P0C61: Motor B resolver circuit B low uses a reference-voltage test

P0C61 is the motor-B resolver circuit-B low diagnostic in the cited 2015 GM controller. The row identifies the S2/4 reference-voltage circuit and uses a threshold below 0.5 volt. It is an electrical-range check, not a measurement of motor speed or learned angular offset.

Match the circuit designation

Circuit B refers to the resolver S2/4 path in this document. It must not be confused with the letter B used to identify the drive motor itself. The actual connector and signal mapping still require the correct vehicle service information.

With the wakeup signal on, the table qualifies 50 failing counts in 80 observations at 10.4-millisecond intervals, listing 520 milliseconds of accumulated failure time. A low value obtained while the controller is asleep is not the specified monitoring condition.

Separate low voltage from learning problems

The same controller also has learning-limit and not-learned diagnostics. P0C61's reference-voltage condition should not be replaced with an assumption that repeating an offset learn will correct it. Preserve the circuit reading, wakeup state and related resolver faults for the technician.

The source does not decide whether the low report originates in wiring, the resolver or controller circuitry. Nor does it provide a universal pinout or a replacement rule. Electrical work around the high-voltage motor and inverter requires the applicable trained service procedure.

Source and applicability

15OBDG01 Hybrid Diagnostics, cited controller and monitor only. Historical calibration limits are not universal specifications; per-code vehicle, engine and hardware applicability must be verified.

GM source, physical page 687.