Siemens Desigo PXC Controller Fault Codes and Resolution

Overview

Siemens PXC controllers (PXC001, PXC36, PXC100) serve as the backbone of Desigo integrated building management systems. This guide covers LED diagnostic patterns, BACnet/ABT communication faults, firmware compatibility issues, point engineering errors, and I/O module failures. The PXC series uses a unique tri-state LED system and maintains detailed fault registers accessible via Desigo CC engineering software. Understanding these fault codes and LED patterns enables rapid diagnosis of controller hardware and software issues.

PXC Controller LED Diagnostic Reference

The PXC series features three status LEDs on the front panel. Unlike simple green/red systems, PXC LEDs use specific blink patterns and combinations to indicate detailed controller state.

LED	Normal State	Meaning	Fault Indication
RUN	Solid Green	Controller executing program and in normal operation	Blinking Green = Controller booting; Off = Power issue or watchdog fault
ERR	Off	No errors detected	Solid Red = Critical fault (controller halted); Blinking Red = Warning/non-critical fault
BUS (ABT)	Solid Green	ABT communication healthy, syncing with engineering station	Blinking Green = Attempting to sync; Red = Communication timeout with Desigo CC

LED Combination Decoder

RUN	ERR	BUS	Diagnosis	Action
Solid Green	Off	Solid Green	Normal operation, no issues	Continue monitoring
Blinking Green	Off	Solid Green	Boot sequence in progress	Wait 2-3 minutes; if persists, check SD card
Off	Solid Red	Off	Power failure or critical fault	Check 24VAC supply; review fault registers
Solid Green	Blinking Red	Solid Green	Non-critical warning active	Check Event Log in Desigo CC; fault is not safety-critical
Solid Green	Off	Blinking Green	Attempting ABT sync with engineering station	Verify network connection; may resolve automatically
Solid Green	Off	Red	ABT communication lost	Check Ethernet cable; verify Desigo CC server is reachable

PXC Fault Code Registry

PXC controllers store fault codes in dedicated fault registers accessible via Desigo CC. Fault codes range from 0x0000 to 0xFFFF and correspond to specific hardware or software conditions.

Critical Faults (RUN LED Off, ERR LED Red)

Fault Code	Fault Name	Root Cause	Resolution
0x0001	Power Supply Failure	24VDC supply voltage out of tolerance (below 19V or above 29V)	Measure voltage at terminal block; check transformer output; verify no short circuits in wiring; replace PSU if voltage erratic
0x0002	Memory Test Failed	DRAM or FLASH memory failed self-test during boot	Attempt cold reboot (remove power 60 seconds); if fault code persists, controller memory is damaged—replace controller
0x0003	Real-Time Clock Battery Low	RTC battery (typically 3V lithium) voltage below 2.5V	Replace RTC battery on main PCB; if unavailable, set time manually after power restore
0x0004	Watchdog Timeout	Firmware hung or infinite loop detected by watchdog timer	Check Desigo CC for program errors; review recent configuration changes; perform factory reset if necessary
0x0005	Configuration Checksum Error	Stored configuration corrupted or incomplete download	Re-download configuration from Desigo CC to controller; use "Verify and Repair" function in CC if available

Communication and BACnet Faults (ERR LED Blinking Red)

Fault Code	Fault Name	Root Cause	Resolution
0x1001	BACnet Stack Initialization Failed	Ethernet driver not responding or hardware missing	Check Ethernet connector; reseat cable; verify network card LEDs illuminate when cable connected
0x1002	BACnet Device ID Conflict	Two or more PXC controllers on network with identical BACnet Device ID	Use Desigo CC network scanner; identify duplicate IDs; reconfigure one controller with unique ID (typically 1-65535)
0x1010	ABT Synchronization Timeout	PXC unable to establish ABT communication with Desigo CC server within 30 seconds	Verify Desigo CC server is running and reachable on network; check firewall for port 10001 (ABT protocol); reboot networking components
0x1011	BACnet Foreign Device Registration Failed	Controller attempted BBMD registration but BBMD unreachable	Verify BBMD IP address in PXC network settings; test connectivity to BBMD; ensure UDP port 47808 is open on firewall
0x1020	Network Interface Down	Ethernet driver detected physical disconnection	Reseat Ethernet cable; test with known-good cable; check network switch port for activity light
0x1030	IP Address Configuration Invalid	Static IP conflicts with existing device or DHCP pool exhausted	Use Desigo CC to change controller IP to unique address; verify no duplicate MAC addresses on network

