Check Engine Light

I've got a 2003 CVPI that has me stumped. I washed the engine when I bought it it and shorted three coils. It kept showing #1 cylinder misfire after replacing all 8 coils.I swapped the #1 coil with another new one and it still threw the code. I reset the codes and the light didn't light up again for around 500 miles. I ignored it since there were no driveability problems and the gas mileage stayed in the 18-21 mpg range.

Last week it overheated and went into limp home mode. I got it home, refilled the radiator, and let it sit over night and took it to the shop the next morning. I drove it hard and it ran like a new one. The codes they got to show up were catalyst. They drove it and it performed flawlessly. We decided that the thermostat was sticking and changed it. About 500 miles later here comes the check engine light.

It runs smoothly, good acceleration, no heating issues, and got 21 mpg on the last tank. Is this a bad sensor?

Did you pull any codes from when the engine light came on? The engine codes help to track down what system in the circuit is causing the codes. The local AutoZone, O'Reilly's, or Advanced Auto will pull those codes for free. Then you can research the codes online.

Just don't go out buying parts "thinking" what may be wrong. A code for a bad O2 sensor may only mean you have a vacuum leak in that circuit. Hey, I saved some $85 researching the problem online since AutoZone told me it was a bad O2 sensor and I leaned it was a vacuum leak.

Actron makes inexpensive code readers, starting about $39.99. And with the more modern vehicles, you have to have one to do any troubleshooting. Without knowing what to look for can get real expensive.

One of my neighbors replaced fuel pump, fuel lines, fuel filter, injectors, fuel rail, fuel regulator, and oil pressure sensor for the fuel system, only to find out he had a bad short in the coil circuit. The pigtail cost him $6.95 AFTER he had spent over $800 on replacement parts and installed them.