P0C18: motor B not-learned status needs the reason for learning failure

P0C18 is the motor B position-sensor not-learned code in this GM controller. The source describes an unvalidated resolver offset with no valid stored value. It does not state that every not-learned report proves an electrically defective resolver.

Separate interruption from an unacceptable result

Learning can fail to complete if the motor moves beyond the stated speed limit, filtered DC voltage is below the required level, or the specified phase-current variation remains inadequate. A separate branch covers a completed learning attempt whose absolute offset correction exceeds 30 degrees.

These branches change the diagnostic question. Confirm whether the process lacked its prerequisites or produced an unacceptable correction before selecting a circuit or mechanical investigation.

Use the actual service learning procedure

The monitor lists key-off and wakeup conditions, an initial low-speed state, an 832 ms delay and a 300 ms learning interval. It also explicitly requires no valid stored offset. Those internal timings are not a universal key-cycle or scan-tool procedure.

Retain the learning status, available offset information and companion resolver faults. The table provides no replacement mandate or owner-level method for forcing the motor through learning. A qualified hybrid technician must follow the exact vehicle procedure, establish safe high-voltage conditions for any physical work, and verify that a valid offset was obtained. Erasing the fault does not itself validate the learned value.

Source and applicability

GM 2010 10OBDG10 Hybrid Diagnostics, cited BPCM or hybrid-controller monitor only. Historical calibration values are not universal specifications; no per-code model, engine or hardware fitment has been established. GM PDF, physical page 303.