Check Engine due to Rock hitting underside?

I think the check engine light was your Prius calling out for mercy.

Prii were not designed as an off road vehicle.

Straighten up bub . . . or we will be forced to come rescue your car from being tortured like that.

And speaking of straightening up . . . you may want to consider having an alignment done real soon.

 

You may have pulled loose a connection to the emmissions equipment or broken a wire. I know that the secondary O2 sensor on the cat. converter would give similar indications if it was damaged.

 

I've done a lot of 4x4ing myself.

there's only 1 thing i would be rather worried about while going on the 4x4 roads. if the car ever bottoms out, you risk cracking the casing that runs the high voltage lines. it's a plastic sleeve that runs parallel to the car's main body panels. It's pretty safe, but i would imagine it would cause major problems if it were to ever be hit and started to ground out in any form.

Other than that.. I've never seen any error lights in these situations. I have had rocks get jammed in the engines control arm.. which makes the engine really really rough because the arm no longer dampens do to rocks being in it's travel path.

oh yeah... another thing to watch out for when 4x4.. bending your rear plate (bt tech or stock) it's very easy.. as I've destroyed a bt plate already.

 

It could have been coincidental and not have any thing to do with the rock strike. If you are close to a 5000 mile oil change warning it the light will come on for a time and then go away.

 

Do you know what the code was? That would help a lot rather than just guessing what could have happened.

If you had an older vehicle with a rusty exhaust and no OBDII, I'd venture to say you cracked the exhaust, opened up a gap at one of the joints, put a dent in the exhaust somewhere, or yanked some wires out somewhere.

If the light comes on again, make sure to get the codes scanned.

 

This happened to me recently. Strangely, it was shortly after an oil change.
The explanation was that i must have hit a rock that broke the headlight auto leveling sensor. I checked it out with two different dealerships and did some searching here. It seemed legit. It cost about $350 to have fixed.
good luck