) 541
10-11 2 bytes Engine Speed at Point 4 (Engine Configuration) 530
12 1 byte Percent Torque At Point 4 (Engine Configuration) 542
13-14: 2 bytes - Engine Speed at Point 5 (Engine Configuration) - 531.
15 1 byte Percent Torque At Point 5 (Engine Configuration) 543
16-17: 2 bytes. Engine Speed at High Idle, Point 6 (Engine Configuration): 532.
18-19 2 bytes Gain (Kp) of the Endspeed Governor (Engine Configuration) 545.
20-21 2 bytes Reference Engine Torque (Engine Configuration) 544
22-23 2 bytes Maximum Momentary Engine Override Speed, Point 7 (Engine Configuration) 533.
24 1 byte Maximum Momentary Override Time Limit (Engine Configuration) 534
25 1 byte Requested Speed Control Range Lower Limit (Engine Configuration) 535
26 1 byte Requested Speed Control Range Upper Limit (Engine Configuration) 536
27 1 byte Requested Torque Control Range Lower Limit (Engine Configuration) 537
28 1 byte Requested Torque Control Range Upper Limit (Engine Configuration) 538
29-30 2 bytes Extended Range Requested Speed Control Range Upper Limit (Engine)
configuration)
1712
31-32 2 bytes Engine Moment of Inertia 1794
33-34 2 bytes Default Engine Torque Limit 1846