Hello All, I know there have been previous threads with the said error code "P0303" however, I wanted to post a thread with more clarity with actual results. 1 day ago while driving I came to a red light, once stop I noticed my CEL flashing with the display warning showing Check Emissions System also noticed the error code P0303. Also the car was noticeably sputtering with an engine shake. I didn't want to turn the vehicle off due to not knowing what the actual issue was. On the drive home while coming to red lights the RPMs dipped very low almost seeming to cause the car to shut off. I made it home, was able to turn the vehicle off & start it up again. After restarting the car I noticed more indicators showed, the Check SH AWD system, VSA error, & the code 77. After reading threads on here I determined the other indicators came on due to the original error code P0303. I bought 6 new NGK Iridium Spark plugs & replaced the old ones. No oil in the spark plug cylinder for all 6 which is a good sign. After starting the car up after the plugs were replaced I noticed the sputter sound (coming from rear exhaust), as well as the slight engine shake was still present. Going back to the error code P0303 for cylinder 3 & determining the firing order, I replaced the coil pack for cylinder 3. The sputter sound & engine shake were gone. To save yourselves time & money, replace the spark plugs along with the coil pack. I plan on ordering new coil packs for the remaining cylinders to prevent future failure. Sorry for the lengthy post, just wanted to be descriptive as possible. (2009 TL SH-AWD 3.7L)

Firing Order for Cylinders below:

Firewall
1 2 3
4 5 6
Front of Car

 

Thanks. I’m just wondering if you locked the code up. That might have saved you some time and effort

 

Having the exact problem. Thanks for the detailed description. Will see if mine is fixed similarly.