Rover 75 CAN-bus - how does it work?
Discussion
I'm fitting a hunter CB5 CAN-bus satnav interface module to a Rover 75.
My understanding of CAN-bus is that it's a single bus and all data from all devices reaches all parts of the bus.
The fitting instructions, however, recommend tapping into the bus at the automatic gearbox because this is the point where there will be least data.
I have tapped in on the twisted pair run between the ECU and key fob transponder. Having done this, the car no longer starts, even with all other wires on the CB5 disconnected. Removing the two can bus wires allows the car to start as normal. This is particularly amusing since the installation/troubleshooting comments that 'the CB5 is very high impedance, and only reads data from the bus, so can have no affect on the car'
How does it work?
My understanding of CAN-bus is that it's a single bus and all data from all devices reaches all parts of the bus.
The fitting instructions, however, recommend tapping into the bus at the automatic gearbox because this is the point where there will be least data.
I have tapped in on the twisted pair run between the ECU and key fob transponder. Having done this, the car no longer starts, even with all other wires on the CB5 disconnected. Removing the two can bus wires allows the car to start as normal. This is particularly amusing since the installation/troubleshooting comments that 'the CB5 is very high impedance, and only reads data from the bus, so can have no affect on the car'
How does it work?
garyyb said:
I'm fitting a hunter CB5 CAN-bus satnav interface module to a Rover 75.
My understanding of CAN-bus is that it's a single bus and all data from all devices reaches all parts of the bus.
The fitting instructions, however, recommend tapping into the bus at the automatic gearbox because this is the point where there will be least data.
I have tapped in on the twisted pair run between the ECU and key fob transponder. Having done this, the car no longer starts, even with all other wires on the CB5 disconnected. Removing the two can bus wires allows the car to start as normal. This is particularly amusing since the installation/troubleshooting comments that 'the CB5 is very high impedance, and only reads data from the bus, so can have no affect on the car'
How does it work?
While I am no expert on the Rover 75, there may be several different buses on the vehicle running at different speeds, if you didn't 'tap' into the correct one then it will cause problems.My understanding of CAN-bus is that it's a single bus and all data from all devices reaches all parts of the bus.
The fitting instructions, however, recommend tapping into the bus at the automatic gearbox because this is the point where there will be least data.
I have tapped in on the twisted pair run between the ECU and key fob transponder. Having done this, the car no longer starts, even with all other wires on the CB5 disconnected. Removing the two can bus wires allows the car to start as normal. This is particularly amusing since the installation/troubleshooting comments that 'the CB5 is very high impedance, and only reads data from the bus, so can have no affect on the car'
How does it work?
Additionally not all the same data is transmitted on the same buses and so the information required may not be present.
Given you are attempting to access data on what would be considered the secure data transmission:
1. It may not be CAN communication.
2. If it is the protocol will most certainly not be standard and may contain methods of detecting 'tap' devices to prevent 'crackers'.
The CANBus must have a wire to wire impedance of 60ohms. (They are connected at either end with 2 120ohm resistors in parrallel so 60ohms.)
Have you tried disconnecting the device to see if the ability to start the car is restored?
I would recommend following the instructions.
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