U3018 indicates that a control module has detected a correlation fault between its two designated input power circuits (often labeled A and B). The module expects both feeds to be present and within specification simultaneously; a discrepancy in voltage, timing, or continuity triggers the code.
High resistance or intermittent contact at the module's power/ground connector or in the harness between the fuse block and module is the most frequent cause.
A single fuse supplying only one of the two feeds can open or develop high resistance, breaking the correlation.
Physical damage, a poor crimp, or a splice failure on either the A or B feed creates a voltage mismatch.
Worn switch contacts or a sticking relay can drop one feed while the other remains active.
The module's onboard voltage monitoring or regulation circuitry may fail, but this is less common than wiring issues.
An outdated or incorrect calibration can misinterpret normal supply variations; this is rare and should be considered only after hardware is verified.
Rarely. The code points to a power supply correlation issue; wiring, connectors, fuses, or relays are far more common causes.
Yes. Low system voltage or excessive voltage drop during cranking can trigger correlation faults between the two power circuits.
The vehicle may enter limited operation or stall unexpectedly; diagnose and repair before regular use.
Redundant feeds allow the module to monitor its own supply integrity and maintain critical memory or safety functions if one feed is lost.