Light Bulbs

Faulty light bulbs are the very most common problem faced by Prius owners. Normally this would suggest just how little goes wrong, if it weren’t for the disproportionate number of them that go bad.  We literally replace hundreds of bulbs each month.

The situation is worsened by unscrupulous sales; the dealer is notorious for telling people the front bumper needs to be removed to access the headlight bulb, to the tune of 2-4 labor hours, depending on the gall of the particular service writer.  Two bulbs, round trip with tax, are routinely quoted at $800+.

No wonder Gen 2 owners got pissed, sued, and ultimately won a class action lawsuit against Toyota, effectively forcing the company to subsidize the bad behavior of its dealers.  My YouTube video replacing a bulb in less than 3 minutes was viewed 100,000 times AOTB.

Some commenters describe me as a magician with small hands.  Rest assured all of my coworkers, women and men of all sizes, replace these bulbs just as quickly, as do the techs at the dealer.  So will you.

Truth is that replacing a Prius headlight is no more difficult than replacing the bulb on any contemporary car with valuable real estate under the hood.  It’s cramped!  And the first time does require a flashlight, a mirror, and a brain.

Generation Head light Tail light Mrkr F Mrkr R Brake Plate
Gen 1 9003 7443? 194 7443
Gen 2, non-HID 9003 17717
Gen 2, HID, 2004-2005 D2R 17717
Gen 2, HID, 2006-2009 D4R 17717
Gen 3 H11 LED*

On headlights:

Gen 1:

Gen 1 headlight bulbs last the longest, even though they take 9003s—regular filaments.  They perch on the back of the headlight assembly behind a rubber cover that is removed by turning counterclockwise.  It’s an absolutely standard job.

The lenses are more prone to haze; some owners will complain of diminished brightness/visibility.  While “headlight restoration” can help, it is temporary.  The only long term solution we’ve found is replacing the assemblies with new, but the expense is sufficient to discourage fixing.  You can try 9003s that are supposedly brighter; our customers report that they don’t make much of a difference.

Gen 2s, non-HID:

[pic of 9003 v. HID bulb]

Base Gen 2s did not come with “high intensity discharge” bulbs; they run the same, good ol’ 9003s.  You can spot them through the lens (see pic), or by the color/strength of the beam.

But the car goes through 9003s more quickly than any other car I’ve seen, even the Gen 1 Prius.  Why?  My totally unproven hunch is EMF from the boost converter, inside the inverter assembly situated nearby (Gen 1s don’t have a high voltage booster).  The car doesn’t have alternator diodes, and the DC/DC system is the same by generation.


The cause doesn’t really matter: it’s not like you’re going to redesign the HV system to save a $10 bulb.  Either replace the bulb or get a different car.

The important thing is to avoid cheap parts; they’ll burn out way too fast.  When our local jobber switched to a no-name brand, we had a whole swath of bulbs burn out in less than a month (some taxis in a matter of days).  We currently purchase Philips off Amazon, forty at a time.

Gen 2s, HID:

Greed, lies, and disservice: the saga surrounding Gen 2 HID bulbs portrays the industry’s worst stereotypes.  The good news?  All the customers driven from the dealer and into independent shops willing to price the replacements fairly.  Without it LG might not have made it, to which thank dealer commission structures.

HIDs are brighter bulbs made possible by a voltage-boosting ballast.  Bad bulbs will flicker, dim, and eventually go off.  Turn the lights off and on again and the same bulb will turn on.  It’s still just the bulb.

If the bulb will not turn on at all, the customer has likely coped with a bad bulb for an extended period, cycling the lights repeatedly, fatiguing the ballast, in which case they need both the ballast and the bulb.  The ballast is also prone to water damage if the headlight assembly leaks, being located on the bottom.  The proper name is “Headlight Control ECU” and the part number varies depending on D2R and D4R bulbs.

The ballast is expensive; it’s always smart to put in a new bulb and see.  If a brand new bulb doesn’t illuminate, it’s quite likely the ballast.  If the new bulb does illuminate, the ballast is OK.  99% of the time the car just needs a bulb.


Replacing the bulb:

The back of the headlight assembly has a plastic cover that needs to turn, counterclockwise as usual, to access the bulb, and it can be stubborn.  A long screwdriver or pry bar will reach the cover and allow you to turn it.  Push too hard and the tabs will break; be careful not to hit your elbow on the fender (ouch ouch ouch).  Even if Goldilocks has been in there and broken all the tabs, the cover has a flat spot further towards the bottom that will suffice for leverage.

Once the cover turns and can be pulled back, a flashlight and a mirror will reveal all.  It does take practice and feel to do it quickly (say, under 3 minutes) but there’s no doubt you can master it.  Your reward will be the near constant stream of new customers needing bulbs.

Tip: D2Rs and D4Rs have notches that match the assembly socket.  If the bulb is not installed accordingly, the base will not be flush, making it difficult to install the spring and misaligning the beam.


As you install, watch the bulb through the lens.  The ground electrode has a ceramic sheath (originals were brown) that goes at the 6 o’clock position. You can feel and see when the bulb is properly seated.

Replacing the ballast:

The ballast cannot be removed without pulling the headlamp assembly out, which does require loosening the front bumper.  Good news is that takes 5 minutes.  Remove the screw at each wheel well and the couple fasteners/clips in front of the radiator, and let it hang.

The big shielded harness (with socket) that runs from the ballast to the back of the bulb is a PITA to get out.  Remove the aiming screw so the reflector can move freely in the assembly; all the way to one side and the socket will just eke past.

Gen 2 mini bulbs:

One of the Gen 2’s biggest design flaws is mini bulbs for tail lights. They dim and/or burn out almost yearly.  Bad front markers and license plate bulbs are less likely to attract the police, but they go out just the same.  LG replaces any dim or burned out mini bulb on the house, and we check them during every maintenance service.

Gen 3 headlights:

Gen 3s take H11 bulbs installed like any other H11 bulb and take longer to get out of the packaging than to replace.  However we still get new customers coming from the dealer after hearing the bumper has to come off for hundreds of dollars.

Gen 3 marker bulbs:

Gen 3s have two mini bulbs in each headlight assembly that are nearly impossible to service on the car.  Again, for real, the front bumper has to be loosened to remove the assembly.  As a policy we currently offer one repair: replace all the front markers at once, with an option to upgrade to LEDs.