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2005 Chevy Cobalt LT - Fault Codes P0300 and P0455: Causes and Fixes

Model: 2005 Chevy Cobalt LT Fault Code: P0300 Posted: 2019-01-04 15:23

In mid-2018, my 2005 Chevy Cobalt LT developed a gas line leak that was repaired. Since then, the vehicle has exhibited unusual behavior. My brother used his OBD2 scanner and found two diagnostic trouble codes: P0300 (random misfire) and P0455 (large evaporative emission system leak). I'm seeking advice on what these codes indicate and what repairs are necessary to resolve them. Any insights or experiences with similar issues on this model would be greatly appreciated.

Related fault codes

P0300P0455

Comments (4)

Anonymous 2019-01-05 14:59

P0455 indicates a significant EVAP system leak. Start by checking the gas cap—this is often the root cause. Once confirmed, perform a purge cycle to reset the system and verify if the code clears.

Anonymous 2019-01-05 21:29

I recently resolved my P0300 issue, but yesterday the car unexpectedly shut off while braking twice. This behavior is concerning—could it be related to ignition or sensor problems? Any thoughts on possible causes?

Anonymous 2019-01-06 08:07

What specific action was taken to fix the P0300 code? And what steps have been taken to address the P0455 issue so far?

Anonymous 2019-01-06 15:58

For the P0300, we replaced both the ignition coil and the ignition control module. For P0455, no action has been taken yet—however, the dashboard consistently displays 'CHECK GAS CAP,' which suggests a faulty or loose cap. I plan to replace it as a next step.