Resolving SINAMICS S120 Speed Controller Inhibited OFF1 Fault

Problem Definition

When commissioning a SINAMICS S120 multi-axis drive system with the Starter or Startdrive commissioning tool, an asymmetric configuration state can develop between drives that are otherwise identical at the topology level. A common symptom is one axis returning to operation normally after automatic configuration while a second axis reports the simultaneous conditions Speed controller inhibited and OFF1 enable missing in the diagnostic buffer and online status panel. The drive continues to acknowledge parameter writes, but several expert-list parameters that are normally populated by the auto-configuration routine remain at zero. Manual attempts to exit commissioning by writing p10 = 0 are rejected with the diagnostic message Value rejected, and a request to end quick commissioning via p3900 = 3 reverts to p3900 = 0 after a few seconds. Together, these behaviors indicate that the automatic commissioning sequence never reached the calculation phase on the affected drive, leaving the drive object in a half-configured state.

Affected Hardware Topology

The reported configuration consists of a SINAMICS S120 booksize line-up controlled by a CU320-2 PN control unit. The infeed is a Smart Line Module and the two motor axes are served by a Double Motor Module. Both motors come from the 1FK7 synchronous servo family. Identifying the DRIVE-CLiQ capability of each component is the foundation of the root-cause analysis.

The article-number suffix in the 1FK7 family encodes the integrated electronics options. The letter in the 11th position is the deciding field for DRIVE-CLiQ:

• 1FK7022-5AK71-1AG0 – 11th character A: no DRIVE-CLiQ interface; resolver / incremental feedback only, terminal box connection.
• 1FK7022-5AK71-1LG0 – 11th character L: with DRIVE-CLiQ; encoder and electronic nameplate are transferred over the digital interface.

This is the central distinction in the failure scenario. The "L" variant carries an electronic nameplate that the auto-configuration routine reads to populate motor and encoder parameters. The "A" variant carries no electronic nameplate; the auto-configuration routine finds no DRIVE-CLiQ node on that axis and skips parameter population. To complete the topology, an external Sensor Module Cabinet-Mounted (SMC20 for resolvers, SMC30 for incremental encoders such as the IC2048S/R) must be wired into the DRIVE-CLiQ ring of the CU320-2 PN.

Root Cause: Non-DQ Motor Configuration Gap

Auto-configuration in SINAMICS Starter / Startdrive depends on the topology it can read. When Starter performs automatic configuration (drive object creation based on the DRIVE-CLiQ topology), it walks the DRIVE-CLiQ ring and discovers Line Modules, Motor Modules, motors with electronic nameplates, and Sensor Modules. A motor without an integrated DRIVE-CLiQ interface and without an external SMC module wired into the topology is invisible to the auto-configuration routine. The Motor Module creates a drive object, but the motor code, motor equivalent-circuit parameters, and encoder parameters remain at zero.

Consequences on the affected axis:

1. p10 cannot be set to 0. The drive object has not finished the parameter consistency check required to leave commissioning state. Writing p10 = 0 is rejected with "Value rejected" because motor data (p0300 family), encoder data (p0400 family), and the closed-loop control structure reference (p1300) are inconsistent or zero.
2. p3900 = 3 reverts to 0. The end-of-quick-commissioning sequence needs a valid p0300 (motor code selection) and a consistent motor data set. With p0300 = 0 the calculation routine has nothing to compute, the command is accepted briefly, the calculation aborts, and p3900 is written back to 0 by the firmware within a few seconds.
3. "OFF1 enable missing" and "speed controller inhibited" persist. These are status bits driven by the enable logic. The drive stays in state S1 (Ready for switching on) or S2.1 (Ready for operation with controller inhibit) because the missing motor identification means the closed-loop controller cannot be released; the OFF1 signal cannot latch without a configured power unit and motor model.

In short, the automatic configuration successfully wrote a topology into the project for the DQ motor, then encountered the non-DQ motor whose nameplate data could not be read and silently left the drive object incomplete. The user-visible symptom is asymmetric between two otherwise mechanically identical axes.

Diagnostic Procedure and Parameter State Inspection

Before changing any project data, perform the following read-only checks in Starter or Startdrive to confirm the hypothesis.

