Resolving Siemens MM440 F0015 Fault with PTC Sensor

1. F0015 with Valid PTC Resistance: Problem Definition

A Siemens MICROMASTER 440 (MM440) inverter trips F0015 (no motor temperature signal) with a measured PTC resistance of 256 Ω at control terminals 14 and 15, even after pressing the FN (fault acknowledge) key on the Basic Operator Panel (BOP). Standard MM440 trip logic for a PTC sensor on P0601 = 1 expects the following:

• R > 2000 Ω → F0001 (motor overheating)
• 100 Ω ≤ R ≤ 2000 Ω → normal operation, no trip
• R < 100 Ω → F0015 (signal short / wire break)

A 256 Ω reading is well inside the valid PTC band. The F0015 trip under this condition indicates the input is no longer being interpreted as a PTC element, the input conditioning stage has been driven into a non-linear region, or a stale parameter set is forcing the wrong sensor model. The reported r0035 = 20 with a sensor type that should not produce a linear temperature reading is the second diagnostic clue.

2. F0015 Fault Definition and Trip Thresholds

F0015 is grouped in the MM440 fault list under "Motor temperature signal lost." The fault fires whenever P0601 ≠ 0 (a sensor is selected) and the analog front end cannot resolve a valid temperature. The exact trip threshold depends on the sensor model chosen in P0601.

The MM440 evaluates the PTC trip with a small hysteresis band centred on the 100 Ω / 2000 Ω transition. Once a fault has latched, the input is treated as invalid until the next power cycle or successful fault acknowledge through the BOP, the digital input wired to P2103, or a serial/PROFIBUS control word bit (r2090 bit 7). FN on the BOP clears the fault bit but does not change the sensor interpretation.

3. MM440 Temperature Monitoring Architecture

Terminals 14 and 15 are routed through a differential analog front end that feeds an internal voltage-controlled oscillator. The DSP measures the oscillator period and maps it to either:

• A binary PTC state (cold / hot / open / short) when P0601 = 1
• A linear temperature in °C (KTY84 / PT1000 model) when P0601 = 2 or 4

Three parameter groups interact with the result:

The index [0] always refers to motor data set 1 (MDS1) and [1] to MDS2. The active data set is shown in r0050 (bit 0) and can be switched by a digital input wired to P0820/P0821. If only P0601[0] is set to 1 and the drive is running on MDS2 with P0601[1] = 2, the front end will be configured for KTY84 even though the operator believes the drive is in PTC mode. This is the single most common reason for a "valid PTC resistance still trips F0015" field complaint.

4. Terminal 14/15 PTC Wiring Requirements

Wiring constraints that affect a 256 Ω reading:

• Use a twisted, shielded pair. The shield is grounded at the drive end only (PE bar near the control terminals) to avoid ground loops.
• Keep the cable length < 100 m. Each metre of typical 0.75 mm² copper adds ~0.025 Ω, so cable resistance is not the cause of F0015 at 256 Ω.
• Do not run the PTC cable in the same conduit as the motor output cables (U2/V2/W2). Capacitive coupling can offset the analog input.
• Verify that terminal 14 / 15 jumpers to other analog inputs are removed. Some MM440 variants share a ground reference; a stray jumper creates a parallel path that pulls the reading low.

5. r0035 Diagnostic Reading and Interpretation

r0035[0] is the live motor temperature display. Its semantic depends on P0601:

A reading of r0035 = 20 °C with a 256 Ω input therefore points to one of two states:

1. The drive is configured as KTY84 (P0601 = 2) and the input is being interpreted linearly — in which case the F0015 is a sensor-loss fault because the firmware cannot reconcile 256 Ω with a KTY84 cold-start value. A 256 Ω reading in KTY84 mode maps to approximately -10 °C, which is below the legal input range and trips the loss-of-signal path.
2. P0601 is set to PTC (1) but the firmware is reading the value through the KTY84 conversion path due to a parameter-set mismatch (MDS1 vs MDS2).

In both cases, the answer is the same: verify P0601 on the active motor data set, not on the index that the operator remembers editing.

