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Q: Check Engine light on

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I brought my car for inspection and it failed due to the check engine light. It's showing a P0740 and P1456 codes. I went to my regular mechanic and said that I need to replace my transmission! About a month ago, I was there for an oil change and a transmission fluid replaced. My maintenance required went off but then the check engine light went on? I'm asking for a second opinion. Thanks!

My car has 218183 miles.
My car has an automatic transmission.

Fault code P0740 has to to with the evaporative system. It can be as simple as a loose fitting or sealing gas cap. It can also be more involved to include the purge valve and/or bypass solenoid. When you add fuel to the tank, the fumes need to be vented or the tank will not fill. The fumes are routed through valves and hoses into the charcoal canister. They are stored there until the engine is running. Then the system sends the fumes forward to the engine to be burned away. If this system is not tight (pressurized), then this fault can be set. Code P1456 has to do with torque converter lock-up. The torque converter is what connects the engine to the transmission to transmit power to the wheels. At certain speeds, the torque converter will "lock up" - create a 1 to 1 connection with the engine and transmission for maximum efficiency. If this lock up is not occurring, this code will be set. It may very well require a transmission replacement. Replacing the transmission fluid neither caused this not would have prevented it from happening. You can try replacing the gas cap with a genuine replacement but I would have a local transmission specialist inspect the transmission to determine if there is an alternative to replacing it.

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