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High Voltage at 5V Supply at ECM.

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Old 03-04-2018, 07:36 PM   #1
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High Voltage at 5V Supply at ECM.

I am getting Cummins code 386, which is equivalent to the Dodge code P0643, as far as I can tell from reading the list of Dodge codes. Pin 10 of the Engine harness connector at the ECM, which supplies the 5V reference to the Engine Position Sensor, Manifold pressure sensor and the Engine Oil pressure sensor is seeing high voltage.

I backprobed pin 10 and my digital multimeter shows a rock steady 5 volts with the engine running. My scope, when set to a fast time base of 500 microseconds or faster shows an intermittent small sine wave of about 100 microsecond duration, about 4 cycles in that 100 msecs, amplitude of about 0.2 volts riding on the 5V reference. This disturbance occurs maybe once a second. The 4 cycles constitute a decaying waveform, the first cycle is the strongest at about 0.2V amplitude and the succeeding waves are smaller in amplitude. This small wave might not mean anything at all, I am only describing it because my scope is displaying it.

Does any one have further info on this code 386/P0643?
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