6. Parameter Diagnostic Matrix

Before any reset attempt, capture the live state of every parameter that influences the temperature path. The minimum set on the BOP is:

r0035[0]    ; live motor temperature (°C)
r0035[1]    ; live motor temperature MDS2
r0050       ; active motor data set
P0601[0]    ; sensor type MDS1
P0601[1]    ; sensor type MDS2
P0604       ; threshold (KTY84/PT1000)
P0610[0]    ; I²t reaction MDS1
P0612       ; thermal model
P0625       ; ambient temperature at commissioning
r0947       ; last fault code (should be 15)
r0948       ; fault time (drives clock hours)
r0949       ; fault value (often 0 for F0015)

For the reported field case the values were:

Note the symmetry between r0035 = 20 and P0625 = 20. When the sensor is in an invalid state, the firmware falls back to the P0625 ambient seed for the r0035 display. This is a strong indicator that the analog front end is rejecting the 256 Ω input as out-of-range.

7. Root Cause Analysis: Why F0015 Trips with 256 Ω

Three hypotheses fit the symptoms. Rank by probability and verify in order.

7.1 Sensor type mismatch on the active motor data set

The most common field cause. The operator changes P0601[0] to 1 (PTC) but the drive is running on MDS2 with P0601[1] = 2 (KTY84). The analog front end is then configured for KTY84 linear conversion, the 256 Ω input maps below 0 °C, the firmware declares the signal lost, and F0015 latches. FN clears the latch but the input remains invalid.

7.2 Firmware version and KTY84/PT1000 interpretation

Older MM440 firmware revisions (1.x) interpret a low-resistance input on terminals 14/15 as a short, which is exactly the F0015 trigger for P0601 = 1. Firmware 2.x and later use a more tolerant mapping but the trip path is preserved. A flash upgrade to a current firmware release (see Siemens Industry Online Support for the latest MM440 firmware for the specific frame size) is a known corrective action for false-positive F0015 reports. Refer to the Siemens Industry Online Support knowledge base for firmware download and flashing procedure for MICROMASTER 4 drives.

7.3 Hardware fault on the analog front end

The MM440 control board can develop a leakage path on the 14/15 differential pair after thermal cycling. A reading of 256 Ω at the terminals is correct, but the input stage saturates and the firmware reads an effective short. The fastest check is to swap the control board (CUD) with a known-good unit on an identical frame. If the fault follows the board, replace the CUD. If the fault stays on the drive, re-check P0601, P0610, P0625 and the wiring.

8. FN Reset Procedure and Limitations

The FN key on the BOP triggers fault acknowledgement by setting the corresponding bit in the control word (r2090.7 equivalent for the BOP path). It does the following:

1. Clears the latched fault bit in r0947 (and r2110 history).
2. Releases the OFF1 / OFF3 lockout so the drive can be re-started.
3. Does not re-run the sensor diagnostic. If the analog input is still out of range, the fault re-asserts on the next processing cycle (typically within 20 – 40 ms).

To clear a persistent F0015 properly, work through the following sequence on the BOP:

1. Press FN to acknowledge. Confirm the display returns to the operating screen (e.g. frequency setpoint).
2. Toggle to P0010 = 0 and r0000 = 0 to put the drive in display mode.
3. Cycle parameter index on P0601 by pressing the Fn arrow until the BOP shows P0601[1]. Record both P0601[0] and P0601[1] values.
4. Switch the drive to the motor data set that matches the connected PTC. Use a digital input wired to P0820 = 722.x (DDS/MDS selection) or temporarily force MDS1 with P0820 = 0 and P0821 = 0.
5. Press FN again. If the fault clears for more than 5 s, the cause is MDS mismatch.

If the fault re-asserts immediately, the input is electrically invalid. Proceed to Section 9.

9. Persistent Fault Resolution Path

10. Factory Reset and Re-Commissioning

If the FN acknowledge loop is endless, perform a full parameter reset and re-commission from a known-good baseline.

