Replacing Underbody Panels

As I recall, Toyota uses 7mm nylon plastic push in rivets. M5 rivet nuts fit this hole perfectly without enlargement.

If you prefer to enlarge the holes, they can take M6 rivet nuts and M6 flange bolts.

To prevent the holes from tearing through the polyethylene plastic, I recommend and personally use large 1/4 inch fender washers with neoprene linings, which I purchased off of Amazon.

 

More stainless steel neoprene fender washer alternatives that will fit M6 fasteners.

 

Looks sim to 3rd gen. It "looks" like it could be two pieces, and the arched bit and flat back bit likely could be separated, when new. 3rd gen has a slim flat-bar piece at the junction, and 3 bolts going into tack-welded nuts on the flat-bar, at the junction. When I tried to back out those bolts with our 2010, a few years past new, I snapped the heads off (twice, then gave up). The bolts/nut junctions looked like they'd been at the bottom of the sea for a while.

Oh and on 3rd gen, there was one fastener at the very rear that pretty much has to be destroyed to remove.

 

It ships folded up IIRC, fairly thin material. Start a check-out process and see what it amounts to, to know for sure. If you bail they’ll likely send you an (automated) email, saying “did you forget something?”, no big deal. Research the fasteners too (for any MIA); I’d go with the Toyota, just my 2 cents.

if you do order fasteners, remove the damaged one first, to make completely sure which you’ll need: again, there’s one that may need to be destroyed to get off.

 

What did you end up doing? I’m in the same boat. About $85 shipped for the whole assembly (The cost is no biggie, so hate to buy and ship more plastic I don’t need), when I just need the triangular part—which is clearly a separate piece since I have it in front of me.

The main problem is that one of the corner pieces tore (see photo) and I’m not sure I can re-fasten it in a way it will stay on. I’m wondering if there is a set of washers with “teeth” that I can use to re-attach this corner.

 

Get rid of the small piece that broke off and use these #14 x 1" Neoprene EPDM Bonded Sealing Washers, Stainless Steel.

For additional stability, one can bond the neoprene portion to the contact point of the undercover with a high strength contact cement, epoxy or 3M VHB tape.

I use them to prevent the little piece from breaking off in the first place, The neoprene washer spreads the contact over a larger surface area.

 

I would first put that broken off piece back in position, with 2-part epoxy in the joint, and beyond. Let that cure, then sandwich the area with a folded-over piece of fiberglass mesh (designed for bridging gaps, strengthening), covering the whole area, including and beyond the hole, and apply more 2-part epoxy.

When fully cured, drill a hole through the patch, at the original location and diameter. Maybe start with a 1/8" pilot hole, then (if possible) forstener bit drill from both sides with a drill press.

 

Same issue here Splash guard / underbody panel? | PriusChat
might want to pool resources

 

If it’s just that corner, there are videos in YouTube that show how to weld/solder with a very cheap soldering gun and some plastic scrape and cheap mesh. Most epoxies I’ve tried are still too weak and are prone for breakage again.

 

Yes, I actually came across soldering for plastic repair which I had not thought of. I have a 4hr drive today and don’t have my soldering gun with me, but will give that a shot when I’m home. For the drive today, hopefully the fender washers I was able to get locally (not as large as I’d like) will hold well enough (seems like it should be good enough for one trip).

It seems we also lost two of the three plastic clips, so I’ll need to check this and a couple other threads for replacement options (I think I saw a couple mentioned).

 

If you pull the clips you're missing from the other side of the car and post a picture with a dime or quarter next to them, someone will find the right part number for you.

 

Or just check for yurself. Even the best parts sites can be a little frustrating, but it's all there. The more you use them the easier it gets.

Some good ones:

Toyota Parts and Accessories - Official Online Store

https://toyotaparts.mcgeorgetoyota.com/

Genuine Japanese Car Part Imports - Amayama

 

I actually found that:

Genuine OEM Toyota Parts and Accessories Online - Toyota Parts Deal

Has good prices and much more reasonable shipping costs on larger parts than I found on McGeorge (who I have used before). Pretty sure I know which plastic clips I need, but pay try to use something a bit more durable, especially since I think at least one of the two holes stripped a bit when they were ripped out.

 

A tip for plastic fasteners, typically the ones with the centers you need to pry up: ALWAYS wash them out with hot soapy water when they've been removed, and work the mechanism back/forth a bit. And be careful installing them: be sure all the little jaws are squeezed together, go into the hole.

A paint can opener tool is handy for prying them out:

 

I hate those plastic attachments manufacturers use because there's so many different types and sizes. I have a bunch of boxes of various sizes I got off Amazon in my garage and have to search through them to find one that will fit those that are missing or damaged when working on vehicles. And, in the rare instance where I can't get one to fit, a zip-tie is my last resort. (But that's pretty rare, I'm getting pretty good at preserving the old ones when taking them off.)