CAN bus 120 ohm resistor questions

[Hicham M]

Hello,

I have a vehicle equipped with CAN bus, and based on it's schematic, this vehicle has many control units equipped with CAN bus, 2 control units have a 120 ohm resistor, which is normal.

I have a custom electronic board that has A CAN bus, and have a 120 ohms between CANH and CANL inputs of this board. I mounted this board on the vehicle and everything worked fine for couple of months before the driver started noticing some weird behaviours in the accessory controllers when my board is connected to the vehicle.

I discovered recently about this internal resistor, could this be the problem ?

And does anyone here knows how to diagnostic this kind of problems ?

thank you

 

[FvM]

CAN bus is designed as a party line with termination resistors at both ends. Placing more termination resistors is not correct, one additional resistor would typically not cause bus failure.

 

[Hicham M]

CAN bus is designed as a party line with termination resistors at both ends. Placing more termination resistors is not correct, one additional resistor would typically not cause bus failure.

Thank you FvM,

Will it damage the system with time ?

 

[FvM]

CAN bus transceivers can withstand even a bus short. No problem in this regard.

 

[ravindragudi]

The local 120 ohm termination resistor on CAN bus for the module is mainly meant for testing in the lab with CAN simulator. This should not go into the vehicle system. Under normal CAN traffic conditions, there may be no functional problems. But if the CAN traffic goes high this particular module may misbehave and apparently cause further increased traffic on the bus.

 

[Hicham M]

The local 120 ohm termination resistor on CAN bus for the module is mainly meant for testing in the lab with CAN simulator. This should not go into the vehicle system. Under normal CAN traffic conditions, there may be no functional problems. But if the CAN traffic goes high this particular module may misbehave and apparently cause further increased traffic on the bus.

that makes sense, Is there a away to prove that beside doing heavy tests on the vehicle ?

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CAN bus transceivers can withstand even a bus short. No problem in this regard.

You mean even if I connect the CANH and CANL low to the ground ? the bus will work ?

 

[FvM]

You mean even if I connect the CANH and CANL low to the ground ? the bus will work ?

You asked about damage. Of course bus operation will be stopped while shorted.

 

[ravindragudi]

Other method of producing this failure would be use more than 2 of this modules on CAN bus ...