What is a 'knock LED'?

A 'knock LED' is a light wired up to the boost control solenoid (BCS) on the engine. The short answers to the other three questions are: Probably, no, and probably not.

Despite it's name, the 'knock LED' DOES NOT MEASURE KNOCK. [Doubters take heed: it DOES NOT.] All the LED is doing is informing you when the boost control solenoid has been tripped by the ECU. This has only the vaguest relation to knock, as there are many other non-knock circumstances that will cause the BCS to trip. This quite possibly gives the 'knock LED' the distinction of being the worst-named modification in the history of DSMs.

For details on this, read prostreets Build a Knock LED

About the only time that you can be certain the 'knock LED' is reporting knock is when it is solidly on. This indicates a last-ditch attempt by the ECU to limit boost, which can only occur when the engine is knocking for prolonged periods of time.

The LED will also flash when the ECU is attempting to limit the turbo boost (1G and 2G cars); when the ECU is "smoothing" out the normal turbo operation (2Gs); and when the car is first started and the ECU transitions the solenoid from fully closed to fully open (all turbo cars). These occurances are perfectly normal and not cause for concern.

As for the question of whether or not your engine is ok, you will only know that by looking at the operational setup and the circumstances under which you believe you may have damaged the engine. If you have been following the typical guidelines for upgrading your engine, you are probably fine. If you have upgraded your engine past the recommended guidelines or had some catastrophic event occur, your engine may be damaged. In real terms, 99% of people who are concerned about their knock LED flashing have absolutely nothing to worry about.

The Last Word: Anyone who actually takes the time to put in a "knock LED" by now is wasting their time. Not that it was ever really useful to begin with. If you truly want to measure knock, get ECMLINK.

Back in the day, there was a gentleman by the alias vanade that created was was probably the closest thing to ecmlink knock monitor for the 1G.  ECUVIEW is here for historical purposes only.