What Is CAN Bus? Working Principle, Structure, and How to Check Errors on Electric Forklifts

🔹 1. What is CAN Bus?

CAN Bus (Controller Area Network) is a high-speed communication system that allows different controllers in an electric forklift to exchange information using just two wires:
👉 CAN_H (High) and CAN_L (Low).

This technology is widely used in electric forklifts, cars, trucks, and industrial robots, enabling stable, accurate, and efficient data transmission with fewer cables.

For example, on EP or Heli electric forklifts, the CAN bus connects the main controller with:

Steering controller
Lift controller
Display unit
Lithium battery BMS

🔹 2. CAN Bus Structure on Electric Forklifts

A typical CAN bus network includes:

Component	Description
CAN_H & CAN_L wires	Twisted pair cables to reduce noise.
120Ω termination resistors	Two resistors at both ends of the bus stabilize signals.
End devices	Controller, Display, BMS, Motor driver, etc.
Power source	Usually 12V, 24V, or 48V DC.

Basic diagram:

🔹 3. Working Principle of CAN Bus

CAN bus uses differential signaling to transmit data:

When sending data: CAN_H rises to ~3.5V, CAN_L drops to ~1.5V
When idle: both lines sit around 2.5V

This ensures:
✅ High noise immunity
✅ Stable communication
✅ Reliable performance even near motors and in harsh environments

🔹 4. Advantages of CAN Bus System

Advantage	Explanation
Fewer wires	Only two wires are needed for multiple devices.
High speed & stable	Fast and noise-resistant communication.
Automatic fault detection	System detects short, open, or hardware faults.
Multi-device communication	Many modules can share the same bus line.

🔹 5. Symptoms of CAN Bus Faults

Symptom	Possible Cause
Display shows no data	Lost connection between Display and Controller
“CAN Error” or “No Communication”	Short or open circuit in CAN lines
Forklift won’t start	No CAN communication signal
Data flickers or freezes	Noise or reversed CAN_H/CAN_L wiring

🔹 6. How to Check the CAN Bus

🔸 Step 1: Check termination resistance

Turn off key switch (Key OFF)
Measure resistance between CAN_H and CAN_L
✅ Normal value: ≈ 60Ω

120Ω → missing one resistor
0Ω or ∞ → short or open circuit

🔸 Step 2: Measure voltage when powered on

Turn on key (Key ON)
Measure voltage of each line to ground:

Line	Normal value
CAN_H – GND	2.5V ~ 3.5V
CAN_L – GND	1.5V ~ 2.5V
CAN_H – CAN_L	≈ 2V

If voltage doesn’t fluctuate → communication error.

🔸 Step 3: Check wiring continuity

Test continuity between CAN wires at both ends
Resistance ≈ 0Ω → good
OL or high → open circuit
Very low between CAN and GND → short to ground

🔹 7. Technician Tips

✅ Measuring resistance between CAN_H and CAN_L is the quickest diagnostic method.
✅ There should only be two 120Ω resistors — one at the controller, one at the display.
✅ Always use twisted pair cables for CAN wiring.
✅ Avoid running CAN cables alongside power lines.
✅ Never install more than two termination resistors.

🔹 8. Conclusion

The CAN Bus system is the communication backbone of every electric forklift.
Understanding its structure and diagnostic methods helps technicians find faults faster, repair accurately, and reduce downtime.