Title: Dependent Failure Analysis in ISO 26262: Beyond Redundancy URL: https://iso26262.academy/blog/practical-tips-for-mastering-dependent-failure-analysis-in-iso-26262 Description: Two channels can share one vulnerability. Explore three ISO 26262 DFA checks for common causes, hidden dependencies and evidence of sufficient independence. --- # Dependent Failure Analysis: Three Checks Beyond Redundancy ![Abstract geometric network of connected nodes against a pale blue background.](https://iso26262.academy/edge-media/p/blog/images/2026/09/58953e56-2c83-4359-ab7f-b917bd73e6ee-1920.webp) Two channels can still share one vulnerability. Learn three practical DFA checks for examining common causes, hidden dependencies and the evidence behind independence claims. ![ISO 26262 Academy](https://iso26262.academy/logo.png) ISO 26262 Academy By [Paul Danci](https://iso26262.academy/about) 29 September 2026 3 min read Share Text size Two controllers. Two signal paths. One shared supply. An architecture can look redundant while still depending on a single vulnerable resource. **Dependent Failure Analysis (DFA) tests the independence assumptions behind a safety concept.** It examines whether a shared cause or failure propagation could defeat the protection the design relies on. ISO 26262-9:2018, Clause 7 addresses this analysis. Here are three practical starting points. ## 1. Follow the cause, not just the timing A **common cause failure** occurs when one event or root cause directly affects multiple elements. A **cascading failure** occurs when one element’s failure causes another to fail. Similar timing alone does not tell you which relationship exists. ![Common cause: one event directly affects A and B. Cascading: failure of A propagates to B.](https://iso26262.academy/edge-media/p/blog/diagrams/2026/09/fed55540-273c-4adb-85df-04bfab4e7d13.svg) Figure 1. Classify the causal relationship, not just when failures appear. For example, an electromagnetic disturbance could upset two controllers directly. Alternatively, one faulty sender could transmit erroneous data that makes another function fail. These are hypothetical examples; the classification depends on the elements and boundaries being analysed. The distinction matters when choosing measures. Diversity, separation, input checks or containment can help, but none automatically establishes independence. The measure must address the actual cause or propagation path. Keep learning [Free course preview Dependent Failure Analysis (DFA)](https://iso26262.academy/features/concepts/dependent-failure-analysis) [Or test yourself with the 7-question demo exam](https://iso26262.academy/demo-exam) ## 2. Look behind the redundant boxes Start with a concrete claim: which safety requirement depends on these elements being sufficiently independent? Then inspect what they share: power, clocks, information, communication, physical environment and development assumptions. DFA considers systematic failures as well as random hardware failures. ![A shared power supply feeds both redundant channels. A supply failure may affect both; the safety consequence requires system-level analysis.](https://iso26262.academy/edge-media/p/blog/diagrams/2026/09/0724c44c-06bf-4904-a407-cdee8c1d73bf.svg) Figure 2. Two channels can still share one dependency. This is a teaching example, not a complete safety architecture. A shared supply failure could disable both channels. That does _not_ automatically prove a particular hazard occurs: the consequence depends on the safety requirement, operating situation and system response. Sharing itself is not automatically prohibited; the analysis must show whether a plausible dependent failure threatens the claim and how it is prevented or controlled. For ASIL decomposition, ISO 26262 applies decomposition to an initial safety requirement. Each resulting redundant requirement must fulfil it independently, and the implementing elements need sufficient independence. Decomposition does not relax the hardware architectural metrics or random hardware failure evaluation requirements. It is not simply a mathematical reduction of a component’s ASIL. Also distinguish **freedom from interference** from independence. Freedom from interference concerns harmful cascading effects between elements. An independence argument must also address common causes. ## 3. Connect each claim to evidence Use existing safety analyses to identify candidate dependencies. Failure Mode and Effects Analysis (FMEA) can reveal recurring vulnerabilities; Fault Tree Analysis (FTA) can expose combinations whose independence needs examination. ![Start with a safety claim, identify a plausible dependency, specify a targeted measure, and verify the measure and analysis. Revisit the chain when the design changes.](https://iso26262.academy/edge-media/p/blog/diagrams/2026/09/9bdc023d-21e2-4c8f-a1b1-f588874ce74f.svg) Figure 3. A useful DFA connects the safety claim to a dependency, a measure and supporting evidence. When DFA finds a dependency, revisit the affected analyses and assumptions. A common cause may need explicit representation in a fault tree; it does not automatically replace every individual failure event. Record why a scenario is plausible, its safety impact, the chosen measure and the evidence supporting its effectiveness. For example, memory protection can address specified access violations, but does not by itself resolve timing interference or shared power failures. Verify the analysis too, and revisit it as the architecture changes. ## Turn the principle into an engineering skill The difficult part is judging whether a dependency is plausible and whether the evidence is enough. Our subscription content on [Dependent Failure Analysis](https://iso26262.academy/features/concepts/dependent-failure-analysis) develops these decisions through interactive visuals, hardware and software discussions, a coupling-factor checklist and a worked example. **[Explore subscription plans](https://iso26262.academy/pricing)** to go beyond recognising shared dependencies and learn how to build a defensible independence argument. Last updated: 10 November 2026 Tags [asil-decomposition](https://iso26262.academy/blog/tag/asil-decomposition) [system-architecture](https://iso26262.academy/blog/tag/system-architecture) [functional-safety](https://iso26262.academy/blog/tag/functional-safety) [dependent-failure-analysis](https://iso26262.academy/blog/tag/dependent-failure-analysis) [iso-26262](https://iso26262.academy/blog/tag/iso-26262) Share this article ## Comments ## Build a stronger independence argument Explore interactive DFA explanations, hardware and software analysis, and a worked example with an Academy subscription. [Explore subscription plans](https://iso26262.academy/pricing) ## Running this analysis on a real project? Have an engineer check it, or help you build it. You get written findings on method, coverage and results. From **$1,490** with a written quote before any charge [See how we can help](https://iso26262.academy/features/consulting?service=analysis#sample) Keep learning ## Guides on this topic. The guide this article draws on, and where the topic leads next. [Browse all guides](https://iso26262.academy/features/concepts#library) - Safety analyses [Dependent Failure Analysis (DFA)](https://iso26262.academy/features/concepts/dependent-failure-analysis) Learn how ISO 26262-9 Clause 7 verifies that redundant channels and ASIL decomposition are genuinely independent, by hunting dependent failure initiators and coupling factors that let one root cause defeat several safety elements at once. [Expert](https://iso26262.academy/pricing#plan-advanced) 11 chapters - Safety analyses [HAZOP (Hazard and Operability Study) in ISO 26262](https://iso26262.academy/features/concepts/hazop) Learn to think in deviations, not just failures, using guide words applied to a system's design intention to surface hazards a checklist would miss. See how a technique born in the process industry becomes a rigorous, worksheet-driven feeding source for the ISO 26262 HARA. [Expert](https://iso26262.academy/pricing#plan-advanced) 14 chapters - Safety analyses [Markov Chains Analysis](https://iso26262.academy/features/concepts/markov-chains) Learn state-transition modeling for multi-state systems with degradation, repair, and fault tolerance scenarios. Includes an interactive Markov calculator, a dual-channel model explorer, and comparison with FTA and FMEA. 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