CODE 34 knock sensors are plugged up. How do I test wires and the sensors?

[k4rr]

I found my rb20det subharness and plugged it up.

Next I had to fix one of the wires because it was cut.

Plugged them up and thought everything was fine.

Took it for a drive it was pulling timing..........

Came back check codes 34 came up again knock sensor........

So if I get a multimeter.

How do I test the knock sensors and the harness itself to find the problem.What values should I look for? Whats spec supposed to be?

thanks

[k4rr]

Well I replaced one of the knock sensors today.

Since I have a spare block laying around.

I replaced the knock sensor in the rear.

Then I started the car and Got 55 all good I thought.

So I took it for a test drive and it seemed ok. Brought it back home and pulled codes and got 34 again.......... I am waiting on it to cool off now. So I can change the front knock sensor.

After I change it the only thing I know to do is rewire them. Since nobody has chimed in on a way for me to test the wires......

[Darius]

My gf had this same issue with her altima and it was not her knock sensors. The code is thown when intermittent knock is detected. It turned out that one of her fuel injectors was faulty and was not firing or partially firing on each signal so it created an irregular one cylinder misfire and possibly knocked due to high AFR and pre-detonation. So I'd check your injectors out before dropping $300 on new knock sensors.

[k4rr]

My gf had this same issue with her altima and it was not her knock sensors. The code is thown when intermittent knock is detected. It turned out that one of her fuel injectors was faulty and was not firing or partially firing on each signal so it created an irregular one cylinder misfire and possibly knocked due to high AFR and pre-detonation. So I'd check your injectors out before dropping $300 on new knock sensors.

Code 34 is for knock sesnors.

It only throws that code if they are not functioning in range.

Or the computer doesnt detect them

Like say bad wiring.

Knock sensors DO detect knock. But they dont throw a cod if they do.

Only if they are bad or if the wires are bad will you get cod 34.

[Darius]

Dude I know how knock sensors work. What I'm trying to tell you about is my experience with them and the 34 code on the ECU not being specifically related to the knock sensors.

There is nothing to a knock sensor and that is why I highly doubt that one is faulty. In fact, of the three years I've bene on this board, I've never read a post of anyone's knock sensors being bad.

[mello88]

Dude I know how knock sensors work. What I'm trying to tell you about is my experience with them and the 34 code on the ECU not being specifically related to the knock sensors.

There is nothing to a knock sensor and that is why I highly doubt that one is faulty. In fact, of the three years I've bene on this board, I've never read a post of anyone's knock sensors being bad.

Happens all the time on the KA... Code 34 usually ends up being 1) KS subharness has a short or 2) KS itself is melted/bad. IIRC Code 34 means a problem with the KS itself or the wiring, that I recall I've never seen a code 34 thrown for the ECU detecting knock, in fact I think that's a separate code. Could be wrong though, wouldn't be the first time...

To test, use your mulitmeter on both ends of the KS wire, KS side and ECU harness side. Test for continuity, you should see extremely low resistance. If it's bouncing around or 0 then you probably have a short somewhere.

If you search inside the FSM you'll find the specs for the knock sensors themselves. You can use your multimeter again to test each ones internal resistance. I want to say on the KA the knock sensor should measure about 500kohms but look it up to be sure.

[Darius]

Here's the thread from the Nissan Online Mechanic forum:

zerothread?id=164747

[mello88]

^ Good read. A little OT but wth... OBD1 vs OBD2 may have changed the significance of code 34 in the ECU. On the OBD1 KA, it throws the ECU to safe mode which retards spark timing a ridiculous amount. I'd disagree with NISTECH's statement: "The effects of the knock sensor failing would be so minimal most would not know its failing."... On the KA at least, the engine will have no power past 3000 rpm or so which is usually what prompts a code reading anyways. But that's beside the point, NISTECH hits the nail on the head with:

"The code is because either there is a poor connection between the knock sensor and the harness that plugs into it or the plastic housing on the sensor itself is cracked."

[k4rr]

Well PROBLEM = FIXED

I took the plug coming off of the engine harness by the firwall that plugs into the knock sensor subharness. I cut that plug off.

then I cut the plug off my knock sensor subharness.

Then I spliced them together.

Hooked up my extra set of knock sensors and wrapped them in napkins. then sat them on my cowl and went for a drive.

no knock sesnor code.

unplugged my napkin wrapped ones and plugged my plugs to the on the block.

Went for a drive

Runs perfect!