Here's the procedure from the 2010 Vibe owner's manual (kin to the Matrix/Corolla). Summary: drive a few miles, then check fluid with the engine running in park.
(On my Vibe at least, the handle is not orange as stated. Also, the operation is not "difficult." And, after all the warnings about using the wrong fluid, the manual recommends the wrong fluid. But that's beside the point for your purposes.)
How to Check Automatic Transmission Fluid
This operation can be difficult, you may choose to have this done at the dealer/retailer service department. If you do it yourself, be sure to follow all the instructions here, or you could get a false reading on the dipstick.
Notice: Use of the incorrect automatic transmission fluid may damage your vehicle, and the damages may not be covered by your warranty. Always use the automatic transmission fluid listed in Part D: Recommended Fluids and Lubricants on page 11-18.
Wait at least 30 minutes before checking the transmission fluid level if you have been driving:
• When outside temperatures are above 90°F (32°C).
• At high speed for quite a while.
• In heavy traffic — especially in hot weather.
• While pulling a trailer.
To get the right reading, the fluid should be at normal operating temperature, which is 158°F to 176°F (70°C to 80°C).
Get the vehicle warmed up by driving about 15 miles (24 km) when outside temperatures are above 50°F (10°C). If it is colder than 50°F (10°C), you may have to drive longer.
Checking the Fluid Level
Prepare your vehicle as follows:
1. Park your vehicle on a level place. Keep the engine running.
2. With the parking brake applied, place the shift lever in P (Park).
3. With your foot on the brake pedal, move the shift lever through each gear range, pausing for about three seconds in each range. Then, position the shift lever in P (Park).
4. Let the engine run at idle for three to five minutes.
Then, without shutting off the engine, follow these steps:
The automatic transmission dipstick has an orange handle and is located near the front of the engine compartment.
1. Release the tab and pull out the dipstick and wipe it with a clean rag or paper towel.
2. Push it back in all the way, wait three seconds and then pull it back out again.
3. Check both sides of the dipstick, and read the lower level. The fluid level must be between the two dimples in the hot range.
4. If the fluid level is in the acceptable range, push the dipstick back in all the way; then press the tab down to lock the dipstick in place.