High Intensity Discharge (HID) bulbs are unlike halogen light bulbs, which simply stop working at the end of their useful life. HID bulbs nearing their service end-of-life may flicker or intermittently be inoperable — similar to a fluorescent light bulb. Some 2006-‘09 model year Toyota Prius models may exhibit an HID headlight flicker or ­intermittent operation.

Note: The HID bulb or HID ECU for a 2004-‘05 model year Prius is not compatible with a 2006 and later model year vehicle. Installing an early model year HID bulb or HID ECU on a 2006 or later model year vehicle may cause an intermittent operation or flickering of the HID bulb.

Be sure to perform all of the inspection steps below in the order listed to ensure an accurate diagnosis. It’s advisable to perform the inspection steps again to confirm any repair.

Note: In most cases, when replacing an HID bulb for an intermittent operation or flickering condition, the HID ECU does not need to be replaced.

1. Confirm that both the headlight control ECU high-voltage socket and discharge headlight bulb are securely connected. Confirm there is no ­damage to the headlight control ECU high-voltage socket or the discharge headlight bulb connector. If the headlight-control ECU malfunctions, the headlamp may shut off completely or fail to ­illuminate.

2. Using a DVOM, perform a voltage drop test across the connector that feeds power to the HID ECU (not the HID socket).

• If the reading is equal to source voltage, ­proceed to Step 3.