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Hal, Chevy Master Tech
Category: Chevy
Satisfied Customers: 1031
Experience:  ASE and Chevy Master , 31yr Dealership exp,
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Just changed a coil pack on my 2003 Chevy Silverado vortec

Resolved Question:

Just changed a coil pack on my 2003 Chevy Silverado vortec 5.3L engine and now the service engine light in on. Did it drop a code just because I changed something electrical and it just needs to be reset and is nothing major?
Submitted: 7 years ago.
Category: Chevy
Expert:  Hal replied 7 years ago.

Hi my name isXXXXX to just answer.


Just changing the coil should not have set a code. or need reseting unless the light was on before you changed the coil. A code scanner is needed to check and clear trouble codes on this vehicle.

I would need to know what code is stored to be able to tell you how to repair it.

It could be as simple as a connector not getting plugged back in.

Go over all the wire connectors and make sure they are all seated properly.

The light may take two or three drive cycles before it turns off, if you do find a connector disconnected.

If you find out what code has set let me know and I will help you diagnose it.


Thank you


Customer: replied 7 years ago.

The light wasn't on before I changed the coil pack. I even unplugged the red cable on my battery and left it off for about 5 mins and it didn't reset. I plugged the spark plug wire back in and the plug into the coil pack. Should I unplug the wires and reconnect them with the battery disconnected?

Expert:  Hal replied 7 years ago.

These don't reset by disconnecting the battery. A code scanner is the only way to clear them. If the concern is no longer there for two consecutive drive cycles, then the lamp will turn off.

It is best to have someone see what code is set. If it was missing then it will be a P0300 or P03xx for the cylinder that the coil was replaced for( P0301-P0308)

OBD 2 vehicles are not capable like the OBD 1 vehicles were to reset with disconnecting the battery.

If you need more information, let me know



Hal and other Chevy Specialists are ready to help you
Customer: replied 7 years ago.
The engine is missing on cylinders on 3,5,7 and I changed the one for 5. I planned on getting a code reader on it tomorrow but was just seeing if there was anything I could possibly do to get it fixed tonight. The engine light being on bothers me. Thanks for your help!!