Resetting SINUMERIK 840D sl Fan Operating Time Alarm XLM_00 (2)

1. Problem Overview

On a DMG MORI MILLTAP 700 equipped with a SINUMERIK 840D sl controller (NCU 710.3 PN) and a SINAMICS S120 drive line-up, operators may see the following alarm after a long period of continuous service:

DP003.Slave003:XLM_00 (2): Power unit: Fan operating time reached or exceeded. 0.

The alarm originates in the Active Line Module (ALM), which is the line-side infeed of the SINAMICS S120 book-size or chassis drive system. The line module is a slave on PROFIBUS / PROFINET DP003, slave address 3, with the symbolic drive object name XLM (line module, X = axis-type identifier for infeed in SINAMICS parameter naming).

The alarm fires when the ALM's internal fan-hour counter crosses the configured service interval. The drive signals the alarm to the NCK, which surfaces it to the HMI as DP003.Slave003:XLM_00 (2). The (2) suffix indicates alarm class / acknowledgment type per the SINAMICS alarm numbering scheme (alarm class 2 = alarm, clearable).

2. Affected Components and Topology

2.1 Drive Object Layout

On a typical 840D sl with SINAMICS S120, the drive objects are addressed numerically:

• DO1 - Control Unit (CU320-2 PN)
• DO2 - Line Module (ALM) - symbolic name XLM in the NC machine data
• DO3, DO4, DO5, ... - Motor Modules (SVM, SPM, etc.)

The HMI displays the alarm as DP<bus>.Slave<addr>:<DO name>_<index> (alarm class). In this case the DO name is XLM and the alarm index is 00 with class 2.

3. Alarm Decoding: What XLM_00 (2) Means

The SINAMICS alarm 208500 "Power unit: Fan operating time reached or exceeded" is the underlying fault code that the NCK maps to the symbolic XLM_00 presentation. The fault value 0 in the HMI line is the default "no additional info" value. Refer to the SINAMICS S120/S150 List Manual, function diagrams and parameter lists for the canonical mapping.

The triggering condition is:

fan_operating_hours >= p0252[0]  (with p0251[0] being the active counter)

After acknowledgment and a fan replacement, the counter must be reset to 0 so the next interval starts fresh.

4. Root Cause: Why the Write to p0251 Fails

When the operator navigates to Setup → Machine data → Infeed parameter (manufacturer access level, password protected) and attempts to write p0251[0] = 0, the drive returns:

No write access with controller enabled.
Error on writing parameter 251[0] = 0.

This is not a permission problem with the HMI access level. It is a pulse / controller enable state problem. SINAMICS drive parameters that affect commissioning-relevant runtime behavior - including the service-interval counters in the line module - are protected against online write while the drive is in run state. The drive rejects the write because:

1. The NCK and the drive are exchanging cyclic PROFIdrive telegrams; pulse enable (r0002.0 = 1) is active on the ALM.
2. The infeed is in closed-loop control and actively regulating the DC link.
3. SINAMICS parameter management has a global rule: commissioning parameters (C parameters) and a defined set of motor/power-unit parameters can only be written when pulse enable is withdrawn and the access level is sufficient.

5. Preconditions for the Reset

To successfully reset p0251, all of the following must be true at the same time:

6. Step-by-Step Reset Procedure (Field-Validated)

The following sequence was used successfully in the field on a DMG MORI MILLTAP 700 with NCU 710.3 PN and reproduces the working procedure. Read the entire procedure before starting; the E-Stop must remain latched until the parameter write is confirmed.

1. Power on the machine in normal operating mode. Wait for the NCK and drive to complete their boot and the HMI to reach the operator screen.
2. Replace the ALM fan. On S120 book-size line modules, the fan is accessible from the front of the unit; on chassis, the fan is a sub-assembly in the top hood. Document the part number of the old and new fan in the maintenance log. The SINAMICS S120 List Manual and Equipment Manual for the specific ALM (e.g. 6SL3130-6/7TE series) identify the spare part.
3. Press the Emergency Stop button on the machine. This removes the controller enable (NE/NF contactor chain opens) and forces the ALM pulse enable to drop. The drive is now safe to write commissioning-class parameters.
4. On the HMI, navigate to: Setup → Machine data → Infeed parameter.
5. Log in with the manufacturer password for the infeed parameter screen. On DMG MORI machines this is typically the Siemens service password SUNRISE-style credential. The dialog switches to write-enabled.
6. Confirm the access level parameter p0003 is set to 3 on the ALM. If it reads 1, change it to 3 first and accept the value. (p0003 on the ALM is independent of the HMI display access level.)
7. Set p0251[0] = 0 (fan operating hours counter reset). The drive should now accept the write because pulse enable is withdrawn.
8. Optionally set p0252[0] to the desired next service interval (default is typically 30000 h on ALM fans; consult the Equipment Manual for the exact part). Many service engineers leave p0252 unchanged after fan replacement.
9. Verify the write succeeded. The parameter screen should show 251[0] = 0 without the "Error on writing parameter" message.
10. Clear the alarm on the HMI via the alarm acknowledge key (or via NCK Reset). The XLM_00 (2) alarm should clear once the counter is back below the interval.
11. Release the Emergency Stop and run a controlled return-to-home / reference sequence on the machine before resuming production.

