U3509Control Module Input Power C Circuit Low
- Generic OBD-II code · Network
- Turns on the check-engine light
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- U3509 says supply C is too low. In GM's 2016–2019 hybrid OBD tables the electric brake booster sets it when voltage sensor 2, which watches the motor driver supply, reads below 6 V for 90 s while the car travels faster than 4 mph. Unlike the A and B low codes, which are Special Type C without MIL, this one is Type A, lighting the MIL after one failing trip, because the booster motor cannot build assist without this feed. Passing requires a straight drive of at least 3.1 miles. Less than 6 V for that long almost always means an open fuse or wire, a failed connector or a deeply discharged battery rather than a brief dip. Drivers may see a brake warning and feel a harder pedal; check the motor fuse and its ground first.
- What you may notice
- MIL and brake warning on the first trip
- Harder brake pedal through missing assist
- Likely causes
- LikelyFuse of the motor supply open
- PossibleBroken wire or failed connector in feed C
- PossibleDeeply discharged 12 V battery
- RareInternal measurement of feed C faulty
- Repair
- Medium · Often possible to do yourself.Typical cost: €10 – €500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.