Network, generic (extended)

U3018 Control Module Input Power Circuit A/B Correlation

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

Where a module has two separate battery feeds, U3018 says that feed A and feed B no longer agree. In GM's 2025 body control module tables (25OBDG04B, 25OBDG03B) the two measured voltages are compared while a battery is detected and the starter is not engaged; a gap above 4 V in 4 s of a 5 s window fails the test, Type B. GM's electric brake booster in the 2016 and 2018 hybrid tables checks battery supply against the module's own supply instead and fails at a difference above 7 V within 0.01 s, Type A, because the booster's master switch needs a firm supply. In practice one feed is usually dead: GM's PIT5869/PIT5869A for 2021–2024 Tahoe, Suburban, Yukon and Escalade pair U3018 with U3505 and warm A/C when a shorted console lamp wire blows fuse F4DR of the second BCM feed.

Likely causes

Blown fuse on one of the two feeds, often from a short on a load circuit sharing it
High resistance or loose terminal in one feed wire
Weak battery causing uneven voltage drops between feeds
Faulty voltage measurement inside the module

Symptoms

  • Service engine soon lamp or system warning, depending on the module
  • Functions on the dead feed stop working, e.g. A/C blowing warm
  • Logged together with a low-voltage code for feed A or B

Repair estimate

DifficultyMediumDIY possible
Parts and labour€10–400
Time0.3–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

module power amodule power bfuse

Related codes

U3019U3006U3007U3501U3505

References: gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov, static.nhtsa.gov.