Nothing to do with the thermostat. The QUAD driver monitors various sensor circuit but when code 26 or 27 comes on, it means any one of these could be the cause. The QUAD driver does not know which circuit has failed.
For such testings, a scan tester would be recommended as it allows you to monitor each circuit and see if any is not within specs. If you keep changing parts and hoping that it solves the problem, it could be costly and a waste of time as well.
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Tuesday, June 4th, 2013 AT 7:12 AM