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Decompression solenoid stays activated and smokes

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  • Decompression solenoid stays activated and smokes

    Hi, anyone have the dcs stay stuck in the open/on position after the bike has started? Get hot and smoke?

    It's a brand new dcs

    I've tested every electrical switch and traced every wire and tested for continuity.

    The only thing I can't/ don't know how to check is the igniter unit.

    Any ideas?

  • #2
    I don't know anything about the DCS but I do know a coil of wire generates heat if it has current present. It's usually the armature that helps dissipate the heat. Have you checked the source of the voltage? I am assuming it would come from a relay somewhere.


    • #3
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      according to 1700 print… a fuse feeds the decompression solenoid with 12 volts and the ECU grounds the solenoid during the startup procedure (activates the solenoid)….
      there is also what appears to be a heater which is fed by the main fuse and is controlled by the throttle position sensor….

      a coil on a solenoid will not heat up if the core pin is in the field… remove the core pin… smoke the coil… unless you removed the core pin, i doubt it is the decompression solenoid…
      now the throttle position sensor appears in the control circuit for some type of heater which is part of the decompression solenoid diagram…
      that may be your smoking problem…

      have you observed the decompression solenoid for proper operation..?

      ie: starting bike… coil energized… core pin extended to the spoon….

      when bike running… core pin retracts from the spoon… if i remember correctly… a spring pushes the core pin back into the coil… (it has been a while since i have looked at that)

      if the spring is damaged, if the core pin extends too far, or if the core pin hole is swelled to not allow freedom of the core pin movement back and forth in the coil…. Coil will overheat and begin to smoke… you really need to put eyes on the decompression solenoid and perform some simple observation…

      a voltmeter is handy to troubleshoot further via wire testing to ground on the “y/b” wire… if you are convinced it is an electrical problem…


      • #4
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        This might be clearer to follow… the wire colors to the ecu are gy/r for the thermister and L/g for the decompression solenoid….

        ( I referenced a 1600 electrical diagram for the prior wire colors… )…. please forgive my error…


        • #5
          T control, I really appreciate the time and effort. Inspires me to try and help others.

          So, the core pin does extend to the spoon but it does not retract when bike is running. It will only retract if I unplug the wiring harnesses or shut the bike off. I think that's why it gets hot.

          The diagram you attached doesn’t seem to match my bike ( different wire colors) I have attached a different diagram that seems to match even though it’s from a 2006 and mine is 2007.

          The heater you mention in the diagram I believe is the carb heater. I traced back all of the wires (B/L, R/W) which go to the TPS, speed sensor, engine start switch, ignition fuse and pick up coil. The other two wires ( T/B, G/R) go directly into the igniter unit.

          Is the igniter unit and the ecu the same thing?

          Could the ecu/igniter unit be causing the dcs to not retract back in?

          The dcs itself seems to be functioning fine. I also removed the cover to the cam shaft drive gears and decompression push rods to make sure everything was moving in there.

          you know what, I haven’t put this bike into gear yet. Just started it and let it run in neutral only. Should I ride it around a little bit? Might move something and cause the dcs to retract?

          i don’t know man. Electrical stuff is not my wheelhouse.

          ​​​​​​​thanks for the brainstorming though.



          • #6


            • #7
              I'm real good at creating smoke when it comes to electrical issues.


              • #8
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                1600 wire diagram attatched…. As per your confirmation of wire colors…
                yes… the ecm/ecu is the same… that majic box under the battery tray…. It supplies the ground to the decompression solenoid…. If you have traced the wires as stated and did not find a damaged wire….
                then you might try to acquire another ecu for testing purposes…. I am unsure of the internal circuitry of the ecu and how it senses the engine running…. It would seem that the pickup coil would be the only sensor that would indicate engine run condition since the crankshft position sensor would be used for spark timing…
                wish i had more information for you…


                • #9
                  Are you getting a decompression solenoid fault code of 6 blinks?


                  • Mad Maj
                    Mad Maj commented
                    Editing a comment
                    Yeah I get the engine light code where it blinks 3 times slow then 8 times fast. I think someone here said that was a 38 code which is the dcs

                • #10
                  I think your issue is with the thermistor. Since we don't know how the ECU is programmed, we have to make some assumptions based on logic. There is a code for a decompression solenoid fault. The control unit sends voltage to the solenoid but it doesn't "know" if it has activated. If the ECU looks for a rise in temperature from the thermistor to confirm solenoid activation and shut off the voltage it would then "know" that the solenoid is working. If your thermistor was working, it would not allow the solenoid to overheat, smoke, remain energized, and then send a fault code.


                  • Chooch
                    Chooch commented
                    Editing a comment
                    According to the 1600 manual the thermistor resistance should be 68.75 to 78.75 ohms at 77 degrees F. Make sure you test it at 77 degrees because the resistance of a thermistor changes with temperature. While you are set up for testing, the resistance value for the decompression solenoid should be 1.2 ohms at 68 degrees F.

