Replacing 6ES7155-6AA01-0BN0 with 6AA02-0BN0 ET 200SP IM

Overview: Direct Successor Replacement of the IM 155-6 PN ST

The 6ES7155-6AA01-0BN0 and 6ES7155-6AA02-0BN0 are two successive variants of the SIMATIC ET 200SP distributed I/O system interface module, IM 155-6 PN ST. The 6AA02 is a form-fit successor introduced as part of the broader phase-out of the first-generation IM 155-6 PN ST family (6AU01-0BN0 and 6AA01-0BN0). For maintenance engineers who need to swap a failed head module on an existing PROFINET station without modifying the TIA Portal hardware configuration, the 6AA02-0BN0 is the officially documented drop-in replacement.

This article documents:

• The exact compatibility status between 6AA01 and 6AA02 as published by Siemens.
• The diagnostic fault pattern that drives the replacement decision in vibrating installations.
• The hardware swap procedure that preserves the GSDML-based device configuration.
• The strain-relief bracket option (6ES7193-6RA00-1AN0) that mitigates the underlying connector-fatigue failure mode.
• Field-proven verification steps and a fault-code-to-cause matrix.

Compatibility Analysis: 6AA01-0BN0 vs 6AA02-0BN0

According to the Siemens phase-out declaration, the IM 155-6 PN ST variant 6ES7155-6AA01-0BN0 is fully replaced by the successor variant 6ES7155-6AA02-0BN0. The declaration states that the successor can be swapped in without modifying the hardware configuration. Field engineers confirm this is true for the PROFINET device name, device number, IP address, slot assignment, and submodule parameter set, as long as the firmware on the PROFINET controller (S7-1200, S7-1500, ET 200SP CPU, or third-party controller) and the GSDML version in TIA Portal V13+ remain unchanged.

The same device description (GSDML) entry is used by both article numbers, so the IO controller does not see a different device when the head module is physically replaced. This is the technical reason the swap can be performed without changing the hardware configuration in the TIA Portal project, the GSDML installation, or the device-proxy in the controller.

Identifying the Failure Mode: PROFINET Diagnostic Pattern

The diagnostic text that triggers the replacement decision typically appears in the IO controller's online diagnostics as:

Error: I/O device failure - Data transfer fault (no frame received)
Potential inhibit/break reason for next start up:
- unacceptable configuration difference (wrong or missing component)
(I/O profinet name)

This error string contains three pieces of information that point to a cable/connector problem rather than a configuration problem:

1. "Data transfer fault (no frame received)" indicates that the IO controller's PROFINET scanner lost the cyclic frame from the IO device. The IM's PROFINET interface is functional, but the physical link has dropped intermittently.
2. "Unacceptable configuration difference" is the secondary inhibit reason assigned by the controller because, when the device returns, its slot configuration no longer matches the project for that cycle.
3. The I/O PROFINET name in parentheses is the device that dropped. Replacing the IM is only justified when this name points to the same IM that the rest of the station is connected to.

Root Cause: Vibration-Induced PROFINET Faults

The specific use case documented by the source involves a moving I/O cluster subjected to continuous mechanical vibration. The most common failure mechanism in such installations is connector-pin fatigue inside the M12 or RJ45 bus-adapter contact, aggravated by:

• Repeated flexure of PROFINET cable at a radius below the manufacturer's minimum bend radius (typically 4× the cable outer diameter for fixed installation and 8× for continuous flex).
• Axial and transverse load on the bus-adapter connector that the connector's strain-relief geometry was not designed to absorb.
• Loosening of the bus-adapter latch under vibration, producing intermittent contact resistance at the M12 or RJ45 pins.
• Shield-termination loss at the connector backshell when the cable jacket migrates under vibration.

When the contact resistance on any pair of the PROFINET cable rises, the IM's PHY detects CRC errors, link-down events, and ultimately a "no frame received" state that the IO controller reports as a device failure.

Daisy Chain vs Star Topology

The source documents a transition from daisy-chain to star topology using an unmanaged switch. Both topologies are valid for PROFINET, but they have different behaviors under intermittent failure:

The unmanaged switch solution does not eliminate the root cause; it limits the blast radius. The connector-fatigue problem on the moving cable still exists, but only the affected device drops, not the entire station. The strain-relief bracket addresses the root cause.

Hardware Replacement Procedure

Prerequisites

• Replacement IM 6ES7155-6AA02-0BN0 (verified successor, same family letter "A").
• Bus adapter(s) from the failed IM — these are removable and reusable on the new IM (BA 2×RJ45, BA 2×FC, BA 2×SCRJ, or BA SCRJ/RJ45 depending on site cabling).
• Spare BA plug if the old one is damaged.
• TIA Portal project (read-only access is sufficient if GSDML is unchanged).
• ESD-safe workspace and a screwdriver for the spring-loaded terminal release on the BaseUnit type A0.

