FANUC SRVO-402 Alarm: DCS Cart. Pos. Limit Explained
What SRVO-402 means
FANUC controllers display this fault as SRVO-402 DCS Cart. pos. limit (No.%d:%s, G%d, M%d) %02x. The message is generated by Dual Check Safety Cartesian Position Check logic on R-30iA, R-30iB, and R-30iB Plus controllers. The first parameter identifies the Cartesian Position Check number and its configured comment. G identifies the motion group involved. M identifies the model being checked: model 0 is the robot itself, while other model numbers point to a user-defined model such as a tool or fixture. The trailing hex value is a status field for the check. When the check detects that the monitored model has moved outside its configured safe Cartesian zone, DCS removes or blocks motor power to the affected group. The robot is left with no motor power on that group until the position is corrected and the alarm is properly cleared.
Common causes of the fault
Before assuming a hardware fault, check these causes in order of likelihood:
- The robot was jogged or a program ran a point beyond the configured Cartesian boundary — the most common cause.
- A program was edited or a position retaught, moving the robot outside a safe zone that was previously valid.
- A new tool, fixture, payload, or other user-defined model extends past the configured zone even though the wrist center looks fine.
- The Cartesian zone was configured too tightly for the actual process, causing repeated trips right at the boundary.
- The DCS frame, zone geometry, group assignment, model selection, or model dimensions are set incorrectly.
- A collision, shifted fixture, changed cell layout, or swapped tooling made a previously valid DCS setup unsafe.
Related alarm codes to check alongside SRVO-402:
- SRVO-404 DCS Joint Position Check — a monitored joint, rather than a Cartesian zone, is outside its configured safe range.
- Other DCS position or speed check alarms — indicate a configured position or speed limit was exceeded, cutting motor power in the same way as SRVO-402.
Step by step troubleshooting
Work through these steps before touching the DCS configuration:
- Record the full alarm text exactly as displayed, including the check number, comment, group, model number, and hex status.
- Lock out and tag out per your site procedure if any inspection requires entering the robot’s safeguarded space.
- Open the DCS screen and find the Cartesian Position Check entry flagged unsafe; note its configured zone and which model it monitors.
- Use the DCS visualization, if available, to compare the configured zone against the current robot and model position.
- Compare the model number in the alarm — 0 for the robot, other values for tooling or fixtures — against the physical setup on the machine.
- Check for recent program edits, retaught points, tooling changes, or cell layout changes around the time the alarm started.
- Inspect for any collision, shifted fixture, or bent tooling that would place the robot or model outside the zone even at a previously good position.
Clearing and resetting the alarm
Recovery from SRVO-402 is documented as a jog-back procedure, not a simple reset button:
- Switch the controller to T1 mode and enable the teach pendant.
- With the alarm displayed, press and hold SHIFT and press RESET to permit recovery from the DCS position violation.
- Keep SHIFT held and jog the robot in the direction opposite the boundary violation, using WORLD coordinates and the relevant Cartesian axis for the identified check.
- Do not release the key combination before the robot is back inside the configured safe zone — the alarm can return if you let go early.
- Once the robot is inside the zone, release the keys and confirm the alarm stays clear.
If SRVO-402 reappears immediately, stop jogging and inspect the DCS Cartesian Position Check configuration, frame, zone dimensions, group, and model instead of repeating the reset. Changing or disabling a DCS check is a safety-function change, not a routine reset, and requires the applicable FANUC safety procedure, risk assessment, authorization, and validation.
When it points to a hardware failure
SRVO-402 is a safety-position violation. By itself it is not evidence of a failed servo amplifier, motor, pulsecoder, or feedback cable. Confirm the DCS configuration and physical cell geometry first, then look at hardware only if independent symptoms support it.
Signs that point toward a hardware problem instead of a configuration or boundary issue include a companion servo alarm — such as a pulsecoder, encoder, or fuse-related fault — appearing alongside or instead of SRVO-402, position feedback that does not match the physical robot position, an axis that will not hold position once inside the safe zone, or intermittent position error that tracks with cable movement or connector position rather than with programmed points. A loose or damaged cable or connector at the amplifier or motor end can produce erratic feedback that resembles a position violation. If these companion symptoms are present, treat the pulsecoder, cable, amplifier, or motor as suspect and test each independently of the DCS configuration.
How Robotics Integration helps
Robotics Integration supports maintenance teams working an active SRVO-402 alarm on FANUC R-30iA, R-30iB, and R-30iB Plus controllers. We help by phone or remote session to read the full alarm text, walk through the DCS Cartesian Position Check screen, and identify whether the alarm points to a boundary issue, a tooling or fixture change, or a configuration problem versus a hardware symptom.
When the cause turns out to be hardware — a pulsecoder, feedback cable, amplifier, or motor — we repair and test those components, and we can send a technician on-site to inspect the cell, verify DCS zone and model settings against the physical layout, and get the robot back in production. We work from the alarm history and cell details you provide rather than guessing at the configuration.
Looking up a different code? See the full FANUC and robot alarm code list, or read about our FANUC robot repair.
What to send before you call
Before you call, gather the controller model (R-30iA, R-30iB, or R-30iB Plus), the complete SRVO-402 alarm text including the check number, comment, group, model number, and hex status, the axis or group involved, and what the robot was doing when the alarm hit — jogging, running a program, or idle. Note any recent program edits, retaught points, tooling changes, or collisions, along with the recent alarm history if the fault has repeated.
Call 1-602-449-1556 and have that information ready. It lets us tell quickly whether you are dealing with a boundary or configuration issue you can clear yourself or a hardware fault that needs component repair or an on-site visit.
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