BMW E36 Blog

BMW E36 Knock Sensors

24th July 2008

BMW E36 Knock Sensors

posted in Engine, Technical Info, Tips & Tricks, Uncategorized |

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Hi all,

As you may know, I’m still having a problem with my car’s idle. I mainly have 2 problems:

1. When I start my car, the idle bounces for a while and then it becomes stable.

2. While driving, I sometimes notice that the RPM (Rotation Per Minute) moves down until it reaches 200 or maybe less then it comes back again especially when I’m pressing the clutch pedal.

After running an extensive research about these problems, I’ve found many solutions or you may call them suggestions and they’re all over the forums. The solutions for a perfect idle in a BMW E36 are:

1. Cleaning ICV (Idle Control Valve): A very straight forward task. This unfortunately didn’t solve my problem completely but it helped a little bit.

2. Checking/Replacing the TPS (Throttle Position Sensor): I tried to replace it, but nothing has changed.

3. Check for vacuum leaks: Just buy a carborator cleaner can and while the engine is running, spray it around the engine and make sure to listen to the engine sound and see if you can detect any change in the engine’s idle. If anything has changed, it means that you have a vacuum leak. This didn’t result in any problems in my case.

4. Check the ignition coils: I didn’t find any problems with this either.

With these options out of my way, I’m left with a knock sensor error code when I check my car for problems. Actually it’s the 2nd knock sensor which is located in the left side of the cylinder block. For those who don’t know what a knock sensor is, it’s a sensor used to monitor the combustion chamber for engine-damaging knock (according the the Bentley Manual). Unfortunately, the second knock sensor requires removing the upper section of the intake manifold to replace it. So, as you can see, it’s not a very straight forward task, so I took the car to a mechanic and he replaced it (I suggest you do the same if you have the same problem). Now, the knock sensor is working properly. I also asked him about the DISA valve and it turned out that I had a vacuum leak that prevented it from working properly.

Now, after I fixed both problems, I got rid of the second problem completely. Now, I need to do more research about the first problem. I know it’s not going to be that simple and I will need to dig deeper before I have my perfect idle. But I’m not going to despair…

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There are currently 18 responses to “BMW E36 Knock Sensors”

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  1. 1 On July 24th, 2008, Johnny said:

    Hi Tony!

    If you could provide me with your email, I would send you the photos of my car, I promised to send nearly a month ago :p

    Take care,

  2. 2 On July 25th, 2008, Guetzer said:

    Hey, I had the same problem with my car, turned out to be the camshaft sensor. 🙂
    good luck!

  3. 3 On July 25th, 2008, Tony Sticks said:

    @Guetzer: You know something you may be right. My camshaft sensor is stripped out. But it’s doesn’t throw an error when I run the diagnosis. Did your camshaft sensor throw an error when you had that problem?

  4. 4 On July 25th, 2008, Tony Sticks said:

    @Johnny: My email address is tonysticks *AT* bmwe36blog *DOT* com

  5. 5 On July 26th, 2008, Guetzer said:

    Yeah, my camshaft sensor gave an error on the diagnosis.

  6. 6 On July 26th, 2008, Tony Sticks said:

    @Guetzer: Mine doesn’t. I will try to replace it and see if that helps…. thanks anyway for the help.

  7. 7 On July 27th, 2008, Guetzer said:

    Sure man! no problem 🙂 hope it works!

  8. 8 On October 3rd, 2008, Libour said:

    Hi everyone,
    I have got the same trouble with my e36 318iS. But there is no error which is related to knock sensors in diagnostic. sometime there is only error of vacuum leak and lambda sensor. My mechanist has tried to replace both – all the intake manifold and lambda sensor. It was still the same. He doesn’t belive me it could relate with the knock sensor. What do you think about? Tony, have you already got rid your problem completly of? If you have, what was the problem? thank you for any comments! Libour

  9. 9 On October 6th, 2008, Tony Sticks said:

    @Libour: Honestly, replacing the knock sensor didn’t solve the problem completely but it definitely enhanced the idle. From your description, you say that you’re getting errors for lambda sensor and vacuum leaks. So, I suggest you keep looking there. I also suggest checking the TPS (Throttle Position Sensor) and Cleaning your BMW E36 ICV (Idle Control Valve). Replacing the knock sensor(s) is NOT an easy task and you should be 100% sure it’s not working before replacing it.

