Service engine soon/ABS/Trac lights are staying on

Have the ABS codes scanned. This will get you started in the right direction. Possibility is that one or more of the wheel speed sensors is not working or intermittent - could be wiring or connectors on these as well. Another possibility is the EBCM, Electronic Brake Control Module. I believe the EBCM will throw 1216 code in many cases. THese can be rebuilt online for about $150.00.
The more likely problem is the wheel speed sensors. THese are an integral part of the wheel hub. About $100.00 each for the part. About $250.00 each to have them replaced. They can be tested with an AC voltmeter by spinning the wheel. Also, they should read roughly 850 ohms resistance. The ABS codes will tell you which ones are not reporting.