My check engine light was throwing the code P1121 for the coolant flow valve. Toyota replaced it under a warranty enhancement (I have 134k on it), and since then my mpgs have gone from 46 to 50. My AC is working much better now, too. My theory is that the valve can be in a semi-failure mode for a long time before throwing a code. Now that My coolant is flowing the way that it should, heat is being disappated more efficiently. Any thoughts or anyone with a similar experience?
Coolant flow valve. Part 16670-21010. The check engine code was P1121. Under warranty until 150k at least here in CA.
The impact of a failed engine coolant flow valve would include: 1. The cabin heater may not function very well 2. The engine may take slightly more time to reach operating temperature since the coolant heat recovery system would not be functioning. I would not have expected a failed valve would impact mpg as much as you have noticed. Perhaps some other factor is contributing to the improved results.
