U3018 code meaning
Control Module Input Power Circuit A/B Correlation
Network system Generic code U30xx codes Check engine light
What U3018 means
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.
U3018 at a glance
- Check engine lightYes, usually on
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyMedium, DIY possible
- Typical labor0.3 to 2.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U3018
- 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
Common causes of U3018
- Most 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
- Less likelyWeak battery causing uneven voltage drops between feeds
- Less likelyFaulty voltage measurement inside the module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Module power aModule power bFuse
What each part of U3018 means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 18 | The exact fault in that area. |
What to do next
- Note U3018 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U3018
What does U3018 mean?
U3018 means "Control Module Input Power Circuit A/B Correlation". Where a module has two separate battery feeds, U3018 says that feed A and feed B no longer agree. It is a generic code, so it means the same on every make.
Is it safe to drive with U3018?
Drive gently and only to a workshop. With U3018 the car can go into limp mode (reduced power) to protect itself.
Will U3018 fail an emissions test?
U3018 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U3018 to fix?
Difficulty: medium. A typical repair takes 0.3 to 2.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will U3018 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.