Module and I/O Faults (Non-Critical, ERR Blinking Red)

Fault Code	Fault Name	Root Cause	Resolution
0x2001	TXM Module Not Detected	TXM expansion module not responding on RS-485 or physically disconnected	Verify TXM module is seated correctly in expansion slot; check termination resistors (120Ω should be present at end of bus); replace TXM if damaged
0x2002	TXM Module Address Conflict	Multiple TXM modules configured with same address	Use Desigo CC to verify each TXM has unique address (typically 1-4); reconfigure duplicate addresses
0x2010	I/O Point Initialization Error (Channel: XX)	I/O module failed to initialize specific channel (analog or digital)	Cycle controller power; if persistent, check analog input wiring; verify 4-20mA loop for analog modules
0x2011	Digital Output Overload	Digital output channel detected excessive current draw (short circuit)	Disconnect load from affected output; measure resistance at load terminals; if shorted, replace load or verify wiring integrity
0x2020	Analog Input Out of Range	Analog input signal missing or outside valid range (typically 0-10V or 4-20mA)	Check sensor wiring and connections; verify sensor power supply; test with known-good sensor if issue persists

Engineering and Configuration Faults

Fault Code	Fault Name	Root Cause	Resolution
0x3001	Engineering Value Out of Range	Calculated point value exceeds configured min/max limits	Open Desigo CC, navigate to point properties, adjust engineering limits to accommodate sensor range; verify sensor calibration
0x3002	Circular Logic Detected	Program or database contains circular reference (e.g., Output A depends on Output A)	Review program logic in Desigo CC; identify circular dependency; restructure logic to break loop
0x3010	Database Corruption Detected	Configuration database has invalid structure or checksum mismatch	Perform factory reset and re-download clean configuration from backup; if no backup available, rebuild configuration manually
0x3011	Insufficient Memory for Points	Point database exceeds available controller memory (PXC001: 500 pts, PXC36: 2000 pts, PXC100: 4000 pts)	Count total points in Desigo CC; remove unused points; consolidate redundant logic; upgrade to larger PXC model if necessary
0x3020	Program Syntax Error	Downloaded program contains invalid syntax or unsupported functions	Review Desigo CC compiler output for specific line and error; correct syntax; re-download program

Common Desigo CC Error Messages

Beyond fault codes stored in the controller, Desigo CC engineering software reports application-level errors visible in the CC interface.

Network and Device Discovery Errors

"Device not found at address XX.XX.XX.XX"

• Symptom: CC cannot reach controller on network
• Cause: Controller offline, wrong IP, network isolation, or firewall blocking
• Fix: Ping IP from workstation; verify IP is correct; check network connectivity; temporarily disable firewall for testing

"ABT Communication Timeout with Device XX"

• Symptom: CC connected at some point but now showing timeout
• Cause: Network outage, firewall rule change, or controller reboot during communication
• Fix: Check network connectivity; wait for controller boot (2-3 minutes); verify firewall allows port 10001 TCP

"Unable to Download Configuration to Device"

• Symptom: CC reports download failed after initiating transfer
• Cause: Network disconnection mid-transfer, controller memory full, or firmware mismatch
• Fix: Verify network is stable; clear some controller memory if possible; confirm firmware version compatibility; retry download

Point and Logic Errors

"Engineering Value Out of Range (Point: HVAC.Temp1)"

• Symptom: Point shows invalid engineering value or CC highlights point in red
• Cause: Sensor reading outside configured min/max limits
• Fix: Check sensor wiring and operation; recalibrate sensor if drift detected; expand engineering limits if sensor is correct

