* Engine Control Unit (ECU) relies on the knock sensor: The knock sensor's job is to detect detonation (knocking) in the engine. The ECU uses this information to adjust the ignition timing. If the ECU receives a faulty signal (or no signal at all) from a bad knock sensor, it might enter a "safe mode" to prevent engine damage. This safe mode *could* involve preventing the engine from starting, particularly if the ECU is programmed to be very conservative in the absence of knock sensor input.
* More likely symptoms: A more common symptom of a bad knock sensor is a noticeable reduction in engine power, rough running, or a check engine light. The car might still start, but it will run poorly.
* Other possibilities: Many other problems can prevent an engine from starting. A bad crank sensor, camshaft sensor, fuel pump, or battery are much more likely culprits.
In short, while a *severely* faulty knock sensor *could* theoretically prevent starting in some situations, it's far from the most probable cause. A diagnostic test is needed to determine the actual reason for the no-start condition.
