Chassis, generic

C0509 Right Front Wheel Speed Sensor A Circuit High

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

C0509 means the right front sensor line carries more current or voltage than allowed. GM's 2019 tables (19OBDG03D) set it within 100 ms when the high-side current passes 40 mA, or when the Polaris ASIC reports either sensor line shorted to battery or an overcurrent on the low side; it is Type A. That limit sits well above anything a working sensor consumes, so a stuck reading there is a wiring or sensor fault, not a speed signal. Bosch describes its active sensors as working with a two-wire interface that follows an international standard and signals by current; there the brake module feeds the sensor and reads its pulses over the same pair, so one chafed spot affects both supply and signal. Mitsubishi assigns C1063-12, a short in the front right circuit, detected within 1 s and with MIL after one trip.

Likely causes

Sensor line chafed against a battery-voltage wire
Right front sensor drawing excess current due to an internal short
Sensor supply driver in the ABS module defective

Symptoms

  • ABS and ESC lamps on immediately, check-engine lamp on some makes
  • ABS, EBD and hill start assist suspended

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–450
Time0.5–2.5 h

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

Parts involved

wss rfsensor wiring

Related codes

C0506C0507C0508C050AC0503

References: gsi.ext.gm.com, bosch-mobility.com, mitsubishitechinfo.com.