                • #11
                  I did the resistance check on the thermistor but not sure it was at 77 degrees. Not sure how to know what temperature it is at. When I tested it was warm outside, maybe around 80 degrees. The values were not in the range. I activated the dcs by turning the key on and the values started to change rapidly. I turned it off and the values remained changed. The dcs resistance was in the 1.2 range though. I think you are right about the thermistor, however this is a brand new oem dcs. I just can’t understand it. I’m going to check those resistance values again


                  • #12
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                    According to this prior post….. he already replaced the decompression solenoid …. Odds of a bad thermistor…. ???

                    of course a voltmeter would help with electrical troubleshooting…. From prior posts… he has multiple electrical issues…. Following the troubleshooting steps in the service manual would localize the problem….

                    i sincerely doubt that a solenoid coil thermister would be the ‘de-energize’ control circuit…. I would hazard a guess that the release of the ‘start’ button would de-energise the decompression solenoid… (since the motor would be running) Since he has these “electrical gremlins”… a step by step approach would be highly advised with inspection of the entire ‘starting’ circuit… including electrical plug junctions and key safety devices…. (Electrical contact cleaner is your friend…. So are tight electrical plug connections)

                    i would probably clean the battery to frame ground first since multiple electrical issues exist… a service manual would be of great benefit to him….

                    or we can continue to dance around with all these suggestions…. Not quite sure if anything has actually been resolved at this point…


                    • #13
                      What do you think the thermistor is for?


                      • #14
                        i have tested the whole electrical starting system. I have the service manual. There are not multiple electrical issues, just this dcs issue. The battery ground has been cleaned.

                        i just re tested the thermistor resistance and it reads .680 kohms. That’s 680 ohms right? I think I need to double check with another multimeter because that seems like a coincidence that it has those in the numbers because that’s similar to the range numbers. Sorry if that makes no sense


                        • #15
                          There just isn’t much information in the manual regarding the decompression solenoid.


                          • #16
                            Do you still have the old solenoid? Are you sure it was bad? Compare the resistance values between the two. Are you sure the “spoon” is adjusted properly? Maybe remove the solenoid, leave it connected, press the start button and watch the action to make sure there isn’t anything binding.


                            • #17
                              The thermister changes value with temperature… it is mounted next to a warm motor and near an exhaust pipe… think carefully about this…

                              a solenoid is a coil of wire which creates a magnetic field when energized… the pin in the middle of the coil pops out and presses the spoon when energized…. The coil will warm slightly when energized but not to the point of creating smoke if the pin is still in the center of the coil… once the smoke comes out of the coil… the center hole would become distorted and cause the iron pin..( the thing that pushes the spoon..) to drag and no longer function properly… if the pin is still free to move and not dragging… then measure the coil resistance…

                              you can check all this with a couple of jumper wires and a 12 volt battery… apply 12 volts… pin pops up… remove 12 volts pin drops down… that is electrical check… it seems that you are doing this check when you unplug it… does the pin drop down and release the spoon?…. Is the pin free to move when de-energized or is it dragging..? Is the spoon properly adjusted to prevent the pin from coming too far out of the coil…??… these are very important questions to answer…

                              on bike… remove hot wire to starter to prevent motor from turning over…( provided bike is ready to turn over with correct position of safeties) push starter switch… decompression solenoid energizes… let go of switch… it should de-energise

                              a voltmeter can check the wire going to the ECU to confirm if it is functioning… ohm from wire to ground… push start switch… 0 ohms (or close to it) … release start switch… goes to high ohms (or infinity)…

                              the thermistor should be a safety to prevent the coil from smoking in the event the iron pin comes out of the coil… (not adjusted correctly)… the response time of a thermistor would never be used to control the solenoid…. And yes… .680 k ohms is 680 ohms… use a hair dryer on it and watch the resistance change… i wouldnt think that the actual reading is critical… your outside temperature varies quite a bit over the year…thus… so does the thermistor reading…

                              the only other check on the ECU is to test a known good one…. Is there a clinic member anywhere around you with a like model bike… it doesnt take long to swap the ECU between bikes… i know you are frustrated… isolating an electrical issue can be a pain in the ass… a methodical approach is essential….. each step of the testing process will lead you to the next step…


                              • Duke
                                Duke commented
                                Editing a comment
                                Very good write-up Tcontrol!

                            • #18
                              Chooch, yes I do have the old dcs. I’m pretty sure it was bad because when I put the new one in the bike finally turned over for the first time and I had not changed anything else. I will compare to the old one though. I didn’t cut and splice the old harnesses onto the new dcs. I routed the wires cleanly back into the corrugated tubing fyi.

                              Also important note - when the old one was on there when I got the bike it also started smoking at some point when I left the key on for too long! Should the dcs become energized just by turning the key to on? That seems wrong because when it stays energized for too long is when it gets hot.

                              Tcontrol, the pin is moving freely, the spoon is adjusted properly. The pin goes in and out freely when connected and disconnected. It pops out when I turn the key to on not when I press the start button. It does not retract when bike starts.

                              i will volt check that wire going to the ecu - good idea (I did continuity check all of the wires though.

                              yes pain in the ass for sure. I’ll try to find another ecu somehow.

                              thank you two for all the effort!


                              • #19
                                Then everything seems to be pointing at a bad ECU…. 12 volts Dc applied to the DCS via a fuse with ignition in the on position. The ecu provides the ground which energises the coil at the appropriate time and removes the ground to de-energise the system…..
                                Wouldnt hurt to pull the ecu and check for damage at the plug…. Maybe some contamination or water infiltration at the harness connection can be identified……
                                What area of the country are you in?…. Maybe a clinic member can assist you with an ECU test from a working bike…


                                • #20
                                  yes I inspected the ecu and it looks very clean. I’m in Northern California, Sonoma county.

                                  also not sure if this is connected in any way but the fuel sender unit is bad. I have one coming soon.

                                  i will report back with any progress. We will figure this out eventually!


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