GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2008 🢒 Tahoe - 2WD 🢒 DTC 🢒 DTC P1AF0 or P1AF2

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 Descriptor

DTC P1AF0: Drive Motor 1 Control Module Hybrid Battery Voltage System Isolation Lost

DTC P1AF2: Drive Motor 2 Control Module Hybrid Battery Voltage System Isolation Lost

Circuit/System Description

The drive motor generator power inverter control module (PIM) contains two motor control modules (MCMs). Each MCM measures hybrid battery high voltage (HV) with several internal sensors. The MCMs test for loss of isolation (LOI) between either the HV positive circuit or HV negative circuit and vehicle chassis. The MCMs test for isolation when the HV contactor relays are closed. The battery energy control module (BECM) only tests the hybrid battery assembly for HV loss of isolation when the HV contactor relays are open.

MCM LOI is detected through the use of two high-impedance resistors and voltage measuring circuitry. The two resistors are connected in series between the HV positive and HV negative circuits. The center connection of the two resistors is also connected to vehicle chassis. The MCM then measures the voltage drop across one of the resistors. Without a loss of isolation, the MCM should measure about half of the high voltage potential. This is referred to as mid-pack voltage. The Mid-pack voltage value is then doubled by the software and displayed on a scan tool as Motor 1 Isolation Voltage or Motor 2 Isolation Voltage. When a loss of isolation is present, the motor isolation voltage display will indicate voltage that is more or less than actual hybrid battery high voltage.

Conditions for Running the DTC
    • The high voltage contactor relays are closed.
    • High voltage is greater than 50 volts.
    • Ignition voltage is 8-18 volts.
    • DTCs P1AEE, P1AF4, and P1AF5 are not set.

Conditions for Setting the DTC

The ratio between Mid-Pack Voltage and hybrid battery high voltage is less than 0.27 or greater than 1.80.

OR

    • Mid-Pack Voltage is less than 35V or greater than 975V.
    • Either above condition exists for 5 seconds.

Action Taken When the DTC Sets

DTCs P1AF0 and P1AF2 are Type C DTCs.

Conditions for Clearing the DTC

DTCs P1AF0 and P1AF2 are Type C DTCs.

Reference Information

Schematic Reference

Hybrid Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Special Tools

    • EL-48458 Pre-Charge Test Tool
    • EL-48569 Terminal Covers

Circuit/System Verification

    Important: DTC P1AE7 must test and pass before performing this diagnostic procedure.

  1. Inspect for DTC P1AE7.
    2. ⇒If the DTC is set, the loss of isolation has occurred within the drive motor generator battery. Diagnose this concern first. Refer to DTC P1AE6 or P1AE7 .
  2. Inspect for DTCs P0A78, P0A79, P0BFD, P0BFE, P0C01, or P0C04.
    3. ⇒If any of the DTCs are set, the loss of isolation has occurred within the 3-phase components. Diagnose this concern first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle .
  3. Clear the DTC information.
  4. Turn the ignition OFF for 1 minute.
  5. Turn the ignition ON.
  6. Operate the vehicle within the Conditions for Running the DTC.
  7. Retest for DTCs P1AF0 and P1AF2.

Circuit/System Testing

    Important: DTC P1AE7 must test and pass before performing this diagnostic procedure.

  1. Inspect for DTC P1AE7.
    2. ⇒If the DTC is set, the loss of isolation has occurred within the drive motor generator battery. Refer to DTC P1AE6 or P1AE7 .
  2. Inspect for DTCs P0A78, P0A79, P0BFD, P0BFE, P0C01, or P0C04.
    3. ⇒If any of the DTCs are set, the loss of isolation has occurred within the 3-phase components. Diagnose this concern first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle .
  3. Place the vehicle in the following condition:
    4. • Ignition OFF for at least 2 minutes
    • Hood Closed
    • Transmission in Park

    Important: The following sequence must be accomplished within the time stated in Conditions for Setting the DTC.

  4. Turn the ignition ON with the engine OFF.

    5. Observe and record the scan tool HPCM 300V Circuit Voltage parameter. High voltage should be enabled and Hybrid Battery voltage observed.

    Compare the HPCM 300V Circuit Voltage parameter value to the MCM 1 Isolation Voltage display and MCM 2 Isolation Voltage display. With no loss of isolation currently present, these values should all be within 20V of each other.

