A part fell off my Prius. Trying to identify...

That's an exhaust heat shield. Avoid parking in tall dry grass lest you start a grass fire.

 

Good one IM. That's a guaranteed fire.

A complete and thorough inspection of the undercarriage is in order. You'll start dropping off exhaust parts next.

 

i thought it was a rusted out bedpan. welcome to priuschat!

 

Heat shield - good eye ... not to be confused with the nearly identical and often misidentified 'Sfetzer' valve.

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INSULATOR - 17168-21030 | Buy Genuine Parts at Mid Atlantic Toyota Parts

 

The same part just fell off my 2005 Prius. The picture above shows that it's the exhaust manifold heat shield. But the diagram in the attached link to Mid Atlantic Toyota Parts looks like a different part.

Did you have the part replaced. Was it expensive? Thanks!

 

Apparently, the area around the mounting bolts rusted but. The material is probably 409 stainless steel, which is very rust resistant at room temperature; NOT so much at elevated exhaust manifold temperatures.

 

The heat shield was above your exhaust, not below, so don't worry about grass; replace the donut at the junction of the header and exhaust pipe, it's toast if the shield is, and the tailpipe is likely.

 

#3 is the larger sheet metal part that covers the exhaust manifold while #4 is the smaller part that shields a portion of the exhaust pipe near the air/fuel ratio sensor and is the part that fell off. I agree that the parts catalog appears to have a typo.

 

Thanks FGLC and PW! The large heat shield (not shown in the above pictures) covers the top of the manifold. The small one that fell off of our cars faces down. You can tell by the curve of the pipes that it's on the underside of the manifold. (The manifolds in the above photos are lying downside facing up.) That's probably why it rusted. It was more exposed to road salt. I couldn't find a picture of the underside of the car. So I don't know what is below the manifold that needs to be shielded. I doubt if it's wires or anything highly heat sensitive. But I'm not sure. It might be suspension and steering components. Maybe I'll have the car put up on a lift and look for myself.

Does anyone know what the heat shield below the manifold is protecting? How essential is it to replace the shield? It's too high in the engine compartment to touch grass and start a fire. But there must be something under the manifold that needs protecting. Otherwise there would be no shield.