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P0422 Fault in 1997 VW Jetta with 130k Miles - O2 Sensors and Catalytic Converter Diagnosis

Model: 97 vw jettas Fault Code: P0422 Posted: 2008-05-02 16:41

I recently purchased a 1997 VW Jetta with 130,000 miles. The vehicle runs smoothly, but the Check Engine Light is on and I've been reading a P0422 diagnostic code. I've already replaced the oxygen sensors (including downstream O2), spark plugs, plug wires, intake gasket, cap, and rotor—all using Bosch OEM parts. I’ve heard criticism about Bosch O2 sensors being low quality, but they are actually the original equipment manufacturer (OEM) for VW and Audi, and are used in over 75% of vehicles built. The car shows no noticeable symptoms: no smell from the exhaust, and no rattling or noise when tapping on the catalytic converter. I recently broke the crankcase breather tube, but I don’t believe this is related to the P0422 code. My question is: what could be causing this code? Is it possible that the catalytic converter itself has failed internally, even without visible symptoms? Given the high mileage and age of the vehicle, should I consider replacing the catalytic converter or are there other potential causes?

Related fault codes
P0422
Comments (7)
Anonymous 2008-05-03 06:13

The absence of a smell or rattling noise does not rule out internal catalytic converter failure. Many vehicles with high mileage show no external signs before failing.

Anonymous 2008-05-04 00:03

For high-mileage VWs, especially over 100k miles, it's common for the catalytic converter to fail internally. Replacing the catalytic converter is often necessary in such cases.

Anonymous 2008-05-04 12:25

As a technician at a VW dealership, I've found that over 90% of P0422 issues in high-mileage vehicles are due to internal catalytic converter failure. Often, the downstream O2 sensor is also faulty. Replacing both components and performing a dealer-level reset of the readiness codes is typically required. While catalytic converters are expensive, aftermarket units often don't perform as well or meet emissions standards. Bosch O2 sensors are not defective—they are OEM parts used in millions of vehicles worldwide.

Anonymous 2008-05-05 12:41

I fully agree with the Bosch O2 sensor claims. In my experience, Bosch parts are high quality and reliable, especially when correctly matched to the vehicle model and year.

Anonymous 2008-05-09 05:06

100% agree—Bosch sensors are not inferior. If they were truly problematic, why would they be used as OEM components in such a vast number of vehicles and commercial trucks?

Anonymous 2008-05-09 05:25

My experience suggests that the issue may stem from incorrect part selection rather than poor quality. For example, getting the wrong Bosch O2 sensor model (e.g., wrong zone or type) can cause incompatibility. The best practice is to match the replacement part with the original using part numbers or consult a dealership technician who knows the OEM specifications. This issue has been discussed online—especially among Toyota owners who sometimes receive incompatible sensors from aftermarket suppliers. I always recommend verifying compatibility before installation, as even high-quality parts can fail if misapplied.

Anonymous 2008-05-09 17:25

Exactly—the correct part is essential. Even the best-fitting wrong part will not function properly and may lead to persistent diagnostic errors or engine performance issues.