CAN L and CAN H wires are connected reversely

When the CAN L and CAN H wires are connected in reverse, generally, the control module that is connected in the wrong way will not be able to communicate, while the communication of other control modules is normal. The schematic diagram of the reverse connection of the CAN L and CAN H wires is shown in the figure below.

Measure the voltage at the CAN wire pin of the suspected control module to verify whether the voltage is normal. Check the line connection with the CAN network diagram to determine whether this fault exists. If so, repair the CAN network. Replace the control module involved in the fault code content to determine whether the fault is caused by this control module.

CAN L open circuit

When the CAN L wire of a control module is broken, the control module will not be able to communicate, but other control modules can still communicate. The fault code of this faulty module may be read in other control modules. If the CAN L wires of multiple control modules are broken, the communication functions of these control modules will be affected.

If the faulty control module has a terminal resistor, the resistance measurement method can be used to determine. Measure
the resistance between CAN H and CAN L of the diagnostic interface. If it becomes 120Ω, it means that one of the terminal resistors is broken. If the faulty control module does not have a terminal resistor, it is necessary to measure the conductivity of the CAN wire of the control module. The bus waveform of CAN L broken circuit is shown in the figure below.

Replacing the control module involved in the fault code can quickly determine whether the fault is caused by the control module itself. In addition, it is necessary to find the breakpoints in conjunction with the network diagram to accurately find the cause and eliminate the fault.