14. Troubleshooting

Version 1.2Software: FuelTech Vision 3.0Firmware: 00.03.00.01Products: FT700, FT470, VisionFT2026-10-13

#Diagnostic tools

Diagnostics Panel > CAN ports: one column per port, with the channels that are arriving over CAN and whether they are active or stalled.
CAN Sniffer (Tools > CAN Sniffer): shows the real traffic of the port.
CAN Network (Tools > CAN Network): lists the FuelTech devices the VCU found.
Diagnostic channels (in the VCU channel list): CAN: Bus load A/B/C (port occupancy in %, calculated every second, adding what comes in and what goes out), CAN: Bus Off (one bit per port turned off by error) and Custom CAN: Frame error (one bit per frame with an error).
VCU notifications: warnings such as "Communication error - CAN A", "CAN A: Bus error", "Error initiating Can port A" and "CAN A Disabled".
Configuration alerts (Diagnostics Panel, Configuration alert validation window): the map validation warns about a frame with more than 8 bytes on a port without FD mode, a signal with Arithmetic channel off and a fractional scale or negative offset, and PWC controls (personal watercraft, jet ski) with the vehicle port off or not in RAW mode.
Multimeter: resistance between CAN_H and CAN_L with everything off (about 60 Ω).

#Symptoms, causes and solutions

Symptom	Probable cause	What to do
Nothing arrives: the channel stays at zero and the sniffer does not show the ID	Port off; mode or rate different from the module's; CAN_H and CAN_L swapped; module without power; module on another port	Check CAN ports (port on, mode, rate). Measure the 60 Ω. Check the wiring and the module's power. On the FT700, test the other ports in the sniffer.
The sniffer shows the ID, but the channel stays at zero	Bytes of the RX frame greater than the real size; ID different from what the module transmits; Direction still TX after importing a DBC; frame or function off; frame disabled by an error	Set Bytes to the size seen in the sniffer. Check the ID and the Direction. See the "Custom CAN: Frame error" channel.
Nonsensical value, very large or jumping around	Byte order swapped; wrong Start bit; wrong signed/unsigned setting	Swap Intel/Motorola. Redo the position from the DBC. Check the Value type.
Value stuck at the offset or at zero, with no error	Arithmetic channel off with a scale below 1	Turn Arithmetic channel on.
The value drops to zero from time to time	Timeout too short for the sender's period	Use a Timeout of at least three times the sender's period and never less than 0.5 s.
Value one step lower than expected	The VCU truncates the raw value when transmitting	If the receiving equipment lets you choose the scale, use a finer one (0.1 instead of 1) and the same one on both sides: Scale and Offset in the VCU must match the receiver's. If it does not, use the scale the equipment specifies: the truncation is normal.
The third-party equipment receives nothing	Standard vs extended ID swapped; wrong port or rate; FD frame to classic equipment	Check Extended ID and the port. On an FD port, turn on Force classic CAN in the frame.
"Communication error - CAN A" notification	The VCU cannot transmit on the port. Two causes: a port checked in Alerts > Error in the CAN port with no acknowledgment of the frames for longer than the time for validation; or a failure of the port itself, which the VCU restarts in about 1 s	Check whether another module is connected and powered, the rate and the wiring. If the port is not checked in the alert, the cause is the port failure: check the electrical connections and the harness.
"CAN A: Bus error" notification	Excessive errors (bus-off): different rate, wrong termination, swapped or shorted wires	Measure the termination, check the rate of all modules and the wiring.
"Error initiating Can port B" notification	FD mode on a port that does not support CAN FD, or invalid rate	Turn FD mode off (see which ports accept FD in the ports chapter) and turn the VCU off and back on.
"CAN A Disabled" notification	The port is off in CAN ports	If the port should be in use, turn it on, then turn the VCU off and back on.
FuelTech device does not appear in CAN Network	Port in RAW mode; port off; termination; two identical devices with the same identification on the network	Set the port to FTCAN 2.0, turn it on, then turn the VCU off and back on. Check the termination and the identification of each device.
You changed the rate, mode or terminator and nothing changed	The port is only reconfigured at power-up	Write the map, turn the VCU off and back on.
CAN: Bus load above about 70% (rule of thumb)	Heavily loaded bus: delays and lost frames. Without acknowledgment of the frames the load also appears high	Increase the periods, turn off what is not used, move devices to another port.