Dealing with a P0420 code on your Audi can be incredibly frustrating, especially when it keeps returning even after repairs. This error code, indicating “Catalyst System Efficiency Below Threshold Bank 1,” is a common headache for car owners. One Audi owner shared their ongoing battle with this persistent issue, and their experience highlights the challenges and potential solutions for tackling the P0420 code.
Initially, like many, this Audi driver hoped a simple fix would solve the problem. They invested in an oxygen sensor spacer, a common DIY remedy often suggested online. However, this proved to be a temporary band-aid at best. The dreaded check engine light, accompanied by the P0420 code, reappeared after only a month, proving the spacer was not a long-term solution.
Seeking a more permanent fix, the owner opted for a catalytic converter replacement, a repair directly related to the P0420 code. To their dismay, even a new catalytic converter didn’t eliminate the problem. The P0420 code stubbornly returned, leading to further investigation. A diagnostic test at the repair shop, where the catalytic converter was installed, yielded no clear answers, as the emission system appeared to be functioning correctly.
Frustration mounting, the Audi owner took matters into their own hands and purchased an OBD-II code reader. This affordable tool allowed them to clear the P0420 code themselves whenever it appeared. While not a true fix, it offered a convenient way to temporarily silence the check engine light and confirm the recurring issue was indeed still just the P0420 error. For around $33, this code reader became a regular tool in their passenger seat pocket, used to reset the light about once a week.
To explore all avenues, the owner even visited an Audi dealership for a professional diagnosis. Surprisingly, the dealership offered a free diagnostic service and confirmed the catalytic converter as the likely culprit, echoing the previous repair. However, the dealership’s quote for a replacement was double the original cost, leading the owner to decline and continue their search for a more cost-effective solution.
Despite replacing the catalytic converter and exploring other potential causes, the P0420 code persisted. At this point, the owner considered an ECM (Engine Control Module) flash or reprogramming. The theory was that the new catalytic converter might be operating just outside the ECU’s programmed tolerance range, triggering the P0420 code. However, the high cost quoted by the dealership for this ECM service, around $400 for a potentially quick procedure, made them hesitant.
For now, the owner continues to use the code reader as a temporary solution, resetting the P0420 code as needed. This situation underscores the difficulty in resolving P0420 codes, especially in Audis, even after seemingly relevant repairs like catalytic converter replacement. While a code reader offers a quick way to manage the check engine light, it’s not a permanent fix. Further investigation, possibly including ECM adjustments or deeper emission system diagnostics, might be necessary to truly resolve the underlying issue and eliminate the persistent P0420 code on this Audi.