Read the enable status word

Open the affected drive's Diagnostics > Status / Control panel or read the following parameters online:

• r0046 – Missing enables (bit field). On a faulted axis, bit 0 (OFF1 enable) and bit 21 (speed controller inhibited) are typically set to 1.
• r0047 – Drive status word 1 (state machine S0 / S1 / S2 ...).
• r0052 – Status word 2 (bit 4 = speed controller active).
• r0002 – Current drive state (numeric code from the state machine).

Compare parameter populations between drives

Open the expert list for both drives and look at the parameter groups below. On a successfully auto-configured DQ axis the parameters are populated; on the failing non-DQ axis they are zero.

If the working axis shows e.g. p0300 = 203 (1FK7 DQ family) or p0300 = 207 (third-party synchronous) and the failing axis shows p0300 = 0, the missing parameter set is the smoking gun. The same check on p0400 confirms the encoder side.

Read the drive state and control word

Read r0002 (drive state) and r0898 (control word 1, BICO view). The failing axis will be in S1 (Ready for switching on) rather than S4 (Operation) because no OFF1 has latched. Confirm also that r0050 (active command data set CDS) is 0 or 1 as expected; some multi-axis projects use two CDS to switch motor data between gear stages, and the active CDS can mask which parameter set is actually loaded.

Key Parameter Reference

The following parameters form the minimum surface area that must be valid before the drive can leave commissioning state. They are read from the SINAMICS S120 List Manual.

Resolution Procedure: Manual Offline Commissioning

The successful resolution on a non-DQ axis is to upload the existing drive data into the project, take the project offline, and re-enter the configuration deliberately in the project's configuration tab for that drive object. Auto-configuration is then effectively replaced by manual configuration for that axis.

Prerequisites

• Starter or Startdrive with the project that matches the CU320-2 PN.
• Online connection (PROFINET or PROFIBUS) to the CU320-2 PN.
• Article numbers of the motor, encoder, Sensor Module (if used), and Motor Module.
• Motor data sheet (resistance, inductance, EMF constant, rated current, rated torque).

Step-by-step procedure

1. Upload drive data to the project. Right-click the CU320-2 PN in the project tree and choose Target device > Upload device to PG/PC. The existing on-line configuration is mirrored into the offline project. This step ensures the project reflects what the drive actually has, including the parameters that auto-configuration set to zero.
2. Go offline. Right-click the CU320-2 PN and select Go offline. All further edits must happen offline so the configuration can be compiled and downloaded as a complete package.
3. Open the configuration of the affected SERVO drive object. In the project tree, double-click SERVO_03 (or whatever index the affected axis has). Select the Configuration tab.
4. Configure the power unit. Confirm the Motor Module selection matches the installed hardware (e.g., 6SL3120-2TE13-0AA4). An incorrect power-unit selection changes the current limit, DC link voltage scaling, and overload capability and re-triggers the commissioning filter.
5. Select the motor. In the motor configuration, open the motor catalog. For a 1FK7022-5AK71-1AG0 (non-DQ), the catalog entry is the same motor family but the DRIVE-CLiQ column must be set to "without DQ" or the article number must be entered with the "A" suffix explicitly. If the entry is not in the catalog, switch to Third-party motor or Motor with DRIVE-CLiQ → data entered manually and populate p0300, p0301, p0304, p0305, p0307, p0310, p0311, p0314 from the motor data sheet.
6. Select the encoder. The IC2048S/R L22 incremental encoder is not a DRIVE-CLiQ encoder. Select the SMC channel that the encoder is wired into. For a resolver, configure SMC20 (p0400 in the 1002-1011 series); for an incremental encoder such as the IC2048S/R, configure SMC30 (p0400 in the 3001-3011 series). Set the resolution to 2048 S/R, set inversion (p0410) if the rotation direction is reversed, and set p0421 if the encoder has a commutation track.
7. Set the control mode. Select Speed control with encoder (p1300 = 21) for the affected axis. Encoderless operation is not appropriate here because the IC2048S/R is the position feedback and the motor identification sequence requires it.
8. Save and recompile the project. Press Save and compile. Any inconsistency in the configuration (e.g., a missing motor code for the selected control mode) appears as a compile error and prevents the download.
9. Download to the target. Right-click the CU320-2 PN and select Download to target device. Confirm that the drive object SERVO_03 is included in the download. The download writes the configured motor and encoder data into the affected drive object.
10. End quick commissioning. On the affected drive, set p3900 = 3 (calculate motor equivalent circuit, accept, factory reset I/O). The parameter should return to 0 after a few seconds. If it does not, the motor code is still inconsistent – re-check p0300 and the encoder configuration.
11. Set p10 = 0. The drive should now accept the write and leave commissioning state.
12. Save to ROM. Issue p0977 = 1 to copy the parameter set from RAM to ROM so the values persist across a power cycle.
13. Run motor identification (strongly recommended). For a non-DQ motor that was not identified by auto-configuration, run p1910 = 1 (static motor identification) followed by p1960 = 1 (speed controller optimization). These routines measure the stator resistance, leakage inductance, and main inductance, then run a speed-controller optimization travel profile. Allow the motor shaft to rotate freely during p1960.

