NewGuy19 Posted May 11, 2009 Share Posted May 11, 2009 I have a 1990 LS with 145,000 miles on it. I started my car up today after letting my roommate take it home over the weekend and noticed I had a check engine light on. Codes that showed up were as follows: 52 - No. 1 knock sensor signal 53 - Knock control signal 55 - No. 2 knock sensor signal I have no idea what would make both knock sensors throw a trouble code at the same time. But I talked to my roommate and he said he filled it up with regular 87 octane gas because it was $0.23 a gallon cheaper. I have always run premium in the car and so did the previous owner. Is it possible that my computer is just slow in picking up the signal from the sensors since its been so long if ever that there has been anything but 91 octane run in the car? Also I disconnected the battery to erase the codes and see if it was just a fluke but after about 20 seconds of running the light came back on. The car still runs and drives just as smooth as ever as if there were nothing wrong with it. I have done some searching through old posts but have not found anything similar to my problem. Quote Link to comment Share on other sites More sharing options...
NewGuy19 Posted May 13, 2009 Author Share Posted May 13, 2009 Bump it back up to the top. Anyone have any ideas? I'd like to take care of any work before I take it in to get painted on monday. Don't wanna mess up my nice new bumpers after that. Quote Link to comment Share on other sites More sharing options...
curiousB Posted May 13, 2009 Share Posted May 13, 2009 Well I doubt it has anything to do with the fuel. There are numerous examples on this site and elsewhere of users running regular when premium is called for. I've done it for > 1 year and no problem. Could it just be a connector or cable fault. Its a bit mysterious that the code is both sensors at once plus the control signal. Maybe a connector wiggled free or has become corroded so connections are poor. Just plugging and unplugging the connector pair may be enough to get a better connection (at least temporarily). You might want to search on knock sensor as I recall other people have had trouble with these sensors. Quote Link to comment Share on other sites More sharing options...
NewGuy19 Posted May 13, 2009 Author Share Posted May 13, 2009 Thanks for the reply. I know there is nothing wrong with running regular gas through the motors as the knock sensors are there to adjust for that in the first place. I just find it funny that both sensors threw a code right after he filled it up with regular gas but there are no noticeable problems. I have put over 300 miles on the car in the last two days for work and plan on filling it up tomorrow to see if anything changes, maybe disconnect the battery and see if the codes show up again with the new gas. I called up the local Toyota dealer to see if they could help me out and they suggested that perhaps the sensors are both bad but the car never picked up on it because there has never been anything but premium gas in the car. It just seems to me that even while running the same grade gas there will be enough variance where the sensors would have to adjust things a little bit. I have read through many posts on here about knock sensors however none of them seem to be similar to this problem. I guess if worst comes to worst I can take everything apart this weekend and replace both sensors and connectors, and while I'm in there do the starter as well just to avoid doing that job further down the road. Quote Link to comment Share on other sites More sharing options...
curiousB Posted May 13, 2009 Share Posted May 13, 2009 I am just guessing but I would zero in on the ground signal to both sensors. It is the common line that ties sensor and control signal. If it were corroded and not making a good connection it could create such a result. I would start with the connection back at the ECU as that is where it is common before it splits to the separate knock sensors. I am not familiar with the wiring configuration of this car but if there is another connector pair enroute to knock sensors I'd pull that plug apart too. Maybe get some of that electronic contact cleaner spray and spray some on each end of connector when you have them apart. I really doubt it’s the actual sensors because as you note how likely is they both failed at the exact same time? Highly suspicious. My 2 cents is a cable problem between sensors and ECU. Also might be a very inexpensive thing to try before you start buying new sensors. Good luck. Quote Link to comment Share on other sites More sharing options...
NewGuy19 Posted May 13, 2009 Author Share Posted May 13, 2009 That sounds like a logical place to start. But its going to have to wait a bit I'm afraid. I decided to go out and break 3 bones in my hand last night instead of finishing up some work. So my car fixing days are done till I get my cast off. Or regain the use of my fingers. Quote Link to comment Share on other sites More sharing options...
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