S13 DOHC ECU Code 34

[basicmods]

Hello all. Today I decided to check my ECU for codes, as I have been getting bad mileage recently. Checked the codes and it spit out a code 33 and code 34. The code 33 is the o2 sensor, and the code 34 is the knock sensor.

After running the o2 sensor test (as described over on NICO - Does my 240sx have a bad O2 sensor?: 240sx Articles: Nissan Forums / Infiniti Forums - NICOclub (http://forums.nicoclub.com/zerothread/161680) ) the light goes on and stays on for about 10 seconds, then turns off for about 10 seconds, then turns back on..etc - indicating a bad o2 sensor. Anyway, i've got a replacement o2 sensor that I will be putting in tomorrow to fix that issue.

My question is about the code 34. Does this mean that the engine has a knock (I haven't noticed any knocking or pinging) or just that the sensor is bad? I reset the ecu code, then took a drive to the parts store to pick up the o2 sensor. After getting home, it only spit out the code 34.

Also, while a long shot, will the new o2 sensor help with the code 34 or is it the knock sensor and/or a knock.

Thanks.

[sidewaysonmy180]

i heard sometimes youl get a bad nock senser cause the wires are too old and break. so try changing the wire from knock senser to wire harness thats probably all you need. its a bitch though ill tell you that much.

[basicmods]

I guess I could try and replace the wiring first - considering a new knock sensor is 130 bucks, it's worth a shot. I heard it's kind of a pain to get to. I may just pull the intake off and do it that way, and remove all the emissions stuff while the intake is off.

[basicmods]

Well, after lookin around on ebay and the like, I can find supposedly OEM ones for about $50. Going to check with my parts guy to make sure the part # matches, and if it does I'll probably just get one of those.

Would it be possible to test the knock sensor using a timing light? Since the purpose of a knock sensor is to detect vibrations through the engine, and then retard timing if present - could I just use a timing light, idle the car, and then hit the block with a hammer while the car is running and watch to see if the timing gets retarded a bit? I'm going to check wiring with a multimeter, and possibly to the ECU to make sure I have a connection, but as old as it is, and the fact that its probably gotten pretty hot under there, I would guess that it's probably just bad.

Is there anyway to send the ECU a fake signal saying that all is good? I don't know what kind of signal the knock sensor puts out, so I don't know if i can fake the signal going to the ECU for testing purposes.

[repda916]

i bet you its not your knock sensor.
Check everything else.

[basicmods]

i bet you its not your knock sensor.
Check everything else.

What other things would throw a code 34 though? My idle is a bit low, and I have been meaning to clean the IAVC. the injectors are fine, and the car seems to drive ok, just with horrible gas mileage. The o2 sensor should help with this, but i'm wondering if the ecu was dumping extra fuel into the engine because it thought there was a knock, or because it can't tell if there is a knock or not, so it's dumping extra fuel just in case.

That being said, i think my bad mileage started back in jan. when my water pump went out and the engine overheated. It didn't stay overheated for long, as I noticed it pretty quickly and shut the car off and had it towed home. After replacing the thermo and waterpump, the car cools fine now (aside from taking a long time in the winter to warm up) but i have had bad mileage ever since. There is no loss of oil, nor any oil being burnt, and there's no coolant in the oil, or oil in the coolant, and no bubbles in the coolant while idling the car with the raditor cap off so I don't think the overheat damaged the head or gasket.

I'm thinking the knock sensor could have gotten damaged during the overheat, and because of the damage the engine started dumping extra fuel to prevent knocks (since it can't detect them). I only drive around town so i've not been too worried about the decreased mileage. If this happened, could the increase in fuel cause the o2 sensor to go out from an overly rich condition?

I'm going to try and wire a 1 mΩ in place of the knock sensor as mention in another thread and see if it still throws the code. If it does, I'll know it's something else causing it.

[s13pignose]

You can trying going to radio shack and getting a pack of 1megaohm resistors..I used 1/2 watt version. Basically it gives off the readings a good sensor would. What I did was take it and bend both ends so the whole thing looks like a staple..and stick it in the plug on the ecu wiring..the one that connects to the harness your knock sensor connects too. What I was told if you get code 55 (a ok)..it was your sensor that was bad. If you still have a 34..you wiring is bad. Been told the fact it's a shielded wire..meaning a wire with in a wire..the shield wire breaks through the insulation on the inner and grounds it out or something.

Good luck..do a search for my name as I've made a few threads of my own asking help on the matter

[yukon]

Your o2 sensor code disappeared so it might be fine.

[smelly240]

code 34 is a sensor malfunction... its either a bad knock sensor or bad wiring.

[basicmods]

I went ahead and replaced the O2 sensor, 20 bucks so no big deal. It was the orginal o2 sensor, or was dealer part, as it had the nissan logo on it. The o2 tests ok now.

The knock sensor code went away after jumping the white wire on the plug next to the temp sensors to ground. The jumpering across straight didn't work, but that's because the black wire gets grounded to the intake on the sub-harness, and I unplugged it before the ground. Had I unplugged the subharness from the knock sensor and jumpered across that, it should have done the same thing (unless the sub-harness is bad). I've got a new OE knock sensor ordered, and when I pull it off I will check the subharness and repair/replace as nessecary. I even have some coaxial sheilded cable I could use to retain the sheilding properties of the stock subharness.

The car idles much better now, and seems a bit more peppy. The manual tranny swap that is coming in the next couple of weeks should help with that as well.

Thanks a bunch everyone for your help.

[repda916]

my code 34 in my coupe was bad trans mounts
code 34 in hatch leaky injector