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Knorr-Bremse Group Software Engineer Interview Guide

Knorr-Bremse Group Software Engineer interview guide: reported rounds, questions and how candidates describe the process.

The 60-second brief

As a Software Engineer at Knorr-Bremse Group, you will design and develop safety-critical software that powers the world’s leading braking and control systems for rail and commercial vehicles. Your work directly impacts the safety, efficiency, and reliability of transit networks and freight systems globally. This is not typical application development; you will build software where performance, real-time execution, and absolute reliability are matters of public safety. You will work at the intersection of hardware and software, collaborating closely with mechatronics, electrical, and systems engineers. Depending on your team, you could write low-level firmware for microcontrollers, implement model-based designs in MATLAB and Simulink, or develop control algorithms for complex pneumatic and hydraulic braking systems.

This guide is scoped to a Software Engineer candidate at Knorr-Bremse Group.

Focus areas

  • C
  • Embedded Systems
  • Microcontrollers

The Knorr-Bremse Group interview process

Knorr-Bremse Group candidates report 4 rounds over 3-5 weeks. The stages below are what candidates describe, not a published process.

HR Phone Screening

Initial call to discuss your background, career goals, and basic qualifications.

What to demonstrate

  • Initial call to discuss your background, career goals, and basic qualifications
  • Depth in C

How to prepare

  • Be able to walk your CV end to end in two minutes, and say why this company specifically.
  • Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.

Technical Assessment

Completion of a technical assessment or aptitude test covering logical reasoning and programming concepts.

What to demonstrate

  • Completion of a technical assessment or aptitude test covering logical reasoning and programming concepts
  • Depth in C

How to prepare

  • Answer aloud and timed: Write a C function to reverse a string in place without allocating additional memory.
  • Answer aloud and timed: Explain the difference between call-by-value and call-by-reference. How does this affect memory stack usage in microcontrollers?

Deep-Dive Technical Interviews

Interviews with senior engineers and team leads focusing on domain knowledge and problem-solving skills.

What to demonstrate

  • Interviews with senior engineers and team leads focusing on domain knowledge and problem-solving skills
  • Depth in C

How to prepare

  • Answer aloud and timed: What is a NULL pointer, and how do you prevent dereferencing errors in safety-critical systems?
  • Answer aloud and timed: Explain how you would configure an Analog-to-Digital Converter (ADC) and a timer to measure temperature updates at regular intervals.

Managerial and HR Discussion

Meeting with hiring managers and HR to discuss team integration, working styles, and compensation.

What to demonstrate

  • Meeting with hiring managers and HR to discuss team integration, working styles, and compensation
  • Depth in C

How to prepare

  • Answer aloud and timed: How does the SPI protocol handle multi-slave communication compared to I2C?
  • Answer aloud and timed: Detail the structure of a CAN data frame. How does bus arbitration work in a CAN network?

Where candidates lose points

Brush up on basic electronics

Do not assume you will only be asked software questions. Be ready to explain basic circuit concepts, such as voltage dividers, pull-up resistors, and how analog signals are digitized.

Prepare for pen-and-paper tests

Many global locations utilize written tests during the initial stages. Practice writing clean, syntactically correct C code, solving logical reasoning puzzles, and answering basic engineering questions by hand.

Emphasize safety and quality

Throughout your interviews, highlight your commitment to rigorous testing and code quality. Mentioning experience with static analysis tools, code reviews, or unit testing frameworks will resonate strongly with the panel.

Know your projects inside out

Be prepared to walk through your resume in detail. Your interviewers will ask deep, probing questions about your previous projects, looking to understand your specific contributions, the technical challenges you faced, and how you resolved them.

Questions & practice

What is the difference between a pointer to a constant and a constant pointer? Write the syntax for both in C.

Medium · Embedded C & Pointer Manipulation

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Write a C function to reverse a string in place without allocating additional memory.

