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Check engine light - knock sensor

I have a 2012 hyundai accent. The check engine light came on. The code read knock sensor. Before I could get it into a shop, it went off. It didn’t come back for 11 months. When it did come back, the same code was read. Again, it went off the following day before it could be looked at and hasn’t been seen since. The shop says that even though there is a history code, it would be hard to diagnose since it isn’t an active code. I noticed absolutely no difference in performance when the code was active. Both times it went on, the car was idling for several minutes with the ac on, and it came on as i accelerated onto a highway immediately afterwards. However, it has idled like that many other times without the light coming on as well. Any ideas?

It may simply BE detecting KNOCK… You have a small engine…with the AC On…Accelerating onto a highway… Perfect high load conditions to expect to see knock…if knock were going to occur. The fact that the light goes off on its own with an enormous gulph of time between further supports this theory.

When you know you will be loading this engine similarly…use better fuel. The Knock Sensor is simply doing its job.


I agree with Honda Blackbird, but I wanted to add that all of this could be an indication that the engine is running too hot when the A/C is engaged, because knocking is much more likely to occur when the engine is running too hot.

I would suggest that the OP check his coolant level.

Im near certain we arent using the “Best Grade” of fuel in this vehicle… No need till you know you will tax the systems harder with the AC…

I too agree with Honda. The knock sensor is detecting an occasional undesired ignition, probably from lower grade fuel than it needs, but if it’s on the original sparkplugs and has a lot of miles on it, it might just need new plugs. Carbon retains heat, and a bit of carbon buildup on a plug can cause occasional unwanted ignition.

The knock sensor is nothing but a crystal that’ll send an electrical signal when it detects a mechanical pulse that the engineers have determined is consistent with pinging or knocking. It’s called a “piezoelectric” sensor, which just means crystal that… well, what I just said.

Question: If the knock sensor detects, well, knock, doesn’t the computer just shift the timing to eliminate it?

I would think there has to be something wrong with the sensor for it to be reported as an engine error?

Or, perhaps, if the computer can’t adjust the timing and eliminate the knock, then it reports an error.

Yes, the engine retards the timing a bit… but that’s a bandaid, not a fix. And its ability to compensate is limited. The timing can only be backed off so far without introducing other more serious problems.

The sensor is there to detect a problem and trip a Check Engine Light. The CEL suggests that the sensor itself is working properly. It actually requires more than one detection to trip the light, so it’ll serve the poster well to have it looked at. Or to use a higher octane gas if he/she has been using an octane less that recommended to save money.

The computer adjusting the timing to compensate does not prevent the knock sensor from triggering a CEL. The computer reacts to the knock sensor’s signal, which also triggers the CEL. The timing adjustment is to compensate for a problem, the CEL is to tell you that the problem exists.

ok. I thought the knock sensor was for engines that were “high test recommended”, ie, normal octane is OK but not optimal.

There are several different knock sensor faults however there is a PCM software update to correct P0326, Knock sensor #1 circuit range/performance;



This bulletin provides information related to an ECM (Engine Control Module) software update for certain 2012~2013MY ACCENT(RB) and VELOSTER(FS) 1.6L GDI vehicles that may experience either of the following:

^ Check engine light for DTC P0326 - Knock Sensor 1 Circuit Range/Performance (Bank 1), or
^ Spark knock noise on heavy acceleration in warm ambient temperatures, or
^ Check engine light for DTC P0441 - Canister Purge Valve (CPV) - Incorrect CPV Flow

Applicable Vehicle: Certain 2012-2013MY Accent (RB) and Veloster (FS) with 1.6L GDI engines

I am experiencing a similar problem with my 2012 Accent SE, 96k miles.
I believe that the issue is “Spark knock noise on heavy acceleration in warm ambient temperatures” as the noise occurs only under those conditions. The dealer mentioned to me that a cleaning of the fuel system is mandatory after 50k, as these engines are “famous for having problems with the injection system” - their words, not mine. I’ve also just found that this problem can be caused by “an accumulation of carbon deposits in the combustion chambers, on piston tops and valves can increase compression to the point where it exceeds fuel octane rating.” More info here:

Read more:

Knocking can be caused by carbon accumulation in the combustion chamber/pistons. That’s true. But it would be a very unusual thing to happen, especially to a 2012 model. If that were the case you’d want to have it checked for codes associated with incorrect fuel mixture, pcv, or egr , or missing problems. No harm to have the injectors cleaned, but it seems an odd thing to say that the model’s injection system is known to have problems, as that would indicate there’s a design problem with this engine, so you’d expect it would be covered by a recall or customer interest bulletin. I have no experiende with that make but I doubt there’s a systematic problem with the fuel injection system.

Knocking on newer cars like yours is most likely caused by

  • the wrong grade of gasoline
  • poor quality or contaminated gasoline
  • ignition system problems
  • faulty knock sensor

Those are where I’d start.

Since this problem occurs so infrequently, I’d suggest someone cleaning the wire connection. Usually when the sensor senses knocking, it will retard the timing to compensate and you’ll feel a loss of power.