i have a check engine light on and checked the codes today, i have 3 being thrown.
1. p0128- i am guessing a new t-stat is all thats needed.
i searched some of the previous threads about the 420/430 codes and am still a little concerned about how to properly diagnose which and how many of the four O2 sensors need replaced (if thats what i should be doing).
any ideas if the combination of the 3 codes together should tell me something? the 4 cyl. HL has 108k on it, i have noticed reduced fuel milage, i used to get about 24mpg in town and 27-28 highway. now i get about 18 mpg in town and lucky to get 21 highway. it has orignal O2 sensors, any suggestions???