1. Set P0010 = 30 (factory settings).
2. Set P0970 = 1 and press P on the BOP. The drive resets all parameters to factory defaults and latches a brief "BUSY" message. Wait until the BOP returns to the operating screen.
3. Set P0010 = 0 to leave the reset menu.
4. Re-run quick commissioning: P0010 = 1 (quick commissioning), set motor data in P0300 – P0311, P0335, motor I²t in P0611 / P0612, sensor in P0601, and P0625 to the actual ambient.
5. Exit quick commissioning: P3900 = 1 (full calculation) or P3900 = 3 (calculation only, no I/O reset).
6. Save with P0971 = 1 (save to EEPROM). The save takes 3 – 5 s. Do not power off the drive during this window; an interrupted save can revert the unit to factory defaults on the next power-up, which is a documented field issue on MM440 units with old EEPROM revisions.

11. Verification and Acceptance Test

After the reset, run an acceptance test to confirm F0015 does not return under normal or faulted sensor conditions.

1. Cold sensor: With the PTC at room temperature and connected, confirm r0035[0] = 0 °C (PTC mode) and the drive runs in local mode without tripping.
2. Hot simulation: Replace the PTC with a 4.7 kΩ resistor. The drive must trip F0001 within 200 ms of the next processing cycle.
3. Wire break simulation: Disconnect one wire from terminal 14. The drive must trip F0015. Reconnect the wire and press FN; the drive must restart.
4. Short simulation: Place a 50 Ω resistor across terminals 14/15. The drive must trip F0015. Remove the resistor and press FN.
5. MDS switch test: If MDS2 is used, force MDS1 (P0820 = 0, P0821 = 0) and verify the drive uses the sensor selected in P0601[0].
6. Save and cold restart: Run P0971 = 1, wait 5 s, power-cycle the drive, and confirm the same parameter set is loaded.

Log the following into the commissioning record: r0035, r0050, P0601[0], P0601[1], P0604, P0610, P0625, r0947, and the firmware version (read on the BOP splash screen at power-up, or via r0018 / the parameter dump).

12. Field Notes and Edge Cases

12.1 r0035 echoes P0625 when the sensor is invalid

The MM440 firmware seeds the displayed motor temperature from P0625 whenever the analog input is unreadable. A field case showing r0035 = 20 and P0625 = 20 is a strong indicator that the front end has flagged the input as invalid, which is internally consistent with an F0015 trip even if the resistance is in the PTC valid band.

12.2 KTY84 interpretation of 256 Ω

A KTY84 sensor at 256 Ω maps to approximately -10 °C on the published KTY84 resistance-temperature curve. The MM440 thermal model treats readings below -20 °C as a sensor loss condition. If the drive is accidentally in KTY84 mode with a PTC element on the terminals, the F0015 trip is correct behaviour, not a fault.

12.3 PTC at the cable break threshold

Some MM440 revisions (early 1.x firmware) report F0015 with a 150 Ω – 200 Ω PTC when the cable is > 80 m. The high cable capacitance drags the oscillator period past the F0015 short-circuit threshold even though the DC resistance is in band. Reducing cable length, lowering P0604 = 130 to a larger value (KTY84 only, no effect on PTC) or upgrading firmware are the three corrective paths. None of these are valid options if the cable length is dictated by the installation.

12.4 Simultaneous F0001 and F0015

If the BOP shows F0001 in r0947[0] and F0015 in r0947[1], the sensor is unstable. The first fault is the actual cause; the second is a re-trigger of the same input from a different state. Clear r0947[1] and address the wiring, then re-evaluate. P0952 holds the fault code index for r0947.

12.5 P0610 = 0 disables only the I²t reaction

Setting P0610 = 0 does not disable the sensor path. The drive still monitors P0601, still trips F0001 and F0015, and still writes r0035. If the goal is to silence F0015 without removing the sensor, set P0601 = 0 — but accept that motor thermal protection is gone.

12.6 Frame size and firmware

MM440 covers frame sizes A through F (0.12 kW to 250 kW). Firmware revisions are not always interchangeable across frame sizes. Always flash the firmware variant that matches the MLFB (order number) on the nameplate. The Siemens Industry Online Support entry for MICROMASTER 4 lists the firmware compatibility matrix for each frame size.

13. Quick Reference Card