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HOMESERVICE MANUALSCHEVROLET2009TAHOE BASE, 4.8 CREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 272 (HYBRID ENERGY STORAGE SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDTC P0C77 OR P1A20CIRCUIT/SYSTEM TESTING
2009 Chevrolet Tahoe Base, 4.8 C

Circuit/System Testing

2009 Chevrolet Tahoe Base, 4.8 CSECTION Circuit/System Testing
WARNING: This page is about a different car, the 2010 GMC Yukon, 2010 Chevrolet Tahoe, and 2010 Cadillac Escalade. However, it is still accessible from the selected car via links, so may be relevant.
WARNING: 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. Ignition OFF, disable the high voltage at the drive motor generator battery. Refer to High Voltage DisablingΒ .
  2. Disconnect the air conditioning control module terminal X4 B+ (300 V) and terminal X5 ground (300 V).
  3. Test for infinite resistance between the terminals listed below and ground;
    • X4 B+ (300 V) cable
    • X5 ground (300 V) cable
    • If less than the specified value, replace the air conditioning control module assembly.
  4. Test for greater than 50k Ξ© between the B+ (300 V) terminals X4 and ground (300 V) X5.
    • If less than the specified range, test the circuits for a short between the circuits. If the circuits test normal, replace the air conditioning control module assembly.
  5. Connect the EL-48458Β  at the drive motor generator power inverter module. Refer to the EL-48458Β  installation procedure located in High Voltage System Diagnosis (EL-48458) .
    6. NOTE: Install a manual disconnect lever with a verified good fuse or a new manual disconnect lever.
  6. Install the manual disconnect lever.
  7. Connect the 12 V battery.
  8. Ignition ON, attempt to precharge the high voltage system by moving the high voltage contactor relay switch on the tester to the closed position. Verify that the hi-voltage greater than 60 V LED does not illuminate.
    • If the LED illuminates, replace the drive motor generator power inverter module.
    9. NOTE: The following tests require wearing personal protection equipment (PPE) gloves.
  9. Ignition OFF, remove the EL-48458Β  . Refer to the removal procedure located in High Voltage System Diagnosis (EL-48458) .
  10. Ignition OFF, disconnect the X1 B+ (300 V) and X2 ground (300 V) cables from the drive motor generator battery.
  11. Test for infinite resistance between the terminals listed below and ground
    • X1 B+ (300 V) cable
    • X2 ground (300 V) cable
    • If less than the specified value, replace the high voltage cables.
  12. Ignition ON, command the negative and positive contactors and the current limit relay ON and OFF with a scan tool. Listen for the contactors and relay to turn ON and OFF.
  13. Ignition OFF, visually inspect and test the drive motor generator battery internal high voltage DC cables and connections for a short to ground or an open/high resistance condition.
    • If a short to ground or an open/high resistance condition is found on the high voltage cables or connection points, replace the drive motor generator battery cable.
  14. If all the circuit tests normal, replace the drive motor generator battery assembly.
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Stop DIY work and contact a certified mechanic immediately if any of the following apply:

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