7. Parameter Reference

For DO numbering and parameter index conventions, see the SINAMICS S120/S150 List Manual and the SINUMERIK 840D sl Commissioning Manual. The parameter list is published in the Siemens Industry Online Support under entry ID 109746340 and is updated by firmware; confirm with the FW version on the specific CU320-2 (e.g. V5.2, V5.3, V6.x for S120) when reading thresholds.

8. Verification

After releasing the E-Stop, perform the following checks before returning the machine to production:

1. Alarm cleared: HMI alarm bar shows no active DP003.Slave003:XLM_* entries. Historical alarm log retains the entry, which is correct for traceability.
2. Counter value: In the infeed parameter screen, p0251[0] reads 0 (or a small value representing time since the reset, depending on how quickly the machine was restarted).
3. DC link ramp: Issue a controlled power-on and observe the DC link voltage (r0070) settling at the expected ALM setpoint (typically 600 V on 380-480 V mains, 720 V on 500-690 V mains) without oscillation.
4. Fan operation: Visual or tactile confirmation that the new fan is running and that intake air is unobstructed. Listen for bearing noise during the first hour of operation.
5. Reference / homing: Run the axis homing sequence; confirm the drives accept the enable chain and reach the position setpoints.

9. Related Alarms and Follow-up Checks

Other SINAMICS fan and power-unit service alarms that may appear on the same drive line-up and follow a similar reset logic include:

If 208500 recurs shortly after a reset, the fan-hour counter is being driven by a different DO (e.g. a Motor Module fan, not the ALM). Each DO has its own p0251/p0252. Use the DO index shown in the HMI alarm to target the correct one.

10. Field-Proven Caveats

• E-Stop is the cleanest disable: Some service engineers report success with NCK Reset followed by terminal ES, but on an 840D sl the most reliable way to drop pulse enable on the ALM and all Motor Modules is the hardware Emergency Stop. Drive enable is a hard-wired chain; do not try to fake it with software.
• p0003 sticks per DO: Setting p0003 = 3 on the ALM does not propagate to other DOs. If the alarm actually points to a Motor Module (e.g. Slave003:SVM_00), repeat p0003 = 3 there.
• Slot assignment matters: On PROFINET-based NCU 710.3 PN, the DO-to-slave mapping is defined in the SINUMERIK commissioning archive and in HW Config / TIA Portal topology. If a third-party retrofit changed the topology, the HMI alarm string may show a different slave number than the physical ALM slot - validate against the topology before assuming you are writing to the right drive.
• Parameter write protection bits: Some SINAMICS firmware versions also enforce p0922/p0923 profile-specific write protection. The pulse-inhibit state clears most of these, but a service engineer may still need to enter a manufacturer password at the drive itself, not just at the HMI.
• Counter is non-volatile: p0251 is stored in non-volatile memory on the ALM's EEPROM / flash. A standard NCK Reset will not clear it; the explicit write to zero is required.
• Do not use p0971 to factory-reset to clear this alarm. p0971 / p0976 reset the entire drive to defaults and require re-commissioning of motor data. The correct, safe, scoped remedy is p0251[0] = 0.

11. Quick Diagnostic Flow

Alarm DP003.Slave003:XLM_00 (2) appears
  |
  +--> Replace ALM fan physically
  |
  +--> E-Stop engaged?  --- No --> Press E-Stop, wait for drives to drop
  |         |
  |        Yes
  |         |
  +--> HMI logged in as Manufacturer?  --- No --> Log in, enter password
  |         |
  |        Yes
  |         |
  +--> In infeed screen, p0003 = 3 ?  --- No --> Set p0003 = 3
  |         |
  |        Yes
  |         |
  +--> p0251[0] = 0 write accepted?  --- No --> Re-check r0899.0; wait longer
  |         |
  |        Yes
  |         |
  +--> Release E-Stop, run homing, monitor r0070 DC link

12. References in This Procedure

Use the official Siemens documentation set for verification against your specific firmware version:

• SINAMICS S120/S150 List Manual (parameter list)
• SINAMICS S120 Equipment Manual for Book Size Power Units
• SINUMERIK 840D sl Commissioning Manual (NCU 710.3 PN)
• SINUMERIK 840D sl Operator Components and Service Manuals