U3509 code meaning
Control Module Input Power C Circuit Low
Network system Generic code U35xx codes Check engine light
What U3509 means
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.
U3509 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 repairAfter a drive cycle
Symptoms of U3509
- MIL and brake warning on the first trip
- Harder brake pedal through missing assist
Common causes of U3509
- Most likelyFuse of the motor supply open
- PossibleBroken wire or failed connector in feed C
- PossibleDeeply discharged 12 V battery
- Less likelyInternal measurement of feed C faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Module power cPower wiringFuse
What each part of U3509 means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 09 | The exact fault in that area. |
What to do next
- Note U3509 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 U3509
What does U3509 mean?
U3509 means "Control Module Input Power C Circuit Low". U3509 says supply C is too low. It is a generic code, so it means the same on every make.
Is it safe to drive with U3509?
Drive gently and only to a workshop. With U3509 the car can go into limp mode (reduced power) to protect itself.
Will U3509 fail an emissions test?
U3509 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 U3509 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 U3509 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.