Published Date: 2021-12-15
| Postmortem Analysis | |
|---|---|
| Timeline | 1. The software failure incident involving the Subaru drive chains happened due to a programming error in the transmission control unit (TCU) [122466]. 2. The article was published on 2021-12-15. 3. Estimation: The incident likely occurred before the publication date of the article, as the recall won't commence until April 2022, and affected owners will be notified starting Feb. 7. Therefore, the software failure incident likely happened in late 2021 or early 2022. |
| System | 1. Transmission control unit (TCU) in Subaru Ascent, Outback, and Legacy models [122466] |
| Responsible Organization | 1. The software failure incident in the Subaru recall was caused by a programming error in the transmission control unit (TCU) [122466]. |
| Impacted Organization | 1. Subaru - The software failure incident impacted Subaru vehicles, specifically the Ascent, Outback, and Legacy models [122466]. |
| Software Causes | 1. The software cause of the failure incident was a programming error in the transmission control unit (TCU) that triggered premature clutch engagement, leading to drive-chain slippage and breakage [122466]. |
| Non-software Causes | 1. Incorrectly tapered holes in the housing causing tie-rod defect in 2020 Subaru Ascent SUVs [Article 122466] |
| Impacts | 1. Loss of power in the vehicles, increasing the risk of a crash [122466] 2. Drive-chain slippage and breakage due to premature clutch engagement triggered by a programming error in the transmission control unit [122466] |
| Preventions | 1. Implementing thorough testing procedures during the software development phase to identify and rectify programming errors in the transmission control unit (TCU) could have prevented the software failure incident [122466]. 2. Conducting comprehensive quality assurance checks to ensure that the gearshift selector's interaction with the TCU is properly validated before releasing the vehicles to the market could have helped prevent the premature clutch engagement issue [122466]. 3. Employing robust monitoring systems to detect early signs of drive-chain slippage and breakage, thereby allowing for proactive maintenance and repairs before incidents occur, could have mitigated the risk of power loss in the vehicles [122466]. |
| Fixes | 1. Reprogramming the potentially faulty Transmission Control Unit (TCU) [122466] 2. Reviewing the module's data for indications of chain slip and inspecting the chain guide [122466] 3. Replacing the vehicle's entire transmission if evidence of chain slip is detected [122466] | References | 1. Official NHTSA filing 2. Subaru dealerships 3. Federal authorities 4. Subaru customer service [122466] |
| Category | Option | Rationale |
|---|---|---|
| Recurring | one_organization | (a) The software failure incident related to the drive chain issue in Subaru vehicles has happened again within the same organization. Subaru is recalling 198,255 Ascent, Outback, and Legacy models due to a drive chain problem stemming from a software issue [122466]. The programming error in the transmission control unit (TCU) triggering premature clutch engagement leading to drive-chain slippage and breakage is a recurring issue within Subaru vehicles. (b) There is no information in the provided article about the software failure incident related to the drive chain issue happening at other organizations or with their products and services. |
| Phase (Design/Operation) | design | (a) The software failure incident in the Subaru recall is related to the design phase. The issue stems from a programming error in the transmission control unit (TCU) that can trigger premature clutch engagement before the drive chain is secured, leading to drive-chain slippage and breakage [122466]. This indicates that the failure was due to contributing factors introduced during the system development or updates, specifically in the design of the TCU software. |
| Boundary (Internal/External) | within_system | (a) The software failure incident related to the Subaru recall is within_system. The issue stems from a programming error in the transmission control unit (TCU) of the affected vehicles, specifically related to a premature clutch engagement triggering drive-chain slippage and breakage [122466]. The problem occurs when the gearshift selector is moved to Drive or Reverse immediately after engine startup, indicating an internal software issue within the vehicle's system. |
| Nature (Human/Non-human) | non-human_actions, human_actions | (a) The software failure incident related to the drive chain issue in Subaru vehicles was due to a non-human action. Specifically, it was caused by a programming error in the transmission control unit (TCU) that triggered premature clutch engagement, leading to drive-chain slippage and breakage [122466]. (b) The tie-rod defect issue in Subaru vehicles was due to a human action. The problem was attributed to an out-of-spec cutting tool used in the housing manufacturing process, resulting in incorrectly tapered holes in the housing that led to overtorqued nuts and potential tie rod separation [122466]. |
| Dimension (Hardware/Software) | hardware, software | (a) The software failure incident occurring due to hardware: - The software issue leading to the drive chain fracture in Subaru vehicles is attributed to a programming error in the transmission control unit (TCU) [122466]. (b) The software failure incident occurring due to software: - The drive chain fracture issue in Subaru vehicles is specifically mentioned to stem from a software issue, indicating that the contributing factor originates in the software itself [122466]. |
| Objective (Malicious/Non-malicious) | non-malicious | (a) The software failure incident related to the Subaru recall of 198,255 Ascent, Outback, and Legacy models was non-malicious. The issue stemmed from a programming error in the transmission control unit (TCU) that could trigger premature clutch engagement, leading to drive-chain slippage and breakage [122466]. The problem was not caused by malicious intent but rather by a software issue that could potentially harm the vehicles and increase the risk of a crash. |
| Intent (Poor/Accidental Decisions) | accidental_decisions | (a) The software failure incident related to the Subaru recall of 198,255 Ascent, Outback, and Legacy models was not due to poor decisions but rather a programming error in the transmission control unit (TCU) that triggered premature clutch engagement, leading to drive-chain slippage and breakage [122466]. This incident was a result of a technical flaw in the software rather than poor decisions. |
