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5v supply fail?

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  • 5v supply fail?

    I was performing some cold start tests last weekend with a SM4 v1.11. On Saturday all sensors worked perfectly, but on Sunday I discovered that my TPS, oil pressure and fuel pressure were all reading 0. I traced this back to pin 36 no longer supplying 5v. Is there a fix for that, or should I just arrange another 5v supply?


  • #2
    Have you tried unplugging the TPS + oil & fuel pressure sensors and taken a reading from the back of the ecu plug on pin 36?


    • #3
      Check the ground as well.
      He gets his lap dogs to do his talking for him. Buzzard is a good example.


      • #4
        Thanks guys. I have now performed both tasks and there's still nothing coming from pin 36. Any other suggestions?


        • #5
          Well if it was me, I'd take the ECU out of the car and power it up on a workbench using a +12v power source (or car battery) with some spare wire + spare ecu pins (normal junior timer type, and a bit of electrical tape around each connector) and use a multimeter to then test if pin 36 is supplying +5v.

          If you can provide +12v power to pins 1 + 15, and a ground from the same power source to pin 29 (these are the big 3 ecu pins furthest away from the map sensor / data port) the ECU will switch on (be very careful not to accidentally touch these wire together or onto any other pins in the connector!)

          Now use a multimeter to test pin 36 (other end to pin 22). If you have no volts then you can assume it is an ECU fault and nothing to do with a wiring issue in the car.


          • #6
            Thanks Wes, that's simple enough as I have a spare fly lead anyway. Does anyone know the max continuous current supported from the 5v supply?


            • #7
              I think it is possibly 100mA. You didn't mention the MAP and air temp sensors. Do they read correctly?


              • #8
                Originally posted by Ian View Post
                I think it is possibly 100mA. You didn't mention the MAP and air temp sensors. Do they read correctly?

                Sorry Ian, I missed your reply. Yes, MAP and air temp sensors are reading correctly.


                • #9
                  I ended up buying a 3 amp, 12v to 5v converter and feeding it in where pin 36 had been supply 5v. The wire from pin 36 is now unused. All 5v sensors have returned to normal, so it looks like I'd just overloaded it.


                  • #10
                    An SM4 has two 5v supplies, one for the internal references and pullup resistors and another for the external 5v supply pin (which tracks the internal supply so ratiometric sensors read correctly).

                    With the ECU disconnected can you do a resistance check between pins 36 and pin 29 and report the value?
                    Last edited by Chris; June 17th, 2016, 04:10 AM. Reason: For clarity


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