Siemens S7-300 PLC Replacement Guide: Discontinuation, CPU Options & Cross-Reference (2026)

Siemens S7-300 replacement guide: discontinuation, CPU options & cross-reference (2026)

The SIMATIC S7-300 was Siemens' workhorse mid-range PLC for two decades. Today it is in phased discontinuation: new CPUs, signal modules and interface units are scarce from distributors, and many plants are weighing a like-for-like spare against a full S7-1500 migration. This guide covers what "discontinued" means for the S7-300, the realistic replacement paths when a CPU or module fails, and a cross-reference of common ordering numbers.

Is the S7-300 really discontinued?

For sourcing purposes, yes. Siemens has wound down the S7-300 range and positions the SIMATIC S7-1500 as the successor. That means:

• New S7-300 CPUs and many SM (signal) modules are no longer routinely stocked by Siemens distributors.
• Remaining availability is in new-original surplus / NOS held by independent specialists.
• New projects should target S7-1500; existing S7-300 lines need a sourcing-and-migration plan.

Three paths when an S7-300 CPU or module fails

1. Source new-original stock (fastest recovery)

A like-for-like replacement keeps your existing rack, program and I/O untouched — usually the lowest-risk first move for a critical line. Send us the order number and we'll check current new-original availability.

2. Migrate to S7-1500 (future-proof)

The S7-1500 is a different architecture (TIA Portal, different modules, PROFINET-native). Migration is an engineering project: program conversion, HMI/network rework and re-validation. Right for lines you'll keep for a decade.

3. Substitute within the S7-300 family

A higher-tier CPU of the same interface type can often stand in for a failed lower-tier unit (e.g. a 314 for a 313, where memory and interfaces match). Verify firmware and memory first.

Common S7-300 ordering numbers (cross-reference)

Confirm the exact suffix and firmware generation against the Siemens datasheet — ordering-number details change across firmware revisions.

What to verify before buying a replacement

• Order number & firmware — must match your existing project where required.
• Working memory — the replacement CPU must be ≥ your program size.
• Interface modules — MPI / PROFIBUS DP presence must match your network.
• Rack & PSU — confirm the module seats in your existing rack and the power supply covers it.
• Condition & traceability — insist on new-original with serial-number traceability.

Where to source new-original discontinued S7-300 stock

SHLY-PLC stocks 100% new original, never refurbished Siemens discontinued automation parts, each inspected before dispatch and covered by our 12-month seller warranty. Browse the Siemens collection or the discontinued-products collection, or send the exact order number. See our quality-assurance page for inspection details. For the higher-end line, also see our S7-400 replacement guide, and our FAQ & glossary for terminology.

Frequently asked questions

Can I drop an S7-1500 CPU into an S7-300 rack?
No. Different hardware, engineering tool (TIA Portal vs STEP 7) and modules. An S7-1500 replacement is a migration project, not a swap. Source an S7-300 equivalent first for fast recovery.

How do I read an S7-300 order number?
6ES7 (S7-300 prefix) · 31x = CPU / 32x = signal module · feature codes · 0AB0 (hardware version). Once parsed, matching a replacement becomes straightforward.

Do you sell refurbished S7-300 parts?
No. SHLY-PLC sells only new-original surplus and unused stock — see our stance on why we don't refurbish.