Automotive Semiconductors and Functional Safety
Which is the most appropriate example of a latent fault in ISO 26262?
- AA fault that, occurring alone, cannot be detected or controlled even by safety mechanisms and immediately leads to violation of a safety goal
- BA state in which the ECC correction circuit is broken, but nothing happens as long as no memory error occurs, so it remains unnoticed
- CA fault that was detected by a safety mechanism and reported to the driver with a warning lamp
Show answer and explanation
Answer: B. A state in which the ECC correction circuit is broken, but nothing happens as long as no memory error occurs, so it remains unnoticed
A latent fault is a fault that is not hazardous by itself and remains unnoticed by both safety mechanisms and the driver. For example, even if the correction circuit of the ECC, a safety mechanism, is broken, it does not show up as long as there are no memory errors. If a bit error then occurs in memory, it is not corrected and can lead to a hazard. Because a hazard arises only when two faults coincide, the latent fault metric (LFM) evaluates how small the proportion of latent faults is. A fault that immediately becomes hazardous is a single-point fault, and a detected fault is not a latent fault.
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