How to Fix ABB ACS355 Fault F0035 Safe Torque Off (STO)

Dealing with Fault F0035 on your ABB ACS355? Here is the Fix.

If you are looking at your ABB ACS355 control panel and seeing F0035 flashing back at you, the first thing you should know is: Your drive likely isn't broken.

 

In the world of ABB machinery drives, F0035 stands for Safe Torque Off (STO). It is a safety function designed to prevent the motor from starting unexpectedly. While it shows up as a "fault," it is actually the drive doing exactly what it was designed to do—protecting people and equipment.

What is the F0035 Code Exactly?

The ACS355 has two safety input channels (STO1 and STO2). For the drive to run, both of these channels must receive a 24V DC signal. If either channel (or both) loses that 24V signal, the drive immediately cuts power to the motor and triggers the F0035 fault.

Common Reasons Why F0035 Appears

• Emergency Stop (E-Stop): Someone has pressed an E-stop button connected to the drive.
• Safety Relay Tripped: A safety gate is open or a light curtain has been interrupted.
• Loose Wiring: The wires at the X1C terminal block (the orange/yellow connector) have vibrated loose.
• Missing Jumpers: On a new drive installation, the factory-installed jumper wires are missing or weren't replaced by a safety circuit.
• Power Supply Issue: The 24V DC source powering the safety circuit has failed.

Step-by-Step Troubleshooting

1. Check Your E-Stops and Safety Gates

Before touching the drive, check the machine. Is an Emergency Stop button pushed in? Is a safety door open? Reset your safety devices first. In 90% of cases, resetting the physical E-stop button clears the F0035 fault.

2. Inspect the X1C Terminal Block

Look at the bottom of the ACS355 control unit. You will see a small, usually yellow or orange, terminal block labeled X1C.

• Terminal 1 (24V): This is the internal 24V source.
• Terminal 3 (STO1) & Terminal 4 (STO2): These must both have 24V for the drive to run.

If you aren't using an external safety relay, there should be jumpers connecting Terminal 1 to Terminals 3 and 4. If these are loose, F0035 will trip.

3. Measure with a Multimeter

Set your meter to DC Voltage. Measure between Terminal 2 (GND) and Terminals 3 and 4.

• If you see 0V, your safety circuit is open.
• If you see 24V but still have the fault, try cycling the power to the drive.

4. Check Parameter 3025 (STO Operation)

Did you know you can change how the drive reacts to the STO signal? Go to Parameter 3025:

• If set to FAULT (1), the drive trips with F0035 and requires a manual reset.
• If set to ALARM (2), the drive will show a warning but will start automatically as soon as the 24V signal returns.

Note: Always follow your local safety regulations before changing how a safety circuit behaves!

How to Reset Fault F0035

1. Restore the 24V DC signal to terminals 3 and 4 (close the E-stop or safety gate).
2. Press the RESET button on the drive keypad.
3. If the drive is in "Remote" mode, you may need to cycle the start signal from your PLC.

Summary

The ABB ACS355 F0035 fault is all about safety. It's a sign that the drive’s "Safe Torque Off" circuit has been broken. Whether it's a pressed E-stop, a loose wire on the X1C connector, or a missing jumper, the fix is almost always found in the wiring rather than the drive hardware itself.

Still can't get your ACS355 to start? Let us know in the comments if you are using an external safety relay or just the internal jumpers, and we can help you narrow it down!