Step-by-Step Swap

1. Power down the ET 200SP station. The IM is hot-swappable in the sense that the BaseUnit power contacts are isolated when the IM is removed, but the PROFINET cable and the load group on the station should be de-energized to avoid any backplane inrush.
2. Document the PROFINET device name and IP. Read the current assignment from the TIA Portal project (Devices & networks → PROFINET device → Properties → Ethernet addresses). Note: replacing the IM with the same article number does not change the MAC or device name, but write them down as a recovery reference.
3. Remove the PROFINET cable from the bus adapter. Do not pull on the cable; depress the connector latch.
4. Release the IM from the BaseUnit. The IM is held by a single release lever on the front. Lift the lever and pivot the IM out of the BaseUnit.
5. Transfer the bus adapter(s) from the old IM to the new IM. The two BA slots on the IM are labeled X1 (port 1) and X2 (port 2). Match the labels on the cabling so port 1 and port 2 swap consistently.
6. Install the strain-relief bracket 6ES7193-6RA00-1AN0 at the same time, if the new IM supports it (6AA02-0BN0 does). See the bracket section below.
7. Seat the new IM on the BaseUnit. The IM clicks into the BaseUnit when the release lever is in the closed position. Verify that the lever is fully down and that the power and link LEDs illuminate without a steady red.
8. Reconnect the PROFINET cable. Confirm the latch clicks on both sides of the M12 or RJ45 connector.
9. Re-apply power to the station. The IO controller will issue an AR (Application Relationship) request to the device. The PROFINET name is retained; no re-assignment is required.
10. Verify the station in TIA Portal online mode. The IM should be online, the modules in the slot configuration should all be reachable, and the diagnostic buffer should not show new "station failure" entries.

Strain-Relief Bracket Solution: 6ES7193-6RA00-1AN0

The strain-relief bracket is a mechanical accessory that clamps the PROFINET cable to the IM housing, transferring the cable's axial and transverse load from the connector to the bracket. This addresses the connector-fatigue root cause described above.

Earlier IM variants (6AA01-0BN0) have a slightly different housing geometry, and the same 6RA00 bracket may not seat correctly. The 6AA02-0BN0 housing includes the capture features that the 6RA00 bracket is designed for. This is one of the practical reasons a maintenance engineer should consider the 6AA02 swap when installing the strain-relief bracket.

Installation of the Bracket

1. After the IM is seated on the BaseUnit and the PROFINET cable is connected, route the cable through the bracket's cable channel.
2. Seat the bracket on the IM's bracket mount until the snap-fits engage.
3. Tighten the cable clamp screws to the specified torque (typically 0.5 Nm, verify with the bracket's manual).
4. Confirm that pulling on the cable does not transmit force to the M12 or RJ45 connector itself.

Diagnostic Buffer Analysis Procedure

Before replacing the IM, validate that the error pattern is consistent with a cable/connector problem. The TIA Portal diagnostic buffer of the IO controller (or the web server of the IM itself, if accessible) records events with timestamps. Use the following procedure:

1. Open the IO controller online in TIA Portal.
2. Navigate to Online & diagnostics → Diagnostics buffer.
3. Filter for PROFINET IO events.
4. Confirm that the events are clustered around periods of machine motion (e.g., axis travel, robot motion, conveyor start/stop).
5. Look for the entry "I/O device failure - Data transfer fault" followed within a few seconds by "I/O device returns" or "Station failure".

If the entries are clustered around motion events, the failure is mechanical. If they are random or correlated with electrical transients (VFD switching, welding, etc.), the failure is electrical. The replacement strategy differs; for an electrical fault, also inspect the shield bonding and consider a PROFINET cable with reinforced shielding (PROFINET Type C, 4-core, double-shield).

Cable and Connector Best Practices for Vibrating Installations

For installations where cable ties were the only retention method (as documented in the source), the field engineer should re-evaluate the cable specification. A cable rated for fixed installation will fail in continuous flex regardless of how well it is tied.

Verification and Commissioning

1. After the swap and bracket installation, run the machine through a full motion profile.
2. Monitor the diagnostic buffer for at least 30 minutes of typical production cycles.
3. Confirm zero new "I/O device failure" entries.
4. Verify the PROFINET name and IP on the replaced IM via the IO controller's online view.
5. Verify all I/O modules in the station are reachable and the slot configuration matches.
6. Document the new IM's serial number and the strain-relief bracket installation in the asset record.

Troubleshooting Matrix

Additional Engineering Notes

• Field-replaceable parts on the IM: The bus adapter is the only user-replaceable part. The IM's electronics are not field-serviceable; failed units are replaced whole.
• ESD handling: The IM contains ESD-sensitive components. Use a grounded wrist strap and ESD mat during the swap.
• Firmware: The 6AA02-0BN0 ships with the production firmware. Do not attempt to downgrade. The TIA Portal project does not need a firmware update to recognize the new IM if the same GSDML is used.
• Safety integration: If the station is part of a PROFI safe configuration, the swap does not affect the safety slot or the F-host signature. The new IM will inherit the same safety slot assignment automatically.
• Documentation: Record the swap in the plant's PROFINET topology document. The serial number of the head module is the only thing that changes; the device name, IP, and slot configuration are unchanged.