| Capability (Incompetence/Accidental) | accidental | (a) The software failure incident related to the Subaru recall is not attributed to development incompetence. The issue with the drive chains in the Subaru vehicles was caused by a programming error in the transmission control unit (TCU) that triggered premature clutch engagement, leading to drive-chain slippage and breakage [122466]. (b) The software failure incident related to the Subaru recall can be categorized as accidental. The problem with the drive chains in the Subaru vehicles was a result of a programming error in the TCU that occurred when the gearshift selector was moved to Drive or Reverse immediately after engine startup, leading to the potential loss of power and an increased risk of a crash. This accidental software issue prompted the safety recall by Subaru to address the issue and prevent any potential accidents or injuries [122466]. |
| Duration | temporary | (a) The software failure incident related to the Subaru recall of 198,255 Ascent, Outback, and Legacy models is considered temporary. The issue stems from a programming error in the transmission control unit (TCU) that can trigger premature clutch engagement, leading to drive-chain slippage and breakage. This problem specifically occurs if the gearshift selector is moved to Drive or Reverse immediately after engine startup. Subaru plans to address this issue by reprogramming the TCU, inspecting for chain slip indications, and potentially replacing the entire transmission if needed. The recall is set to begin in April 2022, and affected owners will be notified starting in February 2022 [122466]. |
| Behaviour | crash, omission, timing, value, other | (a) crash: The software failure incident in the Subaru vehicles is related to a programming error in the transmission control unit (TCU) that can lead to a loss of power in the vehicles, potentially resulting in a crash [122466]. (b) omission: The software issue in the TCU can trigger premature clutch engagement before the drive chain is secured, leading to drive-chain slippage and breakage, which can be considered an omission of the correct sequence of operations [122466]. (c) timing: The problem occurs if the gearshift selector is moved to Drive or Reverse immediately after engine startup, indicating a timing issue in the software's response to certain inputs [122466]. (d) value: The software issue results in the TCU performing its functions incorrectly by engaging the clutch prematurely, leading to drive-chain issues and potential power loss in the vehicles [122466]. (e) byzantine: There is no indication in the article of the software failure incident exhibiting inconsistent responses or interactions that would classify it as a byzantine failure. (f) other: The software failure incident can be categorized as a "premature engagement" issue, where the software incorrectly engages the clutch before the drive chain is secured, leading to potential drive-chain slippage and breakage [122466]. |
| Layer | Option | Rationale |
|---|---|---|
| Perception | processing_unit, embedded_software | (a) sensor: The software failure incident related to the Subaru recall was not directly related to a sensor error. The issue stemmed from a programming error in the transmission control unit (TCU) that triggered premature clutch engagement, leading to drive-chain slippage and breakage [122466]. (b) actuator: The software failure incident was not directly related to an actuator error. The problem was caused by a programming error in the transmission control unit (TCU) that resulted in premature clutch engagement, leading to drive-chain issues [122466]. (c) processing_unit: The software failure incident was related to a processing error. Specifically, a programming error in the transmission control unit (TCU) caused the issue by triggering premature clutch engagement, resulting in drive-chain problems [122466]. (d) network_communication: The software failure incident was not related to a network communication error. The issue was caused by a programming error in the transmission control unit (TCU) that led to drive-chain slippage and breakage, affecting certain Subaru models [122466]. (e) embedded_software: The software failure incident was directly related to an embedded software error. The problem stemmed from a programming error in the transmission control unit (TCU) that triggered premature clutch engagement, leading to drive-chain issues in Subaru vehicles [122466]. |
| Communication | unknown | The software failure incident reported in Article 122466 is not related to the communication layer of the cyber physical system that failed. Instead, the failure was attributed to a programming error in the transmission control unit (TCU) of Subaru vehicles, specifically causing premature clutch engagement leading to drive-chain slippage and breakage [122466]. |
| Application | TRUE | The software failure incident reported in Article 122466 was related to a programming error in the transmission control unit (TCU) of Subaru vehicles. This error led to premature clutch engagement before the drive chain was secured, resulting in drive-chain slippage and breakage. The issue occurred when the gearshift selector was moved to Drive or Reverse immediately after engine startup. This programming error falls under the category of a failure at the application layer of the cyber physical system, as it was caused by a bug in the software [122466]. |
| Category | Option | Rationale |
|---|---|---|
| Consequence | harm, property | (a) death: People lost their lives due to the software failure (b) harm: People were physically harmed due to the software failure (c) basic: People's access to food or shelter was impacted because of the software failure (d) property: People's material goods, money, or data was impacted due to the software failure (e) delay: People had to postpone an activity due to the software failure (f) non-human: Non-human entities were impacted due to the software failure (g) no_consequence: There were no real observed consequences of the software failure (h) theoretical_consequence: There were potential consequences discussed of the software failure that did not occur (i) other: Was there consequence(s) of the software failure not described in the (a to h) options? What is the other consequence(s)? The consequence of the software failure incident in the reported articles is primarily related to potential harm (loss of power in vehicles leading to an increased risk of a crash) and property impact (vehicles needing inspection, repairs, and potential transmission replacement). There were no reported deaths, and the company was unaware of any crashes or injuries resulting from the issue. The recall was initiated to prevent potential harm to individuals due to the software issue [122466]. |
| Domain | transportation, manufacturing | (a) The software failure incident reported in the article is related to the transportation industry. Subaru is recalling vehicles (Ascent, Outback, and Legacy models) due to a software issue that could lead to a loss of power in the vehicles, increasing the risk of a crash [122466]. The issue stems from a programming error in the transmission control unit (TCU) that can trigger premature clutch engagement, leading to drive-chain slippage and breakage, affecting the vehicles' performance and safety. The recall involves a significant number of Subaru vehicles, including SUVs and crossover wagons, highlighting the impact on the transportation sector. |
Article ID: 122466