Loss Of Isolation Check

The Loss of Isolation Check procedure is used to check the integrity of the high-voltage (HV) circuits. When loss of isolation (LOI) occurs, the HV system is no longer isolated, meaning a short circuit between the vehicle's HV circuits, and chassis ground has occurred.

1. Perform the High-Voltage Power Down procedure. Refer to ELECTRIC VEHICLE CONTROL SYSTEM, STANDARD PROCEDURE .

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2. Set a suitable multi-meter capable of measuring isolation to the isolation setting per the meter manufacturer's operating instructions. Position the probes in the correct multi-meter sockets to measure isolation, and attach an alligator-type clip adapter to the black (-) probe. Select the voltage range to be 500-volts.
   Fig 1: Power Distribution Center (PDC) Positive Test Port

   Courtesy of CHRYSLER GROUP, LLC
3. Place the red positive lead (1) of the multi-meter into the red (+) test port on the power distribution center (PDC).
   Fig 2: Multi-Meter Negative Lead Clipped To 12-Volt Battery Negative Terminal

   Courtesy of CHRYSLER GROUP, LLC
4. Clip the black negative lead (2) from the multi-meter onto the 12-volt battery negative terminal.
5. Press and hold the isolation test button (3) on the multi-meter and record the measurement observed on the multi-meter display.
   • If the measurement observed is greater than 500 kilo-ohms, the positive bus has no loss of isolation.
   • If the measurement observed is less than 500 kilo-ohms, the positive bus has a loss of isolation to chassis ground. Inspect for any visual damage and continue to step 6 to test the negative bus.
   Fig 3: Positive Lead In Negative Test Port Of The PDC

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6. Place the red positive lead (1) into the black (-) test port in the PDC.
   Fig 4: Negative Lead On 12-Volt Battery Negative Terminal

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7. Clip the black negative lead (2) from the multi-meter onto the 12-volt battery negative terminal.
8. Press and hold the isolation test button (3) and record the measurement observed on the meter.
   • If the measurement observed is greater than 500 kilo-ohms, the negative bus has no loss of isolation.
   • If the measurement observed is less than 500 kilo-ohms, the negative bus has a loss of isolation to chassis ground.
9. Evaluate the isolation readings observed for the positive bus (step 5) and the negative bus (step 8).
   • If an isolation fault has not been detected in either the positive bus, or the negative bus, the procedure is complete and no further steps are required.
   • If an isolation fault has been detected in the positive bus and/or the negative bus, locate and repair the fault.
10. After the loss of isolation has been repaired, repeat steps 1 through 4.
    NOTE:

    Although the PASS/FAIL specification for pre-repair isolation is 500 kilo-ohms, the PASS/FAIL specification for post-repair isolation is 1 mega-ohm.

    Fig 5: Multi-Meter Negative Lead Clipped To 12-Volt Battery Negative Terminal

    Courtesy of CHRYSLER GROUP, LLC
11. Press and hold the isolation test button (3) and record the measurement observed on the multi-meter.
    • If the measurement observed is greater than 1 mega-ohm, the positive bus has no loss of isolation.
    • If the measurement observed is less than 1 mega-ohm, the positive bus has a loss of isolation to chassis ground. Locate and repair the fault. Following the repair, return to step 10.
12. Repeat steps 6 through 7.
    Fig 6: Negative Lead On 12-Volt Battery Negative Terminal

    Courtesy of CHRYSLER GROUP, LLC
13. Press and hold the isolation test button (3) and record the measurement observed on the multi-meter.
    • If the measurement observed is greater than 1 mega-ohm, the positive bus has no loss of isolation.
    • If the measurement observed is less than 1 mega-ohm, the positive bus has a loss of isolation to chassis ground. Locate and repair the fault. Following the repair, return to step 10 of this procedure.