U3018Control Module Input Power Circuit A/B Correlation
- Generic OBD-II code · Network
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- 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
- Likely causes
- LikelyBlown fuse on one of the two feeds, often from a short on a load circuit sharing it
- PossibleHigh resistance or loose terminal in one feed wire
- RareWeak battery causing uneven voltage drops between feeds
- RareFaulty voltage measurement inside the module
- Repair
- Medium · Often possible to do yourself.Typical cost: €10 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.