How to replace spark plugs on Generation 2 – 2004 2005 2006 2007 2008 2009 Toyota Prius:
Spark plugs on a Gen 2 Toyota Prius should be changed every 60k to 80k intervals. Some say it should be fine up to 100k to 120k, but it is always a good idea to be cautious. It should be simple and inexpensive, if you have the tools. The NGK Laster Iridium Spark Plugs should cost about $30 online or about $40 at your local auto parts.
Estimated job time is 1 hour to 2 hours.
- 10mm socket
- 5/8 spark plug socket or deep socket – Spark Plug Socket 3/8-Inch Drive by 5/8-Inch
- 4″ Extension – 4″ Socket Extension
- Long nose pliers – Long Needle Nose Pliers
- Spark Plug Gapper (.043 spark plug specification) – Spark Plug Gap Gauge
- Iridium Spark Plugs – Toyota Prius NGK Laser Iridium Spark Plugs (4 Pack)
- Compressed Air Duster – Cleaning Air Duster
- Torque Wrench – Digital Torque Adapter 3/8″ Drive | 147-750 Foot-Pound | Audible Alert
Step 1: Remove the 2 bolts on relay box with the 10mm socket.
Step 2: Disconnect the harness on the ignition coils. This can become difficult but I figured the best way to do it is by prying it from the inside of the harness while at the same time pressing on the lever and pulling it out (example image below).
Step 3: Clean the surface around the ignition coils to make sure no debris falls into the spark plug. You can use compressed air to blow away any debris. Cleaning Air Duster
(Repeat steps 4 to 6 for each spark plug)
Step 4: Remove the 10mm bolt on the ignition coil, pull the ignition coil straight up, and check for signs of wear to judge how the engine is performing.
Step 5: Individually remove spark plug with a 5/8″ spark plug socket or deep socket on a 4″ extension ratchet. It should be around 30 – 35 full spins counterclockwise to loosen. If you don’t have a spark plug socket that holds the plug you can use the long nose pliers to reach and remove the spark plug from the the engine. If spark plugs are hard to loosen you can use a little PB blaster or WD 40.
Step 6: Inspect the spark plug to judge the level of wear and make sure it is normal. Make sure the new spark plug gap is set at the .043 specification. Replace with new spark plugs and if possible new ignition coils too. Torque the spark plugs at 13lbs.
Step 7: Bolt ignition coils, relay box, clean up, and enjoy your Prius.