ECU Error Code On The Detonation Sensor Circuit and Unplugged Cables

Discussion in 'Technical' started by gregzilla, Apr 23, 2019.

  1. gregzilla

    gregzilla Member


    I have had an issue with the car since I got it few years ago where I would be driving it and all of a sudden the revs would jump up about 800k and then after anywhere from 30sec to a couple of minutes it would drop down again. This was irregular and didn't happen all the time

    Recently, I would start the car and all of a sudden I would be missing 3rd gear in my auto. I would restart the car and all would be fine.

    Now I have totally lost 3rd gear.

    I did a diagnosis on the ECU and it came up as error code 34 which is the Detonation Sensor Circuit (I believe it's also called the Knock Sensor)

    So after a quick check on YouTube I went on the hunt for the part which showed it at the back of the engine towards the middle and I found this.


    A bunch of wires not connected and I couldn't see the sensor anywhere.

    The top red wire looks like it's going to the bottom of the engine. and the other 2 I have no idea where they belong. Is that spare harness supposed to connect to the sensor that I can't find?

    A quick look around and I also found a small skinny hose that seems to have been broken off as well


    With the error code 34, does that mean I need a new sensor and does it even run without one as I can't seem to see it anywhere?

    Where is that small hose supposed to connect to?

    It's a '89 auto non-turbo.

    Thanks in advance

  2. rob260

    rob260 Administrator Staff Member

    The easiest way around your code 34 is to bypass the sensor

    It won’t help your auto though -I haven’t had a heap or experience with autos but if you don’t remember the last time it was serviced that may be a good start.

    The mystery hose may well run to a nipple just under that throttle body.
    Last edited: Apr 23, 2019
  3. gregzilla

    gregzilla Member

    Thanks for the reply Rob,

    The the bottom right hand plug in the first image, do you think that actually connects to the knock sensor?
  4. rob260

    rob260 Administrator Staff Member

    Yes that looks like the detonation sensor harness and someone has done a hack job of replacing a broken plug.
    gregzilla likes this.
  5. Martin Williams

    Martin Williams Well-Known Member

    Looking at the state of your engine wiring I'm surprised that don't have a few more problems. I would suggest that you go through all the wiring and connectors and repair and clean. Your car is 30yrs old and these car are known to get a a lot of corrosion in the connectors and where wiring connects to the pins of the connectors. With your detonator sensor it looks to me as though someone has done or attempted to do the bypass and the 1Mohm resistor has fallen off. With you loss of 3rd gear, I suggest that it is electrical/control otherwise you would not have recovered this gear after a restart. Same issue with your engine idle. Sorry theres no easy fix, get in there and check and clean all connectors. Plus if you live close to another forum member maybe you could get them to assist you.
    gregzilla likes this.
  6. gregzilla

    gregzilla Member

    Hi Martin,

    Thanks for your reply.

    The connectors do have a bit of green film on them. Is there a recommended way to clean them?
  7. gregzilla

    gregzilla Member

    Ok, thanks for that.

    I do have a spare harness so I'll see if I can sort that out
  8. Cliff

    Cliff Member

    These are the products I use on my electrical connectors:


    gregzilla likes this.
  9. gregzilla

    gregzilla Member

  10. Martin Williams

    Martin Williams Well-Known Member

    Good luck. Remember you have at least three separate problems here, don't expect them all to disappear very easily. Welcome to the world of 300zx. They've cost me two marriages and fried my brain, but I love them!
    Gunwarm and gregzilla like this.
  11. kickerzx

    kickerzx Member

    It went up to 800k huh? I would actually pay to see that... From a safe distance obviously
    gregzilla likes this.
  12. gregzilla

    gregzilla Member


    I got the auto sorted out. It turns out it was the auto computer that was causing the issues and also it turns out the idle plug wasn't even plugged in.

    Got one from the Facebook group for $50 and works like a charm.
    Cliff likes this.
  13. tjleilo

    tjleilo New Member

    Could you quickly explain how to install this? Where doesn’t it plug into?
    gregzilla likes this.
  14. rob260

    rob260 Administrator Staff Member

    Instructions are all available via the ad I linked to.
    gregzilla likes this.
  15. tjleilo

    tjleilo New Member

    Oops! I overlooked it yesterday. My bad! Thank you!
  16. tjleilo

    tjleilo New Member

    Final question. Would this also work on an American 300zx? I don’t know if there would be any differences in design that would prevent this from working.
  17. rob260

    rob260 Administrator Staff Member

    No probs and yes it would

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