A three-detector pulsed-neutron logging tool computes apparent oil saturation independently from near, middle, and far carbon-to-oxygen measurements and then reconciles the three estimates into a corrected value. This paper reinterprets that mandatory multi-sensor computation as an equipment-health layer. The reconciliation spread and pairwise residual pattern identify a diverging detector without adding hardware, while five supporting indicators use quantities already produced by the logging pipeline: near-wellbore correction trend, pulse-off background count rate, neutron-generator output trend, dual-source consistency, and a cross-modality residual between base and neutron-augmented saturation estimates. An illustrative nine-interval case shows the reconciliation spread increasing from 0.4 to 7.5 porosity units while the near-wellbore indicator remains within 1.00–1.04 and the near-detector background ratio rises to 1.75, isolating a detector-electronics fault rather than an environmental change. The numerical case is illustrative rather than field validation. The method provides interpretable multi-sensor diagnosis under severe downhole vibration, shock, temperature, and changing formation conditions using existing sensing and telemetry resources.

multi-sensor fusion,residual diagnosis,equipment health monitoring,pulsed-neutron logging,oil saturation,fault isolation,remaining useful life