Medium · Embedded C & Pointer Manipulation

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Explain the difference between call-by-value and call-by-reference. How does this affect memory stack usage in

Medium · Embedded C & Pointer Manipulation

Explain the difference between call-by-value and call-by-reference. How does this affect memory stack usage in microcontrollers?

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

What is a NULL pointer, and how do you prevent dereferencing errors in safety-critical systems?

Medium · Embedded C & Pointer Manipulation

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

What inputs and boundary conditions would you select to efficiently test a newly designed control block?

Medium · Control Systems & Model-Based Design

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

How do you implement the Singleton design pattern, and what are its thread-safety implications?

Medium · Object-Oriented Programming & Enterprise

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Write the update path that detects a concurrent edit

Medium · optimistic concurrency · transactional outbox · audit history

resource carries version INT NOT NULL DEFAULT 1. resource_revision holds revision_id, resource_id, version, actor_user_id, change_kind, patch JSONB, request_id, created_at with UNIQUE (resource_id, version). outbox_event holds aggregate_type, aggregate_id, aggregate_version, event_type, payload, status. A PUT carries the version the client read. Write the exact statements for the single transaction that applies the edit, records the revision and enqueues 'resource.updated', and give the handler's branch on zero affected rows. Then say what PostgreSQL 16 does under READ COMMITTED when two of these updates hit one row at once.

Approach

  1. One transaction, three writes, no network call inside it: UPDATE resource SET title = $3, version = version + 1, updated_at = now() WHERE resource_id = $1 AND tenant_id = $4 AND version = $2; then INSERT the resource_revision row at version $2 + 1; then INSERT the outbox_event row at the same aggregate_version. The event goes to a table rather than a broker because no transaction spans both.
  2. Branch on the affected-row count before doing anything else. Zero has three causes — stale version, wrong tenant, row gone — so re-read once and map to 409 carrying the current version, or 404 for an id outside the caller's tenant, which also stops the endpoint confirming that another tenant's id exists.
  3. State the engine behaviour instead of assuming it. Under READ COMMITTED the second UPDATE blocks on the row lock, and when the first commits PostgreSQL re-evaluates the WHERE clause against the newly committed row, so the version predicate now fails and the statement reports zero rows. Under REPEATABLE READ the identical collision raises SQLSTATE 40001 instead, so the handler must fold both shapes into one conflict response.
  4. Keep UNIQUE (resource_id, version) even though the predicate already serialises writers. It is what makes a lost update unwritable if any other path ever reaches the revision table, and it converts a logic bug into 23505 rather than into a silently missing history row.

Follow-up

  • A client sends the version it read ten minutes ago and the resource has moved three versions. What is in your 409 so it can resolve the conflict without a full re-fetch?
  • Two editors, two disjoint fields, no overlap. Does your answer still refuse the second write, and should it?

Find version gaps and relay lag with window functions

Medium · window functions · event tables · frame semantics

outbox_event holds event_id, aggregate_type, aggregate_id, aggregate_version, event_type, payload, status ('pending','published','dead'), attempts, created_at, published_at. A projection is missing rows and you must decide whether the relay skipped events or the consumer dropped them. Write three queries over the last seven days: one listing every aggregate_id whose published aggregate_version sequence has a hole, one giving per-day counts with a running total, and one returning the newest published event per aggregate. For each, say where the window function is evaluated relative to WHERE and LIMIT. PostgreSQL 16.