"Duplicate Object ID Detected (OID: 45012)"

• Symptom: CC reports duplicate BACnet object ID during download
• Cause: Two or more points configured with same ID
• Fix: Open point list in CC; search for OID 45012; rename conflicting points to unique IDs

"Invalid Function Block Connection"

• Symptom: CC shows connection error between function blocks in program
• Cause: Output of block A connected to incompatible input type of block B
• Fix: Check data type of source and destination; use converter block if types don't match; review block documentation

Firmware and System Errors

"Firmware Version Mismatch: Controller 3.1.5, Configuration Requires 3.5.0"

• Symptom: Configuration refuses to download; firmware version incompatibility
• Cause: Configuration created in newer firmware version than controller has installed
• Fix: Update controller firmware to match or newer; or downgrade configuration in CC if firmware update unavailable; contact Siemens support for firmware download

"Insufficient Flash Memory for Configuration Download"

• Symptom: Download fails partway through; no space left message
• Cause: Configuration file too large for available controller flash
• Fix: Remove unused points, programs, or trends; split across multiple controllers if necessary; verify no corrupted data blocks on flash

I/O Module Troubleshooting

TXM Module Communication

The TXM expansion modules communicate via RS-485 bus on dedicated connector. Multiple TXM modules can daisy-chain for expanded I/O.

TXM Not Responding:

1. Verify TXM module is firmly seated in expansion slot
2. Check that termination resistor (120Ω) is installed at end of chain
3. Measure RS-485 voltage between + and - terminals (should be approximately 5V in idle state)
4. Use a multimeter in resistance mode to verify terminator is present (should show ~120Ω between + and -)
5. If multiple TXMs, remove each from chain one at a time to isolate faulty module
6. Replace TXM if fault code persists after verification steps

Analog Input Calibration

If analog inputs report incorrect values despite proper wiring:

1. Access calibration menu in Desigo CC: PXC Properties → Calibration
2. Apply known reference signal (e.g., 10V for 0-10V input) to analog input channel
3. Record reading shown by controller
4. Adjust offset/gain values to match known signal
5. Test across range (0%, 50%, 100%) to verify linearity

Desigo CC Configuration Best Practices

Before Downloading Configuration:

1. Always save current controller configuration as backup: File → Export Configuration
2. Verify BACnet Device ID is unique on network
3. Check that all mandatory parameters are filled (Network settings, Device name, etc.)
4. Review any compiler warnings or errors (yellow or red indicators)
5. Confirm controller firmware version matches configuration requirements

After Successful Download:

1. Verify PXC boots normally (RUN solid green, ERR off, BUS solid green)
2. Connect to PXC in Desigo CC; select "Verify Device" to confirm all points present
3. Test a few critical points by toggling outputs or monitoring inputs
4. Save configuration to secure location as backup

General Troubleshooting Tips

Power Supply Issues: Measure voltage at controller terminal block with multimeter. If erratic or low (<19V), check transformer secondary; verify no load is drawing excessive current (check for short circuits in wiring).

Intermittent Network Faults: If BUS LED flickers or ABT sync is slow, check network cable for damage or poor connection. Swap with known-good patch cable to rule out cable issue. If wired into structured cabling, test with temporary cable to bypass wall jack.

Configuration Instability: If controller spontaneously reboots or fault codes appear randomly, suspect corrupted configuration database. Perform factory reset, restore clean backup, or rebuild configuration from scratch.

Module Expansion Planning: Each TXM module adds approximately 16 I/O points. Don't exceed 4 TXM modules per controller due to RS-485 bus limitations. If I/O count exceeds capacity, add additional PXC controllers.

Firmware Maintenance: Document current firmware version before performing updates. Store firmware files and their release notes. Test major firmware updates on non-critical building first.

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Last updated: February 2026. Based on Siemens Desigo PXC firmware versions 3.0 through 3.7 and Desigo CC 6.8+