Cause
Parasitic drain flattening the battery
Something drawing current after the vehicle should have slept, flattening the battery over days. Modern vehicles have a real quiescent draw — modules stay awake for minutes and wake periodically — so this is about a draw that never falls to the expected level.
The complaint is a vehicle that will not start after a weekend while behaving perfectly in daily use, and the low voltage then produces codes across many modules at once. Measure with the vehicle properly asleep, which means waiting for the sleep timers to expire — testing immediately is the commonest error in this procedure and gives a normal-looking high reading. Then pull fuses one at a time, and expect the answer to be an aftermarket device behind the dashboard rather than a factory module.
Typically a moderate job.
Codes this can cause (1)
Codes where this is a likely explanation first, rather than merely a possible one.
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