    ⇒If ONLY ONE MCM Isolation Voltage value is not within the indicated range, replace the PIM.
    ⇒If BOTH MCM Isolation Voltage values are not within the indicated range, continue to the next step.
    ⇒If BOTH MCM Isolation Voltage values are within the indicated range, a loss of isolation condition is not currently present. Proceed to Drive Motor Generator Phase Testing below.

    Danger: Always perform the High Voltage Disabling procedure prior to servicing any High Voltage component or connection. Personal Protection Equipment (PPE) and proper procedures must be followed.

    The High Voltage Disabling procedure will perform the following tasks:

       • Identify how to disable high voltage.
       • Identify how to test for the presence of high voltage.
       • Identify condition under which high voltage is always present and personal protection equipment (PPE) and proper procedures must be followed.
    Failure to follow the procedures exactly as written may result in serious injury or death.

  5. Perform the High Voltage Disabling procedure for servicing at the drive motor generator control module cable connections.
  6. Remove the air conditioning control module (ACCM) high voltage cable connector from the drive motor generator power inverter module (PIM).

    7. Protect the terminal ends immediately with the EL-48569 terminal covers and UL® Listed or equivalent insulation tape rated at a minimum of 600 volts.

  7. Temporarily install the PIM high voltage distribution cover.
  8. Install the drive motor generator control module sight shield.
  9. Install the high voltage manual disconnect lever.
  10. Connect the 12 volt battery. Refer to Battery Negative Cable Disconnection and Connection .
  11. Place the vehicle in the following condition:
    12. • Hood Closed
    • Transmission in Park

    Important: The following sequence must be accomplished within the time stated in Conditions for Setting the DTC.

  12. Turn the ignition ON with the engine OFF.

    13. Observe and record the scan tool HPCM 300V Circuit Voltage parameter. High voltage should be enabled and Hybrid Battery voltage observed.

    Compare the HPCM 300V Circuit Voltage parameter value to the MCM 1 Isolation Voltage display. With no loss of isolation currently present, these values should be within 20V of each other.

    ⇒If the values are not within the indicated range, continue to the next step.
    ⇒If the values are within the indicated range, replace the ACCM.

    Danger: Always perform the High Voltage Disabling procedure prior to servicing any High Voltage component or connection. Personal Protection Equipment (PPE) and proper procedures must be followed.

    The High Voltage Disabling procedure will perform the following tasks:

       • Identify how to disable high voltage.
       • Identify how to test for the presence of high voltage.
       • Identify condition under which high voltage is always present and personal protection equipment (PPE) and proper procedures must be followed.
    Failure to follow the procedures exactly as written may result in serious injury or death.

  13. Perform the High Voltage Disabling procedure for servicing at the drive motor generator control module cable connections.
  14. Remove the high voltage Battery Positive and Negative Cable Assembly (300V) connector from the drive motor generator power inverter module (PIM). Remove and retain the cable mounting block O-ring. Re-install the O-ring after testing is complete.
  15. Connect the EL-48458 to the Battery Positive and Negative Cable Assembly (300V) and the PIM connector X1 and Close the high voltage contactor relays. Refer to High Voltage System Diagnosis for Installation Procedure and usage instructions.

    16. Important: This scan tool output control could cause a loss of communication condition with the battery energy control module (BECM). In order to clear this condition you must remove the BECM fuse from the auxiliary fuse block. To avoid causing this BECM condition, ensure the following conditions are met prior to activating the scan tool output control:

       • External 12 V battery chargers are disconnected from the vehicle.
       • The output control limits are not violated when this output control is initiated. Refer to Drive Motor Generator Battery Control Module Scan Tool Information .

  16. Activate the BECM 300V Isolation Test output control with the scan tool. Observe the 300V Isolation Test Status scan tool parameter. The Isolation Test should complete within 1 minute.
    17. ⇒If the 300V Isolation Test Status parameter indicates a Passed condition, replace the PIM and Accessory DC Power Control Module (APM).
    ⇒If the 300V Isolation Test Status parameter indicates a Failed condition, continue to the next step.
  17. Disconnect the EL-48458 from the vehicle. Refer to High Voltage System Diagnosis for Removal Procedure.

    18. Danger: Always perform the High Voltage Disabling procedure prior to servicing any High Voltage component or connection. Personal Protection Equipment (PPE) and proper procedures must be followed.

