Powertrain, generic · Hybrid propulsion

P0C18 Drive Motor B Position Sensor Not Learned

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P0C18 is the motor B version of P0C17: the resolver offset of the second motor has not been learned and no valid earlier value is stored. GM performs the learn at key-off; it fails if motor speed exceeds 50 rpm, DC voltage stays below 192 V, phase current stays below 15 A or the learn takes longer than 1.4 s. The Volt tables rate it Type A, one trip, the 2012 two-mode trucks Type B, two trips. GM bulletin 21-NA-218 notes that when P0C17 and P0C18 set together, a programming event is needed to allow a wide position sensor learn, and that missing high voltage at the drive motor control module can be the reason. P0C4F reports a learned value beyond its limit.

Likely causes

Offset learn not completed after replacing the inverter, motor B or its resolver
No high voltage at the drive motor control module, e.g. contactor fault or disconnected HV cable
Control module needs reprogramming to enable a wide position sensor learn

Symptoms

  • Malfunction indicator lamp after a repair or module programming
  • Reduced propulsion or vehicle will not enter ready mode
  • Motor B unavailable for driving or charging

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€80–4,000
Time0.5–8 h

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

Parts involved

drive motor b position sensorhybrid control module

Related codes

P0C17P0C4FP0A45P0A46

References: gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov.