RSC-HMU [CAN DOWN] Message, No Data Displayed, How to Resolve

The controller is displaying a [CAN DOWN] message on boot

When the controller starts up, it will display a CAN DOWN message if the CAN link tot he CFFB is not working. When this happens, the engine will not be cranked. The CFFB fan will still operate, as the output for the fan does not use the CAN link, it uses a separate relay.

If the CAN link is restored, the controller will regain its functions, as per this video:

How to fix the [CAN DOWN] message?

To fix the [CAN DOWN] message, you need to correct the CAN link between the controller and the CFFB, in one or more of the following ways.

1) The CFFB is unplugged

Replace the plug back into the CFFB.

2) The CAN cable between the CFFB and the controller is broken

Trace the CAN cable between the controller and the CFFB. If the cable is broken, replace it.

The cable is a green and white twisted pair, as showing in the image below, going into the CFFB connector. These go into the RSC-HMU controller connector on pins 24 and 25.

3) The CFFB has failed

If you remove the cover from the CFFB, you can see the board with two lights flashing. These two lights indicate the boards status. The left hand light should be solid, showing the board is powered up. The right hand light will flash to show the processor is operating correctly. See the video below for the lights to check the status.

If the power light is on, but the CPU light is not flashing, replace the CFFB.

If the power light is off, you can check the power supply (12V) to the CFFB. If restoring the power to the CFFB does not work, replace the CFFB.