GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P0C17: Drive Motor 1 Position Not Learned

DTC P0C18: Drive Motor 2 Position Not Learned

Circuit/System Description

The drive motor generator position sensor is monitored by the motor control module (MCM). The MCM monitors the angular position, speed and direction of the drive motor generator based upon the signals of the resolver-type position sensor. The position sensor, or resolver, contains a drive coil, two driven coils and an irregular shaped metallic rotor. The metallic rotor is mechanically attached to the shaft of the drive motor generator. At ignition ON, the MCM outputs a 7 volt ac, 10 kHz excitation signal to the drive coil. The drive coil excitation signal creates a magnetic field surrounding the two driven coils and the irregular shaped rotor. The MCM then monitors the two driven coil circuits for a return signal. The position of the irregular shaped metallic rotor causes the magnetically-induced return signals of the driven coils to vary in size and shape. A comparison of the two driven coil signals allows the MCM to determine the exact position, speed and direction of the drive motor generator.

The position sensor is a non-serviceable part of the drive motor generator assembly.

Offset is the relationship between the position sensor and the drive motor generator output shaft. Whenever the ignition is cycled to OFF, the MCM attempts to learn the offset of the drive motor position sensor. The MCM will attempt to learn the position at hybrid wake-up (ignition ON) only if no valid offset value has ever been learned. This condition would normally occur only after an MCM reprogramming event.

Conditions for Running the DTC

Condition 1, 2, 3 and 4

    • Hybrid wake-up signal is active.
    • The MCM has not previously learned a valid drive motor position sensor offset value.

Condition 2

Motor speed is less than 20 RPM.

Conditions for Setting the DTC

Condition 1

Position sensor offset value not learned because drive motor speed is greater than 50 RPM.

Condition 2

Position sensor offset value not learned because hybrid battery voltage is less than 192V.

Condition 3

Position sensor offset value not learned because drive motor phase to phase current difference is less than 15 A.

Condition 4

Position sensor offset value not learned because offset learn value is greater than 25 degrees.

Action Taken When the DTC Sets

P0C17 and P0C18 are Type B DTCs.

Conditions for Clearing the DTC

P0C17 and P0C18 are Type B DTCs.

Reference Information

Schematic Reference

Hybrid Controls Schematics

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

  1. Ignition OFF, wait 2 minutes.
  2. Ignition ON, wait 2 minutes and then turn ignition OFF.
  3. Ignition ON, monitor DTC Status. DTC P0C17 and P0C18 should have passed last test.
  4. If the DTC has passed, clear DTC Information. No further diagnosis is necessary.

Circuit/System Testing

  1. Inspect for DTCs P0A40, P0A45, P0A46, P0A78, P0A79, P0A3F, P0C05, P0C08, P0C0B, P0C0E, P0C4E, P0C4F, P0C52, P0C53, P0C57, P0C58, P0C61, P0C62, P0C5C, P0C5D, P1B03, P1B04 or P1B0D.
  2. If any of the above DTCs are set, diagnose and repair them prior to performing this diagnostic.
  3. Ignition ON, engine OFF. Observe the HPCM 300V Circuit parameter. The hybrid battery voltage should be greater than 192V.
  4. If the hybrid battery voltage is less than 192V perform the Jump Assist procedure and attempt to successfully charge the hybrid battery. Re-test for this DTC after the Jump Assist procedure is complete. Refer to Jump Assist.
  5. Turn the ignition OFF and wait 2 minutes.
  6. Turn the ignition ON without cranking the engine. Monitor DTC Status. DTC P0C17 and P0C18 should have passed last test.
  7. If DTC P0C4E or P0C4F sets, proceed to that diagnostic procedure.
    If DTC P0C17 and P0C18 have passed, clear DTC Information. No further diagnosis is necessary.
    If DTC P0C17 or P0C18 resets, program the PIM with the latest software version and recheck for DTCs. If the DTC resets after programming or if the PIM already contains the latest software version, replace the drive motor generator assembly.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Drive Motor with Generator Assembly Removal - 1st Position
    •  Drive Motor with Generator Assembly Removal - 2nd Position