Hello, Mike. Typically, there would be a warning light on the dash. However, it is always a good idea to have an OBD II reader. The only warnings I have seen, so far, have been a shifter warning that is always due to an older 12V battery that needs to be replaced. If you do buy an OBD II reader, you should get one that is capable of reading Toyota/Lexus codes.
Here's one possibility, although it'd be prudent to query the seller about the reader's compatibility with your vehicle.
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