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Old 10-15-2019, 04:37 PM   #27
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Join Date: Jan 2006
Location: NYC
Posts: 44,009

2003 L-Series 3.0L Sedan
Default Re: Aura won't crank

rochvids, in addition to a full press assistance from imadicted2u, there's a compelling issue that doesn't make sense. When you state "Again, when I try to start it, everything goes dark in the dash and the only thing I hear is the click from the relay in the BCM.", power is lost to electronics. Excluding ancillary electronics (airbags, OnStar, abs/tc/esc, etc), the ecm and bcm (including the tcm if used in Auras) are the primary electronics needed during starting and engine running. Since the bcm and ecm are intertwined due to factory security programs, both must have power when ignition is turned ON.

In everyday use, ignition is turned on to power all electronics (ecm, bcm, tcm, abd/tc/esc, airbags, etc. The tell tale indications of electronics turning on is the entire instrument panel lighting up then turn off, leaving a few indicators on (seat belt, oil, battery, etc). All indicators cycling on then off is the lamp test phase indicating the individual electronic modules are powering up and performing their own power up self tests. The bcm drives most of the indicators with the airbag and abs driving their own indicators. Once this lamp test cycle completes (less than a few seconds) and security is OFF, starting should complete with an engine startup. When you see the instrument panel indicators turn off during starting, this tells me there's a major power issue going on, disabling the bcm and ecm. Something somewhere in the power distribution circuit is disrupting power at the moment the ignition switch is turned to the START position.

Going on your descriptions, some issues to consider.

1-The battery is faulty when more power is needed to supply amperage for the starter. A partially or worn out battery will die the moment the starter is used since the starter draws anywhere from 50-150+ amps of current. All other electrical/electronic components nevr draw more than 10-15 amps when ignition is turned ON. Starting draws the most current from a battery and strains the battery cables supplying current to the starter. Battery voltage drops to as low as 10 volts during starter use but electronics will continue to run. If you are clear about lights turning of and dead silence when attempting to start, Battery and connections are of prime concern. Again, if I didn't suggest it before, is the battery in good condition or not? Any doubts should be eliminated by one of several methods; heavy duty jumper cables with a good known battery to supplement your car battery during starting, removing the battery and bringing it to your favorite auto store selling car batteries for in-store testing to ensure the battery is good, needs a charge or replacement. When power drops out during starting, the battery and cables are strained and drawing power away from electronics. Examples are the headlights dimming if turned on and starting. ELectronics will still run but drop out if battery voltage drops. Some info states voltage below 9v in insufficient for electronics and gracefully shut down on their own. Indicator lights in the instrument panel are clues to this.

The three main power connections from the battery are the red positive cable to engine fuse panel and interior fuse panel(s) and starter, one negative cable from battery to a nearby chassis stud and one negative cable from chassis stud to engine block. All other electrical connections branch off these main power connections. If you are sure main power is fine and not a battery or main power wiring, you may have to examine individual power and ground connections to the ecm and bcm........ Remember, the bcm drives most of the instrument panel indicators.

Either this problem is with main power or wiring (and possibly electronic module failure). A list of things to check requires a specific order of priorities to check before moving on to complicated (and possible) wiring and/or electronic issues. The KISS principle applies here to keep it as simple as possible before presuming (worse case) electronics failure where GM may have to determine the problem if at home diy troubleshooting fails. In my mind, keeping it simple is using a second battery to see if things still goes dark when rule out battery failure.
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