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Strange P0702 Error

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  • Strange P0702 Error


    I have this strange problem. with the transmission.(P0702 is displayed on my OBD)

    The car won't start; once I put the key on 1 position the N is not displayed on the dash; It is Flashing N (1 second or so interval).

    In this time I looked at the clutch actuator and it makes a click sound and move (left right about 2-3 mm, very slight move and then clicks and back again). It will do that all day long if I lave the key on "1" position. As the car cannot get into N, the car wont start.

    I know from my other smart that when you put the key in the ignition and put it into "1" position the clutch actuator is extending and pushes the clutch fork

    I first suspected that the clutch actuator is at fault, so I ordered a new one (second hand but told it is working). The exact same problem

    I then suspected that the clutch form might be stuck so I checked that the fork can be moved (I used a screwdriver to push and it seem to be free)

    I then suspected the wires that go to actuator, the gear motor, the gear sensor, etc. I pulled out the wiring loom and had a proper look at each wire. I could not find any wire that was damaged in any ways.

    To make the matter more complicated and more interesting I noticed that once you disconnect the battery and reconnect it. the car starts properly, runs, changes the gears as it should, the clutch actuator is working up and down as normal, the gears are changed smoothly and all it seem is resolved

    that until I stop the engine

    once the engine is stopped, and try to put back the ignition into "1" it start again, flashing N, etc etc

    but if I disconnect the battery again for a second, then starts again as there is no problem

    I can now use the car as long as I disconnect he battery after each use

    Any ideas will be appreciated as I am stuck and have no more logical answers or tests that I can carry out in order to solve for my problem

  • #2
    P0702 is usually wiring fault so suggest you check out transmission wiring again. Measure from each transmission wiring terminal to main plug on engine control unit.


    • #3
      Transmission wiring pinout. Is correct for all Smart 450 (diesel and petrol) and all Smart Roadsters.

      Column no 1 is pins at ECU connector. Example: ECU connector Pin 23 connects to pin 4 on clutch actuator. Wire colour is yellow and wire gauge is thin meaning it is part of the rotary encoder signal.
      Both clutch and gear change actuators have 6 wires. 2 provide power. 4 wires, the thin ones that break and cause trouble, transmit the rotary encoder signal.


      • #4
        The last two columns are my tick marks for having checked once by using multimeter (M/M) and twice by current injection using 21 watt test lamp and small 12 volt battery. Injecting current through the wires is best in my experience.

        The pin out diagram would benefit from by being drawn out professionally. Any volunteers?


        • #5
          Hi tolsen,
          Thank you for your very detailed response
          I will test each wire for loss of current. I did only perform a visual test (which is highly subjective)
          what I still find unusual is why each time I disconnect the battery all the components are working properly for as long as I do not stop the car
          surely if there is a problem with a wire that will stay, preventing from working as normal

          In my case if I start the car (after disconnecting the battery) the car will run for hundreds of miles, actuator going backwards and forwards tens of times, changing gears smoothly, etc
          once I stop the engine and try starting again, the clutch actuator is ticking and not engaging in N

          also, if I do not start the car and just do this:
          - switch ignition to 1, clutch actuator activated, N displayed, ready for start in position 2
          - go back to 0
          - switch ignition back to 1, clutch actuator ticking and N flashing, not ready to start in position 2

          so it is not even the start of the car, it is purely going into 1 that causes the issue, it is like ECU is only allowing one start and no more than 1

          as you pointed out I will try testing each wire with a 21W test lamp


          • #6
            Before the test, disconnect the power supply of the car (battery pack).


            • #7
              Originally posted by mottofreee View Post
              Before the test, disconnect the power supply of the car (battery pack).
              That is always good practice but I never bother. Reason: With main ECU connector disconnected there is no electrical power to transmission actuators and sensors.


              • mottofreee
                mottofreee commented
                Editing a comment
                The troubleshooting process goes from the periphery to the center.
                If applied on an input voltage of MEG / EDG not sure that it does not spoil.
                The lamp will never be broken for this ...

                You have to know exactly what is there and then there are no problems.

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