Check engine light flashing, codes P0123 and P0304

Hi Debera,

The check engine light flashing is the most serious type of issue. That means that there is potential catastrophic damage being done to the engine or exhaust. In this case, your issue is the P0304 code. That means that cylinder 4 is misfiring and causing serious damage to the engine or most likely the exhaust because of the raw fuel that is going in the exhaust system due to not being ignited in the cylinder.

I have attached the test procedure to diagnose the P0304. This is the one that you want to address first.

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

The next code is for the throttle position sensor circuit. This needs to be addressed but is not the reason for the flashing check engine light. I have attached this test procedure as well. However, it will depend on which module had this code to determine which test you use. If the code was in the transmission control module, then use the test that addresses the transmission systems. If it was in the engine, then you use the engine specific test.

Please let me know if you have questions or any other info that you need, and I will provide it. Thanks