2012 Prius Spark Plugs Replacement

Damn! That's all my car is worth? I just changed out the spark plugs last weekend on my 2012. I used the NGK as that was the usual recommendation. In and out in a little over an hour total but I had help.

 

Here's my info on the plug spec'd in owners manual:

spark plug: denso SC20HR11 (toyota p/n: 90919-01253) (requires 9/16" socket)
ngk equivalent: NGK ILKAR7B11

I did a quick search on Amazon (US) and see lots of hits. First search result, plus more across top of page:

 

The actual socket size is 14mm which is .2875mm smaller than 9/16". I recommend a magnetic spark plug socket because there is less chance of the socket coming off the extension after you install the spark plug.

 

Not sure if the gen3's have the same kinda mass air flow sensor as the gen2, but if it does id recommend cleaning that also and its pretty easy with the mass air flow cleaner. I did it on my old gen2 and on my gf's gen 2 not that long ago.

 

I installed Denso Iridium TT (Twin Tip) Spark Plugs in my Prius 30,000 km ago. I have a Gen 2 Prius, so I have a different size, but the same type.

You can check the correct part number for your car directly at the Denso site here:
DENSO IRIDIUM TT (at the very bottom)
For your 2012 Prius it confirms part number: IXEH20TT

They come pre-gapped, but because of the thinner electrodes, the gap is purposely set about 0.1 mm smaller than the original Toyota specifications. Mine were pre-gapped between 0.93 and 0.97 mm, and I left them so.

 

Dealership parts department would know.

 

BTW - if you're changing the plugs, here's my story. I have a 2009 Gen II and the plugs were due to be changed at 110,000 so I had the dealer change them during a regular service, and was surprised to get a call from dealer offering to change the PCV (diagnostics said it was needed) for just the price of the valve (~$11), since they were changing the plugs anyway. It is my understanding that it's a rather fiddly job, and requires dissassembly! (FWIW) BTW Welcome to PriusChat! - hope this helps - Wil

 

Also why is SC20HR11 still being recommended? It has been replaced and now the recommended plugs for Gen3 Prius is SC16HR11 (Part #90919-01275).

 

Agree. To be fair, my mention of SC20HR11 was in Feb 2017. Same socket size anyway.

I had a bear of a time even finding 9/16" locally. 5/8' was usually the smallest most automotive places had. Ended up getting a 4 size made-in-China set through Princess Auto for around $20 CDN. A check now on Amazon I see it's no problem finding 14 mm though.

And yeah, 9/16" is 14.2875 mm.

 

Ouch!.. I didn't realized this was an old thread. Yes the Toyota made the change sometime in 2017 as I recall.
So Mendel, you were right recommended the 20HR11 at that time. I didn't pay attention to the posting date. Now it is SC16HR11. But both will work for sure

 

I am also wondering about this new Iridium TT sparkplugs. What I found that some of the newest Toyota with dual injectors D4S are using Iridium TT as the OEM/Genuine original Toyota Parts. There is indeed some improvement on Iridium TT over older Iridium. Both has the same ground electrodes made out of Platinum, not Iridium. Only the main tip is Iridium.

 

If I remember right, the main difference is that the stock plug has a 0.7 mm iridium needle pointed at a platinum ground pad, and the TT has a finer 0.4 mm iridium needle pointed at a 0.7 mm platinum ground needle.

The thicker needle on the stock plug will last longer. The thinner needle on the TT will require a lower secondary voltage to form a spark, which could be advantageous if your engine condition and driving conditions are such that the stock plug is borderline at doing its job.

The ECM has some pretty sensitive measurements to show you how your current plugs are doing. For starters, there are the misfire counts, accessible by viewing the misfire monitor. If those are staying at 0 for all cylinders, your current plugs are getting the job done. But beyond that, there is a metric called the misfire margin (at least starting in Gen 3; I don't know if Gen 2 tracked this). This number can be negative (misfires are happening) or positive (if less than 30, at risk for misfiring; higher than 30, not really at risk, higher is better). Last time I checked mine it was something like 134.

If you have looked at your misfire margin and it is some very comfortably high number like that, the odds are pretty much nil that any change to any kind of better plug is going to change anything. The plugs only do one thing and a sky-high misfire margin shows they're already doing it way better than they need to. (That doesn't mean, given that we're human, you couldn't change to fancy plugs and convince yourself you feel wonderful things happening.)

If your current misfire margin is lower, getting down near 30 or worse, then it is possible a change of plugs could improve something. But it would also be worth investigating whether anything else is going on with the engine that could be contributing to the low margin.

 

It turns out I spread some misinformation here about the misfire margin. It is a number the ECM is constantly recomputing while the engine is running, and its normal range tops out at 100. Whenever the engine is not running, this PID sits pegged at 127 (which is normally not a valid value for it). So it's no use to just go ask "what's my misfire margin?" and get a single number, which'll just be 127 if you're asking when the engine is stopped. It doesn't somehow summarize the whole drive you just made.

It is more useful to datalog and graph the misfire margin, over a short drive that takes in various driving conditions. If you're using Techstream, you can graph several things at once, like coolant temperature, RPM, engine load, EGR %, and misfire margin, and look for where the margin gets lowest, and what the other engine conditions were at that time.

For what it's worth, misfire margin wasn't new for Gen 3; I checked in the Gen 2 repair manual and it's in the Gen 2 data list also.