Approach

  1. Gaps: compute lead(aggregate_version) OVER (PARTITION BY aggregate_id ORDER BY aggregate_version) in a subquery, then filter next_version <> aggregate_version + 1 in the outer query. Window functions are evaluated after WHERE, GROUP BY and HAVING and before the outer ORDER BY and LIMIT, so the predicate cannot sit in the same WHERE clause and PostgreSQL 16 has no QUALIFY.
  2. Say what the seven-day filter does to the answer: it truncates every partition, so the first row per aggregate has no predecessor inside the window and a hole spanning the boundary is invisible. Widen the window, or join to resource.version as the authority for the true maximum.
  3. Running total: SELECT date_trunc('day', created_at) AS d, count() AS n, sum(count()) OVER (ORDER BY date_trunc('day', created_at) ROWS UNBOUNDED PRECEDING). An aggregate inside a window call is legal because grouping runs before windowing. The grouping key is unique per row here so ROWS and RANGE agree, but write the frame anyway — over ungrouped rows with tied timestamps the default RANGE frame pulls in every peer row and the total jumps.
  4. Newest per aggregate: DISTINCT ON (aggregate_id) ... ORDER BY aggregate_id, aggregate_version DESC is the cheap PostgreSQL-only form when an index matches that order; row_number() OVER (PARTITION BY aggregate_id ORDER BY aggregate_version DESC) = 1 is the portable form and needs a subquery for the same evaluation-order reason as the gap query.

Follow-up

  • Relay failover redelivers events. Does a duplicate break the gap query, and how would you detect one from this table alone?
  • Turn the gap check into a continuous monitor rather than a query someone runs after an incident. What does it watch?

Explain the practical differences between a structure and a union. When would you use a union in an embedded s

Medium · Embedded C & Pointer Manipulation

Explain the practical differences between a structure and a union. When would you use a union in an embedded system?

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Explain how you would configure an Analog-to-Digital Converter (ADC) and a timer to measure temperature update

Medium · Microcontrollers & Hardware Protocols

Explain how you would configure an Analog-to-Digital Converter (ADC) and a timer to measure temperature updates at regular intervals.

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

How does the SPI protocol handle multi-slave communication compared to I2C?

Medium · Microcontrollers & Hardware Protocols

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Detail the structure of a CAN data frame. How does bus arbitration work in a CAN network?

Medium · Microcontrollers & Hardware Protocols

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

What is a voltage divider network, and how do you calculate the output voltage?

Medium · Microcontrollers & Hardware Protocols

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Explain how 1's complement and 2's complement representations affect arithmetic operations in a microcontrolle

Medium · Microcontrollers & Hardware Protocols

Explain how 1's complement and 2's complement representations affect arithmetic operations in a microcontroller.

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

How do you design and execute a test case in MATLAB and Simulink to validate control logic?

Medium · Control Systems & Model-Based Design

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

Explain how you model real-time physical constraints, such as brake pressure or vehicle deceleration, in a sim

Medium · Control Systems & Model-Based Design

Explain how you model real-time physical constraints, such as brake pressure or vehicle deceleration, in a simulation environment.

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Explain the concept of inheritance with a concrete code example.

Medium · Object-Oriented Programming & Enterprise

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

What is the difference between an abstract class and an interface? When would you choose one over the other?

Medium · Object-Oriented Programming & Enterprise

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Listing latency scales with page size, not with filters

Easy · n+1 · latency · query batching

The tenant listing endpoint reads resource filtered by tenant_id and status, ordered by updated_at DESC, and returns each row plus the owner's display name from app_user and the actor of that resource's latest resource_revision. p99 is 55 ms at 10 rows per page and 1.4 s at 200. Database telemetry shows 401 statements per request, each under 1 ms, and nothing in the slow-query log. Diagnose the cause and give the fix, stating the statement count per request and the p99 you expect afterwards.

Approach

  1. Read the counters before forming a theory. 401 statements for 200 rows is one driver query plus two per row, and sub-millisecond execution with an empty slow-query log rules out a bad plan. The time is round trips, which is why it is invisible in every per-query metric and scales with rows returned rather than with filter selectivity.
  2. Name the two per-row statements from their normalised text: a single-row app_user lookup by user_id, and a resource_revision lookup by resource_id ordered by version DESC LIMIT 1. Confirm by dropping those two response fields and watching the statement count fall to one. That locates the calls in the serialisation layer, not the repository.
  3. Check that the arithmetic accounts for the whole gap. Measure one round trip to the replica in isolation; 400 trips at roughly 3 ms of network plus 0.2 ms of execution is about 1.3 s on top of a 55 ms baseline, which matches. If the multiplication had fallen short, the N+1 would only be part of the story and you would keep looking.
  4. Batch both lookups. Collect owner_user_ids and resource_ids from the driver query, then issue WHERE tenant_id = $1 AND user_id = ANY($2) for the users, and PostgreSQL's SELECT DISTINCT ON (resource_id) ... WHERE resource_id = ANY($2) ORDER BY resource_id, version DESC for the latest revision, which the UNIQUE (resource_id, version) index serves directly. On an engine without DISTINCT ON, use a lateral join or a row_number window. Three statements per request at any page size.

