Network, generic (extended)

U3509 Control Module Input Power C Circuit Low

Check engine lightOn
EmissionsNot relevant
Drive cycleRequired
Limp modePossible

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.

Likely causes

Fuse of the motor supply open
Broken wire or failed connector in feed C
Deeply discharged 12 V battery
Internal measurement of feed C faulty

Symptoms

  • MIL and brake warning on the first trip
  • Harder brake pedal through missing assist

Repair estimate

DifficultyMediumDIY possible
Parts and labour€10–500
Time0.3–2.5 h

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

Parts involved

module power cpower wiringfuse

Related codes

U350AU3508U350BU3019U3013

References: gsi.ext.gm.com, gsi.ext.gm.com, law.cornell.edu.