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Old 08-15-2021, 01:03 AM   #3
fdryer
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Join Date: Jan 2006
Location: NYC
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2003 L-Series 3.0L Sedan
Default Re: 2001 Saturn L300 - v6 3.0 Liter - ECU Question for someone! [Which Way]

Hopefully the battery negative cable was disconnected before disconnecting the ecm cables to remove the ecm. Battery negative must be disconnected before reconnecting the ecm cables to prevent any electrical short occurring from reconnecting one or both connectors incorrectly. It's easy to put multiple pin connectors on incorrectly and bend/damage pins. At least two wires are live at all times when battery cables are connected for the ecm keep alive memory holding emissions parameters. When a reset is performed from a reader, battery cable disconnect or pulling ecm fuse, live power to memory is removed to erase it. Factory default parameters are used as the engine learns new parameters and written into memory while driving. Disconnecting battery negative before disconnecting or reconnecting the ecm and other electronics prevents live 12v on any wire from inadvertently connecting to an incorrect pin from misalignment when disconnection/reconnection occurs, possibly causing damage to a circuit.

In addition and just a guess on my part as I never disconnected my ecm, the two multiple pin connectors may be keyed to prevent them from incorrect matings. You'd have to examine each male and female connectors for either a metal or plastic pin that fits only into the female terminal with a mating hole or tabs around the plastic connector perimeter only fitting into its matched female terminal.
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