Cause
Wiring harness repaired incorrectly
A previous repair done badly — wrong gauge wire, a twisted joint wrapped in tape, an insulation-displacement connector crushed onto a signal line, or a splice in the wrong place. It is worth naming because the fault is not where it appears to be, and because the repair itself is invisible under a loom wrap.
High resistance is the usual result. A poor joint passes a continuity test and drops voltage under load, so the circuit works until it is asked to do something — which produces intermittent faults that resist every static measurement. Undersized wire behaves the same way, and both worsen as the joint oxidises.
Signal circuits suffer differently. A screened sensor cable repaired without restoring the screen picks up interference from whatever it runs beside, giving noise that reads as a failing sensor. Look for tape, heatshrink or a connector that does not match the loom — the evidence is physical, and finding it is quicker than measuring. Ask what work has been done, since a repair from years earlier will not be volunteered.
Typically a moderate job.
Codes this can cause (2)
Codes where this is a likely explanation first, rather than merely a possible one.
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