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    Need help with p0203 code

    SES light plus rough idle, checked code and got p0203. Sent out fuel injectors for cleaning, re-installed and car felt great. Next day SES light, rougher idle and p0203 code.

    I will swap injectors around to check it’s not #3 but beyond that not sure what do next. Do I go straight into purchasing a an injector wiring harness loom off eBay or do I buy a DME and flash it myself? Any input is appreciated.

    Wiring Harness.
    Wire Harness. Oem 2015-2020 BMW 2 3 4 Series F3x F8x M2 M3 M4 Harman Kardon Mid Range Speaker. Engine Computers/KEY SETS. OEM 2004 Dodge Ram 2500 3500 5.9L Cummins Engine Wiring Harness. OEM 2015-2020 Ford F150 3.5L Engine Wire Harness 4WD XLT HU5T12C508J.

    #2
    Bump

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      #3
      Bump, need help. Any input is appreciated.

      Comment


        #4
        You have a voltmeter?
        The injector connector has 2pin: one is 12v when key turned on, and the 2nd pin is 12v and drops to 0v when DME injects fuel.

        To test: disconnect the big black cable off the fender 12v jumper post, to prevent starter accidentally cranking with your hand in there. Car in neutral.

        key turned on, check one pin for 12v supply and this pin should always be 12v when manually turn the crank CW. The other pin should be mostly 12v but it's pulled down near 0v while turning the crank manually.

        Report back.

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          #5
          Thanks for the advice. Is this what you are referring to disconnect? And when you say crank manually, are you referring to do so via the crank pulley or crank with the key?

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            #6
            Originally posted by Rawbin24 View Post
            Thanks for the advice. Is this what you are referring to disconnect? And when you say crank manually, are you referring to do so via the crank pulley or crank with the key?
            Yes that jumper post cable. With the cable disconnected the starter is disabled.

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              #7
              Originally posted by sapote View Post
              To test: disconnect the big black cable off the fender 12v jumper post, to prevent starter accidentally cranking with your hand in there. Car in neutral.

              key turned on, check one pin for 12v supply and this pin should always be 12v when manually turn the crank CW. The other pin should be mostly 12v but it's pulled down near 0v while turning the crank manually.​.
              I found out today that manually turning the crank doesn't trigger the ignition coils for sparks, so I think the same is for injectors. You need to use the key to crank to trigger the injectors to be sure.

              I think it's a safety design so the engine not accidentallly start running when tech manual crank during testing. The DME needs to see above a threshold rpm for it to fire the sparks and injectors.
              Last edited by sapote; 03-16-2025, 11:46 AM.

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                #8
                Originally posted by sapote View Post

                I found out today that manually turning the crank doesn't trigger the ignition coils for sparks, so I think the same is for injectors. You need to use the key to crank to trigger the injectors to be sure.

                I think it's a safety design so the engine not accidentallly start running when tech manual crank during testing. The DME needs to see above a threshold rpm for it to fire the sparks and injectors.
                Thanks for the follow up. And after testing and confirming with the voltmeter, do I replace the entire wiring harness as shown in the eBay link? It seems like a pain since it snakes under the block and intake manifold.

                Comment


                  #9
                  Originally posted by Rawbin24 View Post

                  Thanks for the follow up. And after testing and confirming with the voltmeter, do I replace the entire wiring harness as shown in the eBay link? It seems like a pain since it snakes under the block and intake manifold.
                  The code points to #3 injector, so depending on what your test result is, maybe just need to repair one wire (add a new wire) from DME to injector connector, not needing to replace the whole harness.

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