STEP 1: Physical Cable Check

Grumble through this part even though this is always what fixes it.

Actions:
– Power the unit off fully.
– Remove the shell and expose the battery compartment.
– Locate the Battery Extension cable running from the battery to CT4 board connectord CT4-3 & CT4-4.
– Disconnect and reconnect both ends firmly.
Inspect for: Bent or recessed pins, crimp failures, pinched insulation, corrosion, or frayed wire near the connector.

Expected outcome:
If the cable was loose, the error clears immediately on reboot.

STEP 2: Hard Reset the Battery Battery Communication Cable

Actions:
– Disconnect both main power connector and BEComm cable.
– Leave battery disconnected for 45–60 seconds.
– Reconnect power first, then reconnect BEC cable.
– Reboot robot.

Expected outcome:
If a BEC lockup was the issue, communication returns and the error disappears.

STEP 3: Measure Battery Voltage (Actual Multimeter Check)

Actions:
– Pull battery or access its leads.
– Use a multimeter to measure output.

• Normal range: 29–29.4V (fully charged)
• Typical operation: 26–28V
• Below 24V = battery trouble territory

If the voltage is normal, this rules out dead cell groups but doesn’t rule out BMS failure.

STEP 4: Cross-Battery Validation

This is the real decider in 95% of cases.

• Option A: Install a known-good battery. If the error disappears, the original battery’s BMS is bad.
• Option B: Place the suspect battery into a known-working CC1. If that unit throws the comm error, the battery is at fault.

If both A and B show good comms, the battery is fine — shift suspicion to the CT4 board.

STEP 5: Inspect CT4 Board (Powerboard)

Only do this after cable and battery validation.

• Burnt components
• Rainbow discoloration on transformer (overload)
• Blown MOSFETs
• Loose or corroded connectors
• Damage to BMS comm port

If CT4 shows abnormal behavior (0V output on CT4-3, no boot-up, or intermittent power), replace the board.

STEP 6: Replace CT4 Board

If the cable is intact, voltage normal, and cross-battery tests confirm comm loss through CT4, replace the CT4 board.
Reassemble, reboot, and confirm the error clears.

Additional Notes

• BoTs tipped over often yank this cable loose inside the frame.
• Deep discharge can lock Battery communication logic, requiring a hard reset.
• Water intrusion is a common silent killer of Battery communication boards.
• If the unit fails to boot even with the charger connected during this error, CT4 is the primary suspect.