  10. 10 On November 25th, 2008, Herman said:

    @Tony and the other experts here: How many knock sensors are there on a E36 M42 (318iS Oct/1995) engine ??
    I can see the one close to the front on the left (I guess for Cyl 1-2). I removed the top of the intake manifold.
    Looking down from the top and side, I cannot see something that makes out a second knock sensor.
    The OBD-I shows code 1446 which is knock sensor for Cyl# 2-3.

  11. 11 On November 26th, 2008, Tony Sticks said:

    @Herman: The M42 engine has 2 knock sensors only. One for cylinder#1&2 and the other for 3&4. The error code that you should be looking for is either code 1225 or 1226 for knock sensor 1 or 2 respectively. I hope this helps.

  12. 12 On December 4th, 2008, Herman said:

    Thanks Tony, I made a typo with 1446, should be 1226. Now I realize that
    I have to remove the manifold (not just the upper part) to get to
    the #2 knock sensor. That’s a job I should plan carefully before proceeding.
    On an other note, the intermittent check engine light and high fuel consumption,
    which made me look up the OBD-1 code in the first place, turned out to be the
    Oxygen Sensor, in use for the last 200.036 KM.

  13. 13 On December 8th, 2008, Tony Sticks said:

    @Herman: Ah… I see. Good luck with the knock sensor #2 replacement. It’s a real hard job to do.

  14. 14 On October 5th, 2011, Jeremiah said:

    Hi Tony, I was wondering why you said replacing knock sensor #2 is such a hard task. Is #1 easier? You did a write-up on cleaning the idle control valve, which requires removing the upper intake manifold. The Bentley manual says that you just need to remove the upper section to replace the knock sensors. They just bolt onto the engine block and then have an electrical connection. I have a ’95 318is that has a #2 knock sensor code (1226). I already bought a new knock sensor, but realized I probably need new gaskets as well, so it’s on hold until I get those.

  15. 15 On November 16th, 2011, Ahmed said:

    Guys i have E36 318is M42 and the OBDII shows that i have both Knock Sensors beside that My car Smell Rich (CO) inside the Cabin so I changed the Knock Sensors and checked them on OBD but they are still there nothing Change!!!!!! any Help what is messing with me here or could be something else and the OBD read it as Knock Sensor??

  16. 16 On November 16th, 2011, Jeremiah said:

    Ahmed: Disconnecting the battery will clear any codes. I had my battery disconnected when I changed mine last week, and now the codes are gone. Try disconnecting and reconnecting your battery and then drive it for a few days and see if the codes come back. You have to drive it a while for the computer to find out if there’s any problems still there though. It does this only when it it reaches full operating temperature and stays there for a while.

  17. 17 On November 17th, 2011, Ahmed said:


    I did Erase all Faults and drived the car for couple of KM then checked it again and those 2 errors came again:
    Knock Sensor 2
    Knock Control out of Range
    What does that mean and already i changed both knock sensors!!!
    please help me out

  18. 18 On November 17th, 2011, Jeremiah said:

    Well you would need to drive it more than a couple km to clear the codes. Take it on a 30 minute drive or just to be really sure drive for 30 min or more for a few days. It took the computer in my car a few trips over a few days to smooth the engine out, I guess it needed to recognize the new working sensors and adjust to that. I didn’t notice a lot of difference right after I changed them, but now I do. I haven’t heard of “knock control out of range.” Mine was giving me code 1286 “knock control test pulse”, which may be the same thing. Are you sure all faults were erased? Did you check right after you reconnected the battery to see if they were gone? Did you use the OEM brand, Bosch? And are you sure you hooked them up correctly? I know it’s possible to hook the 2 sensors up backwards.

    Oh and your car most likely has OBDI if you’re in the US, the M42 engine was installed in the 318 up to 1995, the last year for OBDI.