I'm trying the TPMS relearn for the first time, using an OEC-T5 EL-50448 relearn tool (recommended elsewhere on this forum). Following the process in the 2017 Volt manual, I successfully relearn the first 3 tires, as indicated by a horn beep, but the fourth (driver-side rear) tire fails to relearn. I leave the tool on for up to 3 minutes on the last tire, still within the 5-minute limit for all 4 tires, but it doesn't take. I tried moving the relearn tool around some along the sidewall in the area of the valve - no luck. Sometimes the other 3 tires take up to about a minute to relearn, but they always work. Could this be a bad TPMS unit in that tire? Anyone else have this problem? Tricks I could try?