← Back to list

2006 Chevrolet Cobalt 2.2L with P0128 and P0420 Codes: Smog Passed Without Check Engine Light

Model: Chevy Cobalt Fault Code: P0128 Posted: 2016-06-30 15:10

I recently passed my smog inspection on my 2006 Chevrolet Cobalt with a 2.2L engine, but two diagnostic trouble codes—P0128 and P0420—are still active. Notably, the check engine light is not illuminated. Could the Engine Control Module (ECM) be responsible for both of these codes? Or are they stored in memory or history rather than being actively triggering a warning?

Related fault codes

P0128P0420

Comments (2)

Anonymous 2016-06-30 16:08

This situation seems inconsistent—passing smog with two active DTCs (Diagnostic Trouble Codes) and no check engine light is unusual. Typically, emission tests require the check engine light to be on or triggered during the test process. It's possible that P0128 and P0420 are either pending or stored in the vehicle's memory/history rather than being actively active. Does the catalytic converter monitor show it's 'ready'?

Anonymous 2016-06-30 16:16

All emission monitors have been completed successfully during the smog test. The P0128 code may be pending, and P0420 could be in history mode. Since I passed the inspection, I'm considering clearing these codes to see if they reappear under normal driving conditions—this would help confirm whether they are truly active or just stored.