Honda-Tech - Honda Forum Discussion - Knock sensor bypass

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Knock sensor bypass - Methods & Part Numbers

Man, it feels so good getting rid of that CEL. Now I can pass smog!

So if anyone ever needs to bypass their knock sensor without tripping a CEL, here is what you need to know.

First of all, you can't ground it out or replace it with a resistor. The knock sensor is not an electrical load, it actually produces it's own voltage. Your ECU is looking for a variable voltage from the sensor.

So what you want to do is mimic the voltage output. Here is a guide of what to do:

1. First, go to Radioshack and buy a piezo transducer, part #273-073. You will find it will all the buzzers because that it's intended for. It costs $1.99.

2. Flip to the back of your haynes and look at the chassis electrical pages. Find which wire going into your ECU is for the knock sensor. If you have a 96-00 civic, it is the Red wire with a blue stripe. MAKE SURE YOU DON'T MISTAKE IT FOR THE BLUE WIRE WITH A RED STRIPE. That's for your AC system. Cut the wire about 6" from the ECU.

3. Tape the transducer to your fuel rail.

3. Weave a single wire from your fuel rail back to your ECU.

4. Connect the speaker wire to the (+) wire on the transducer.

5. Connect the other end of the wire to the Red/blue wire on your ECU.

6. Connect the (-) wire on the transducer to a good ground.

So basically, the positive wire of the transducer goes to the ECU and the negative wire goes to ground. I taped the transducer to the fuel rail because that's where I found it made the most voltage (most vibration).

The transducer only makes about a half a volt at 4k rpms and the ECU usually sees about 1.5 volts. So if you try this and it doesn't work, you will have to find a better location to tape the transducer or you will have to add a second transducer to bump up the voltage.

damn how'ed you figure that out????

Re: I finally did it!!! Knock sensor bypass!! Woot! Woot! (JRciv)

your ECU was picking up a knock signal ? if you wanted to remove the CEL why don't you just unplug it ?

Since the Knock is a piezo-electric it does produces its own voltage.

Re: I finally did it!!! Knock sensor bypass!! Woot! Woot! (JRciv)

Did you ever just try to plug in a stock knock sensor or did you not have one handy?

Re: I finally did it!!! Knock sensor bypass!! Woot! Woot! (turtle-eg)

I disabled in in uberdata and desoldered the board https://honda-tech.com/forums/images/smilies/emthup.gif

Re: I finally did it!!! Knock sensor bypass!! Woot! Woot! (joetrisman)

Ok, here is what happened.

When I put my JRSC on, I smashed the sensor. When the sensor is broken or removed, it tells the ECU that your knock sensor "circuitry" is bad because it no longer gets the required variable voltage input. That means constant CEL.

Normally, not a problem. When I'm boosting I'm rockin' the P28/uber so the CEL isn't on. But to pass smog, I ziptie the bypass open and swap in my P2P. The CEL used to come back on when I did the swap, now the problem is fixed.

And I was about one day away from cracking and buying a new knock sensor for $60. And to answer the above question, I really don't know how I eventually figured this out. Probably because I did waaaay too much research and already tried just about everything else. Good thing I persevered. Everyone else said this couldn't be done.

good job, another hacker is born!

the only time where false knock is good knock!

Do you notice if the ECU is retarding timing based on this fake "knock" you are getting from the piezo?

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by xenocron »</TD></TR><TR><TD CLASS="quote">Do you notice if the ECU is retarding timing based on this fake "knock" you are getting from the piezo?</TD></TR></TABLE>

I thought he was simulating normal sensor readings to eliminate the computer from throwing a CEL?

edit: i see what you are asking...

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by xenocron »</TD></TR><TR><TD CLASS="quote">Do you notice if the ECU is retarding timing based on this fake "knock" you are getting from the piezo?</TD></TR></TABLE>

I'm pretty sure the ECU doesn't pull timing until the voltage reaches about 3v. I can't imagine this transducer putting out more than 1v at WOT.

I'm not positive though.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JRciv »</TD></TR><TR><TD CLASS="quote">

I'm pretty sure the ECU doesn't pull timing until the voltage reaches about 3v. I can't imagine this transducer putting out more than 1v at WOT.

I'm not positive though.</TD></TR></TABLE>

Nice work, man.

If you're only using this setup temporarily to get past smog, it doesn't really matter if it is pulling timing as long as the CEL stays off.

I broke that sensor before, too. It sucks. https://honda-tech.com/forums/images...s/emhammer.gif

Sonny

i broke that sensor too lol but i went obd1 so it didnt matter

just went and bought the part thanks!

bump for good knowledge

Would a CEL be triggered if the knock senser was left plugged in but was not in the block?

Re: Re: (Muckman)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Muckman »</TD></TR><TR><TD CLASS="quote">Would a CEL be triggered if the knock senser was left plugged in but was not in the block? </TD></TR></TABLE>

Probably after a while if it didnt see any voltage, it would think something is up...

Re: Re: (slow poke)

The stock honda knock sensing system isn't useful with a boosted car... heh.

Re: Re: (dustin)

Re: Re: (xavenged7x)

Just wondering, bc you can pull the oil pressure sensor out of the block and it wont trigger the oil light if its still plugged in. Thx

Re: Re: (Muckman)

Oil sender doesn't go to the ECU.. just the dash light. It gives ground when there is no oil pressure. So if you disconnect it from the block (ground), the light is not gonna show up hehe.

Re: Re: (dustin)

do a d16z6 comess with knock sensor

how accurate are the honda knock sensors?

obviously EGT/WB is the only way to go

No, the z6 does not have a knock sensor.

And from what I've read, stock honda knock sensors are a joke. They only detect knock under certain circumstances, like certain RPMs or something.

They work very well thank you.

why do you have to put it in the engine bay? isnt the least movement better but i tried it and its turning on but still throwin the code but mine is still in the car....