Electronic Solutions for Motorsport

KSC3 Detecting Knock – Reading the LEDs

4 min read
KSC Knock Sensor ECU contents view

KSC Knock Sensor ECU contents view

The KSC3 standalone knock sensor ECU has a three level output to show it is detecting knock. One part of the output goes to a LED, the other is a 0-5v signal to the engine ECU. In this article I’ll go through what the LED colours are telling us.

LED Colours – When Knock Detected

A Level 1 breach of the knock volume threshold, outputs a Blue light to the LED (and simultaneously a 0.9v* signal to the engine ECU), Level 2 Orange (2.4v*) and Level 3 Red (4.8v*).

*Numbers are approximate, using the test function in the KSC3 app will give the exact output voltage range for your install, see the KSC3 manual on the KSC3 product page for more details

Real time knock detection demo with KSC3


Assuming we have tuned our ignition timing very close to where we want it, and we have audibly verified the KSC3 is performing how we want, driving the vehicle while observing the colour emitted by the LEDs can help us further optimise our ignition timing.

Examples of Detected Knock

In this example, we will assume a

  • Level 1 breach, Blue, (as we have programmed into the engine ECU compensation map using the 0-5v output from the KSC3) will retard ignition timing by 1 degree,
  • Orange by 3 degrees and
  • Red by 6 degrees.

We will also assume we have the Indication Period set to 0.5 seconds.

Blue Only

If we are driving and we notice we regularly see the LED as Blue, at the same load and RPM, but not Orange, we could assume that 1 degree of retard is enough to stop knock in those conditions. We could use this information to retard ignition timing by 1 degree or more at this part of the map to try to eliminate the knock.

Blue and Orange

If we are driving and we see the LED emit Blue and then Orange before switching off, at the same load and RPM point, we could assume that 1 degree of ignition retard is not enough to quell the knock but 2 or 3 degrees of retard appears to be enough. In this case we could retard our ignition timing at this point by 3 degrees to see if that quells the knock ie stops the LED from illuminating. If it does, we could try 2 degrees of retard and see if that gives the desired result.

If we see orange coming on and off at the same load and RPM point, again, we could assume 2 or 3 degrees of retard is enough to quell the knock at this point and adjust our ignition timing map accordingly.


If we see Blue and then Orange and then Red from the LED, or if it goes straight to Red and the light stops at the same load and RPM range, we could assume that between -4 & -6 degrees of retard is enough to quell the knock and we could adjust our ignition map accordingly.

If we see Red and it does not go off, this tells us the KSC3 is detecting knock even though ignition is being retarded by 6 degrees. This indicates one of two things. Either we have not set up the KSC3 correctly, be it the volume threshold or knock frequency, or we have a significant issue with our ignition map.

IMPORTANT – When KSC3 engine ECU output is not being used

If we are not using the KSC3 output to our engine ECU compensation table, ie when the KSC3 is detecting knock, the ignition is not being retarded, the LED colour will escalate eg Red, Orange to Red, Blue to Orange, as long as the KSC3 is detecting knock.

The colours, if they are changing from one colour to another, may not indicate that knock is becoming more severe (although it could be). Changing colours indicate how long the knock has been occurring for and/or how severe the knock is.

In these circumstances we should lift off the throttle, as we should whenever knock is detected.


Be audibly be listening to the engine knock sensor output to gauge how severe the engine knock actually is.


If the LED goes directly to Red, we could assume the knock is breaching the Level 3 threshold. If the LED starts at Blue and goes to Red, it could be a Level 1 breach (and if it starts at Orange it could be a Level 2 breach) but this could be a dangerous assumption. Either lift the throttle and/or audibly verify the knock.

Some Words About “Level” Breaches

ALL levels of knock volume threshold breach could be damaging to the engine. Do not assume that a Level 1 breach (Blue LED) is safe.

Bad Ignition Map/Tune

This has been said before but we will say again, the KSC3 is not a device to safeguard an engine from a bad tune or other malfunction. It is a device to help tune an engine, it is not a safety device.

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