    The High Voltage Disabling procedure will perform the following tasks:

       • Identify how to disable high voltage.
       • Identify how to test for the presence of high voltage.
       • Identify condition under which high voltage is always present and personal protection equipment (PPE) and proper procedures must be followed.
    Failure to follow the procedures exactly as written may result in serious injury or death.

  18. Perform the High Voltage Disabling procedure for servicing at the drive motor generator battery.
  19. Remove the high voltage Battery Positive and Negative Cable Assembly (300V) connector from the drive motor generator battery assembly.

    20. Protect the terminal ends immediately with the EL-48569 terminal covers and UL® Listed or equivalent insulation tape rated at a minimum of 600 volts.

    Important: The drive motor generator control module sight shield and the drive motor generator battery terminal cover must be reinstalled in order to complete the HVIC current loop. The BECM will not close the high voltage contactor relays if an open HVIC condition is observed.

  20. Connect the EL-48458 to the hybrid battery high voltage terminals and PIM connector X1 with the EL-48458 harnesses. Close the high voltage contactor relays. Refer to High Voltage System Diagnosis for usage and set-up instructions.

    21. Important: This scan tool output control could cause a loss of communication condition with the battery energy control module (BECM). In order to clear this condition you must remove the BECM fuse from the auxiliary fuse block. To avoid causing this BECM condition, ensure the following conditions are met prior to activating the scan tool output control:

       • External 12 V battery chargers are disconnected from the vehicle.
       • The output control limits are not violated when this output control is initiated. Refer to Drive Motor Generator Battery Control Module Scan Tool Information .

  21. Activate the BECM 300V Isolation Test output control with the scan tool. Observe the 300V Isolation Test Status scan tool parameter. The Isolation Test should complete within 1 minute.
    22. ⇒If the 300V Isolation Test Status indicates a Passed condition, replace the Battery Positive and Negative Cable Assembly (300V).
    ⇒If the 300V Isolation Test Status indicates a Failed condition, the loss of isolation has occurred within the hybrid battery between the switched side of the high voltage contactors and the hybrid battery high voltage terminal assembly. Replace or repair the Hybrid Battery assembly as applicable.

Drive Motor Generator Phase Testing

    Danger: Always perform the High Voltage Disabling procedure prior to servicing any High Voltage component or connection. Personal Protection Equipment (PPE) and proper procedures must be followed.

    The High Voltage Disabling procedure will perform the following tasks:

       • Identify how to disable high voltage.
       • Identify how to test for the presence of high voltage.
       • Identify condition under which high voltage is always present and personal protection equipment (PPE) and proper procedures must be followed.
    Failure to follow the procedures exactly as written may result in serious injury or death.

  1. Perform the High Voltage Disabling procedure for servicing at the drive motor generator control module cable connections.
  2. Remove the 3-phase cable assembly from the PIM distribution box. Refer to Generator Control Module 3-Phase Cable Assembly Replacement .
  3. Test the resistance to ground for each phase of both drive motor generators by measuring between the following points with a DMM. You should measure infinite resistance.
    4. • Phase U terminal and chassis ground
    • Phase V terminal and chassis ground
    • Phase W terminal and chassis ground
         ⇒If infinite resistance is measured, a measurable loss of isolation is not currently present. Reassemble the vehicle and retest for DTCs.
         ⇒If less than the specified value, continue with Circuit/System Testing.
  4. Remove the 3-phase cable assembly from the transmission. Refer to Generator Control Module 3-Phase Cable Assembly Replacement . Ensure the terminals are not contacting chassis ground.
  5. Retest the resistance to ground for each phase of the 3-phase cable. Measure between the following points with a DMM. You should measure infinite resistance.
    6. • Phase U terminal and chassis ground
    • Phase V terminal and chassis ground
    • Phase W terminal and chassis ground
    ⇒If infinite resistance is measured, replace the applicable drive motor generator.
    ⇒If less than the specified value, replace the generator control module 3-phase cable assembly.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Control Module References for PIM and APM replacement, setup, and programming.
    •  Drive Motor Battery Positive and Negative Cable Replacement
    •  Air Conditioning Compressor Replacement
    •  Generator Control Module 3-Phase Cable Assembly Replacement
    •  Drive Motor with Generator Assembly Removal - 1st Position
    •  Drive Motor with Generator Assembly Removal - 2nd Position