Rick's Free Auto Repair Advice

P0420 OBD2 code – Catalytic converter VW or Audi

Fix code P0420 OBD2 code – Catalytic converter VW or Audi

Shops are reporting a rash of P0420 OBD2 code – Catalytic converter VW or Audi. The P0420 OBD2 code indicates that the catalytic converter has an Efficiency Below Threshold (Bank 1). To understand more about P0420 OBD2 code in general and what can cause it, read this article

P0420 Catalytic Converter

But if you own one of the following vehicles, follow this procedure to fix the problem:

2000 Volkswagen Jetta GLS 2.0L
2001 Audi A6 Quattro 4.2L; Beetle 2.0L; Jetta GL 2.0L, GLS 1.8L Turbo, GLS 2.0L, GLX 2.8L; Passat 1.8L, 2.8L
2002 A6 Quattro 3.0L; Beetle 2.0L; Cabrio 2.0L; Jetta GLS 2.0L; Passat 1.8L Turbo, 4 Motion 2.8L
2003 Beetle 1.8L, 2.0L; Jetta GL 2.0L, GLS 2.0L, GLS 2.8L, GLS Wagon 1.8L; Passat 1.8L Turbo
2004 Golf 2.0L, Jetta 1.8L, Jetta GLS 2.0L
2005 A4 Quattro 1.8L Turbo, Beetle 2.0L, Golf GTI 1.8L Turbo
2005-’06 Jetta 2.5 2.5L

On these particular vehicles the P0420 OBD2 code may be the sign of a failed catalytic converter. However, you should not automatically assume the converter is bad. If the vehicle shows any other trouble codes in addition to the P0420 code, deal with those first. Shops report that forcing a readiness monitor update may solve the problem. Forcing the readiness monitors also checks the oxygen sensors and secondary air systems and that may disclose a problem in those devices. This must be done with a factory scan tool. Here’s how:

Overheated catalytic converter

Overheated catalytic converter

1. Clear the fault code
2. Force the readiness monitors on the vehicle.
3. Drive the vehicle. If the P0420 doesn’t return, you’re done.
4. If the code returns a second time, then replace the CAT.

If you replace the cat converter, you MUST replace it with a unit that has the same dimensions as the original. A converter that’s too large or too small with affect airflow and engine performance.

A good catalytic converter should show a 150° difference between the inlet and outlet temperatures, with outlet always hotter than the inlet

Posted on by Rick Muscoplat


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