My 2012 Prius Four has reached 120,000 miles and symptoms of rough idle, cold start rattle, decreasing fuel efficiency and sporadic loss in power (especially during acceleration), has become almost a once-a-week routine. I figured it is time to replace the spark plugs. I am having major service as recommended by Toyota done to the Prius sometime this month and figured I'd shell out an extra $50~$100 to have them replace the spark plugs at the same time, so I called my dealer and requested a quote. My jaw basically dropped. I was quoted $290 and as a courtesy, the service lady offered $50 off, still $240. I called another dealer that I've been going to since 2012 and was quoted even higher at $368!! There is no way I am paying ~$300 to have $40 worth of parts changed so I decided to change it myself. After changing the spark plugs, fuel efficiency increased and displaced power from the Prius has returned. Stepping on the gas doesn't feel like the Prius is struggling and no more cold engine rattle from the ICE during warm up cycle.
For this project, I used NGK (4912) ILKAR7B11 Laser Iridium Spark Plugs. They are pre-gapped to Prius spec (1.0-1.1 mm). Depending on where and when you buy them, they cost between $9.00 ~ $11.00 each. You'll need four.
The entire spark plug replacement process costs about $45 in parts (4 spark plugs, 1 packet of anti-seize grease) and a bottle of ice cold beer. The entire procedure took me exactly an hour and 30 minutes while taking photos.
Here's a DIY guide on how to change the spark plugs from your 3rd gen, 2010-2015 Toyota Prius. Be sure to read the entire guide completely before attempting.
Tools and Materials Needed
- 9/16 magnetic spark plug socket
- 14 mm socket
- 10 mm socket
- Flathead screwdriver
- Needle nose pliers
- Anti-seize grease (optional)
- 4x NGK (4912) ILKAR7B11 (4912) Laser Iridium Spark Plugs. These are pre-gapped.
Windshield Wiper Cowl Removal Instructions
Let's remove the wiper arms to start. Begin with the driver side wiper. Remove the the cap at the base of the wiper arm simply by pulling it out with your thumb and index finger. Unbolt the 14 mm nut from the driver side wiper and two 14 mm nuts from the passenger side wiper. Set nuts aside and lift wipers out.
Remove the windshield wiper driver side and passenger side end-caps by inserting a Flathead screw driver between the crease and turning clockwise. The end-cap should lift up. Remove and set aside.
Remove two push-pin retainer clips from the windshield wiper cowl, one on the driver side and one at the passenger side. Simple push the the circle on each pin until the pin is released. Remove the push-pin retainer clips and set aside.
Disengage the five clips on the windshield wiper cowl from the windshield motor sub-assembly along the passenger half side of the vehicle. You can do this by simply pinching the clips with a needle nose pliers or pushing them with a Flathead screwdriver until they disengage.
Then I gave it a nice hose down with water.
Disconnect the windshield wiper motor cable by pinching the clip down and pulling out. A pair of needle nose pliers may make this easier.
Disengage the windshield wiper motor cable from the wiper motor assembly at the locations marked in yellow. The clip marked in the red circle is removed once the wiper motor assembly is removed:
Remove four 10 mm bolts from the wiper motor assembly and then lift the wiper motor assembly off from the wiper motor sub-assembly.
Remove three (3) 10 mm bolts from the cowl body mounting reinforcement bracket and remove bracket:
Remove nine (9) 10 mm bolts from the outer cowl top panel sub-assembly on the marked locations and set aside. Clear the plastic cable channels from the chassis then carefully lift the sub-assembly out.
Spark Plug Replacement Instructions
Pop out the plastic cylinder head cover simply by lifting it up, the unbolt four 10 mm bolts from the four ignition coils. Unplug the cable connector from each ignition coil.
Remove all ignition coils by pull it out of their sockets and set aside.
Using your magnetic 9/16 spark plug socket, remove each spark plugs and set aside.
Add a drop of anti-seize grease to the thread of each new spark plug, re-insert them into their cylinders and hand tighten being careful not to over-torque (15 lb-ft if not using anti-seize, 13 lb-ft if using anti-seize). Repeat for the remaining three spark plugs.
As jeffreyd00 pointed out in the comment section, these specific NGK plugs do not need anti-seize lubricant as the threads on the spark plugs themselves are plated with anti-corrosive material. I added anti-seize out of habit and dialed the torque down by 2 lb-ft when torquing.
Re-install the ignition coils and re-connect the ignition coil cables. Replace the engine cover and then re-assemble the motor wiper sub-assembly, assembly and cowl in the reverse order of removal. Enjoy your Prius for another 120,000 miles! I'll write up a DIY guide on replacing the spark plugs from a Prius c once my wife's car reach that point.