Terminations resistances

About the use of resistors, I would like to know which kind of problems we can cause on adding an additional 120 ohms resistance on the bus?

If this resistence is introduced on the "main line" or on the nodes?

Some CAN devices can't drive the current required if the total resistance is too low (ie, you add to many terminating resistors). I had a customer yesterday with the problem adding an Aim SmartyCam with built-in CAN termination to a Lamborghini Super Trefeo race car. The proper location of the termination resistor is one 100 - 120 ohm resistor at each end of the CAN bus. Often a simple 2-node bus will operate with only a single resistor on the bus.

The symptom is messages that aren't received, or devices that see too many errors so they stop transmitting.