p0420
Moderate
Porsche · Sedans & Sports Cars
Catalyst System Efficiency Below Threshold Bank 1
Quick Answer
Error code P0420 on your Porsche Sedans & Sports Cars means: Catalyst System Efficiency Below Threshold Bank 1. This is usually fixable — see the step-by-step guide below.
Affected Models
Likely Causes
  1. Faulty oxygen sensor (O2 sensor) downstream of catalyst
  2. Leaking catalytic converter or damaged catalyst substrate
  3. Exhaust leak before the catalyst
  4. Engine running rich due to fuel pressure regulator or fuel injector issues
  5. Failed catalytic converter substrate
How to Fix It
1
Scan for pending codes and read freeze frame data
2
Inspect exhaust system for leaks before the catalyst
3
Test upstream and downstream O2 sensors with a scope
4
Measure catalytic converter temperature and efficiency
5
Replace catalytic converter if efficiency is below specification
Pro Tip
This fix requires some technical knowledge. If you're unsure about any step, consider contacting support or a qualified technician.
Parts You May Need
Catalytic converter assembly
Oxygen sensors (upstream and downstream)
Exhaust gaskets
Heat shielding
Related Error Codes
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