Follow-up

  • The page size is capped at 200 today. What breaks first if it is raised to 2,000, and is it still this bug?
  • How do you stop the next N+1 from reaching production, given that no individual query is slow and the endpoint's tests pass?

Suggested practice checklist

Built from the rounds and topics Knorr-Bremse Group candidates report.

Day 1 — Map the Knorr-Bremse Group loop

  • Write out the reported sequence: HR Phone Screening, Technical Assessment, Deep-Dive Technical Interviews, Managerial and HR Discussion.
  • For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 4 reported rounds, with the weakest marked.

Day 2 — Work C

  • Spend the session on C, which Knorr-Bremse Group candidates report being tested on.
  • Write one worked example in C and time yourself on it.

Deliverable: One timed worked example in C.

Day 3 — Work Embedded Systems

  • Spend the session on Embedded Systems, which Knorr-Bremse Group candidates report being tested on.
  • Write one worked example in Embedded Systems and time yourself on it.

Deliverable: One timed worked example in Embedded Systems.

Day 4 — Work Microcontrollers

  • Spend the session on Microcontrollers, which Knorr-Bremse Group candidates report being tested on.
  • Write one worked example in Microcontrollers and time yourself on it.

Deliverable: One timed worked example in Microcontrollers.

Day 5 — Answer out loud: Embedded C & Pointer Manipulation

  • Answer aloud, timed: What is the difference between a pointer to a constant and a constant pointer? Write the syntax for both in C.
  • Answer aloud, timed: Explain the practical differences between a structure and a union. When would you use a union in an embedded system?

Deliverable: Spoken answers to 2 reported Embedded C & Pointer Manipulation question(s), under time.

Day 6 — Answer out loud: Microcontrollers & Hardware Protocols

  • Answer aloud, timed: Explain how you would configure an Analog-to-Digital Converter (ADC) and a timer to measure temperature updates at regular intervals.
  • Answer aloud, timed: How does the SPI protocol handle multi-slave communication compared to I2C?

Deliverable: Spoken answers to 2 reported Microcontrollers & Hardware Protocols question(s), under time.

Day 7 — Answer out loud: Control Systems & Model-Based Design

  • Answer aloud, timed: How do you design and execute a test case in MATLAB and Simulink to validate control logic?
  • Answer aloud, timed: What inputs and boundary conditions would you select to efficiently test a newly designed control block?

Deliverable: Spoken answers to 2 reported Control Systems & Model-Based Design question(s), under time.

Behavioural preparation

Behavioural rounds judge the decision you made and what it cost.

Describe your experience with Spring Boot or.NET frameworks in building diagnostic tools.

Medium · Object-Oriented Programming & Enterprise

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Describe a time when you had to work on a project or technology stack you did not particularly enjoy. How did

Medium · Behavioral & Situational

Describe a time when you had to work on a project or technology stack you did not particularly enjoy. How did you maintain your quality of work?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

How do you handle high-pressure situations or tight deadlines when a critical software bug is discovered late

Medium · Behavioral & Situational

How do you handle high-pressure situations or tight deadlines when a critical software bug is discovered late in the cycle?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Tell me about a time you had to collaborate with a cross-functional team (such as hardware or quality assuranc

Medium · Behavioral & Situational

Tell me about a time you had to collaborate with a cross-functional team (such as hardware or quality assurance) to resolve a complex system issue.

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?