Validation checkpoints

• After step 9, the affected drive's r0046 should show all enable bits cleared (OFF1, OFF2, OFF3, inverter enable).
• After step 10, p0300 and p0400 should be non-zero and reflect the configured motor / encoder.
• After step 13, r0052 bit 4 (speed controller active) should set to 1 once a motion command is issued.

Verification and Status Bit Checks

Once the project is downloaded, verify that the affected axis behaves identically to the working axis. Use the Starter control panel or Startdrive trace to check the items in the table below.

Run the drive through a small jogging profile in the control panel (e.g., 100 rpm for 2 s, then -100 rpm for 2 s). Capture r0021 (actual speed smoothed), r0062 (speed setpoint filtered), and r0079 (torque setpoint). On a properly configured axis, all three signals track within the controller bandwidth (default p1460 ≈ 0.7 Nm·s/rad, p1472 ≈ 20 ms after p1960 optimization). Persistent oscillation or torque saturation indicates that the motor identification must be re-run.

Supplementary Troubleshooting Matrix

The "Speed controller inhibited" / "OFF1 enable missing" pair can have causes beyond the auto-configuration gap. The matrix below maps the most common variants to the underlying cause and the appropriate action.

Related SINAMICS faults

Preventive Configuration Best Practices

To avoid this asymmetry on multi-axis projects with mixed DQ / non-DQ motors:

1. Document the DRIVE-CLiQ topology before commissioning. List each axis's motor article number with the 11th character identified. Label every DQ cable, every SMC, and every resolver cable. The article-number-vs-capability table above should be printed and stored with the project.
2. Insert SMC modules into the topology before auto-configuration. If a non-DQ motor is intended, the SMC20 or SMC30 must be physically wired and visible to the CU320-2 PN's DRIVE-CLiQ ring before Starter auto-configuration runs. Auto-configuration will then create the encoder DO and accept the encoder topology.
3. Use manual configuration for mixed axes. In the project's drive configuration, mark DQ axes for auto-configuration and non-DQ axes for manual configuration. This is a project-level decision, not a drive-level one – the configuration tab of each drive object controls it.
4. After every auto-configuration, verify p10 and p3900. Add a commissioning checklist step that reads p10 = 0 and p3900 = 0 on every axis. If either drive reports otherwise, the commissioning is incomplete.
5. Run the motor identification sequence. For every non-DQ axis, run p1910 = 1 (static motor data identification) and p1960 = 1 (speed controller optimization) once the project is downloaded. These routines populate p0350 / p0352 / p0354 / p0356 with measured values and tune p1460 / p1472.
6. Save the project to ROM. After successful commissioning, copy RAM to ROM (p0977 = 1) on each drive object so the parameters survive a power cycle.
7. Use telegram 1/2/3/5 for PLC-driven axes. Standard telegrams pre-wire the control and status word bits; custom telegrams introduce BICO sources that must be reviewed for OFF1 / OFF2 / OFF3 / inverter enable.
8. Check F-CPU and STO wiring. Safety-integrated applications route STO through the F-CPU and the EP terminal strip on the Motor Module. Missing STO ack is one of the most common reasons r0046.1 (OFF2) sets after a mechanical intervention.

Reference documents

• SINAMICS S120 Commissioning Manual – covers auto-configuration, manual configuration, and motor identification.
• SINAMICS S120 List Manual – canonical parameter reference for p0010, p0300, p0400, p3900, r0046, and the rest of the commissioning parameter set.
• SINAMICS S120 Function Manual "Drive Functions" – state machine, OFF1 / OFF2 / OFF3 logic, enable signal sources.
• 1FK7 Synchronous Servo Motors Configuration Manual – motor article number convention and DRIVE-CLiQ variants.
• SINAMICS S120 Control Unit CU320-2 PN Manual – DRIVE-CLiQ topology rules and PROFINET coupling.

Frequently Asked Questions