How to Replace the Spark Plugs
2004-2009 Toyota Prius
The spark plugs are supposed to last 120,000 miles but I replaced mine a few thousand miles after I rolled over 100k on both of our Prii. It's a pretty simple job that can be done a couple of different ways. I first did this job on our 2008 without removing the air filter assembly by using angled socket joints and various socket extensions. It works but isn't what I'd recommend. The method shown here is much less frustrating and gave me far better access. Although there is more to remove here it really doesn't take that long. You can combine this with other jobs like PCV valve replacement, MAF cleaning and/or throttle body cleaning.
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Tools Needed:
- Socket wrench set
- Socket extensions
- 16mm spark plug socket
- Torque wrench (20-200 in-lbs)
- Torque wrench (10-80 ft-lbs)
Parts/Supplies Needed:
1) Follow steps 1-3 to remove the relay block, air filter assembly and undo wiring harnesses. The fuel injector wiring harnesses do not need to be removed unless you're also replacing your PCV valve.
2) Remove the 4 10mm bolts circled in red, 80 in-lb (9.0 Nm, 92 kg-cm).
3) To reduce the chances of dropping something into the spark plug holes I would recommend replacing the plugs one at a time. Remove an ignition coil. It may help to rotate it a bit.
4a) Remove spark plug using a 16mm spark plug socket. You'll have to figure what extensions work for you depending on the tools you have. I used two shorter socket extensions along with the spark plug socket as shown. Tape it up if you're worried about this falling apart. I then fed that into the spark plug hole and aligned it on the spark plug. Next I put the socket wrench on and removed the plug.
4b) Put some dielectric grease on top of the new plug, then place it in the spark plug socket. Now apply anti-seize to the threads as shown.
5) Using your extensions and spark plug socket from step 4 carefully feed the new plug into the spark plug hole and then thread it by hand with the socket extension(s) to avoid cross-threading. Once it's hand tight torque to 13 ft-lb (18 Nm, 184 kg-cm).
6) Install the ignition coil and torque the 10mm bolt to 80 in-lb (9.0 Nm, 92 kg-cm).
7) Repeat steps 3-6 for the remaining 3 spark plugs.
8) Assembly is reverse of removal.
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