P0C18Drive Motor B Position Sensor Not Learned
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- 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
- Likely causes
- LikelyOffset learn not completed after replacing the inverter, motor B or its resolver
- PossibleNo high voltage at the drive motor control module, e.g. contactor fault or disconnected HV cable
- PossibleControl module needs reprogramming to enable a wide position sensor learn
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €80 – €4,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.