I bought a 2008 Chevy Colorado back in December of 2018 and the Tire Pressure Light had been on since I bought it.  It does not flash.  Also there is a LOW TIRE message on the DIC.  I bought an AUTEL TS601 in hopes that I could diagnose this problem.  The tires on my truck are FALKEN WILDPEAK A/T AT3W 31X10.50R15LT 109S LOAD RANGE C.  These are slightly larger in circumference than the P235/75R15 recommended on the tire placard.

I used my TS601 to activate each of the sensors and they all checked out.  I have attached the report.  I then hooked it up to the TS601 to the DLC with the OBD II cable and performed the TPMS Diagnosis. Their were no fault codes. Then I chose Live Data option and discovered the problem, I think.  The tire pressures shown did not match what the sensors were reading.  I have all my tires inflated to about 40 psi and that is what the sensors are reading.  The tire pressures shown on the Live Data were LF = 19.9, RF = 20.3, RR = 20.3, LR = 57.9. 

 ANY IDEAS???