I have a 1997 merecedes e320 and it have a

Possible causes
- Warm Up Three Way Catalytic converter deterioration or malfunction
- Exhaust system leaks
- Loose front or rear HO2Ss
- Faulty front heater O2 sensor
- O2 sensors harness is open or shorted
- O2 sensors poor electrical connection
Tech notes
As the code description implies the P0422 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be replaced to fix the problem. If the P0422 code is combined with other codes, try fixing the other codes first.

Here you go!
http://engine-codes.com/p0422.html

Its the sensor telling you to run Terra cleaner!

Section 309-00: Exhaust Components - General Information 1997 Escort, Tracer Workshop Manual REMOVAL AND INSTALLATION Three Way Catalytic Converter (TWC) Removal

1. CAUTION: When servicing the exhaust system or removing exhaust components, disconnect the heated oxygen sensors at the wiring harness to prevent damage to the sensors and harness.
   Disconnect the heated oxygen sensor (HO2S) electrical connectors.

1. Remove the (A) five nuts and remove the (B) exhaust manifold heat shield.

1. Remove the four exhaust manifold to three way catalytic converter (TWC) nuts.

1. Raise and support the vehicle; refer to Section 100-02 .

1. Disconnect the downstream HO2S and position it aside.

1. Remove the two TWC bracket bolts.

1. Remove the two (A) TWC to muffler inlet pipe bolts and nuts and the (B) TWC. Discard the gasket.

P0422 Buick - Catalyst below threshold.

Catalytic converter is clogged or out of medium.

Replace it.


ACTUAL DIAGNOSTIC:

Fault Code Definition
Code P0422 indicates that the Bank 1 Main Catalytic Converter's emissions efficiency has fallen below the minimum allowable limit. This threshold is tracked by a Catalyst Monitoring Oxygen Sensor located on or near the outlet of the Catalytic Converter.

Symptoms

* Check Engine Light will illuminate
* In many cases, no abnormal symptoms may be noticed

Common Problems That Trigger the P0422 Code

* Defective Catalytic Converter
* Engine misfires have damaged the Catalytic Converter
* Internal engine damage resulting in high oil consumption and/or a leaking Head gasket has damaged the Catalytic Converter

Common Misdiagnoses

* Oxygen Sensors are replaced when the real problem is a damaged Catalyst
* Catalyst is replaced when the real problem is internal engine damage, which is producing elevated emissions levels
* Catalyst is replaced when a misfiring engine is the real problem



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P0422 - Catalyst below threshold.

Catalytic converter is clogged or out of medium.

Replace it.


ACTUAL DIAGNOSTIC:

Fault Code Definition
Code P0422 indicates that the Bank 1 Main Catalytic Converter's emissions efficiency has fallen below the minimum allowable limit. This threshold is tracked by a Catalyst Monitoring Oxygen Sensor located on or near the outlet of the Catalytic Converter.

Symptoms

* Check Engine Light will illuminate
* In many cases, no abnormal symptoms may be noticed

Common Problems That Trigger the P0422 Code

* Defective Catalytic Converter
* Engine misfires have damaged the Catalytic Converter
* Internal engine damage resulting in high oil consumption and/or a leaking Head gasket has damaged the Catalytic Converter

Common Misdiagnoses

* Oxygen Sensors are replaced when the real problem is a damaged Catalyst
* Catalyst is replaced when the real problem is internal engine damage, which is producing elevated emissions levels
* Catalyst is replaced when a misfiring engine is the real problem



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• 16706 P0322 Ign./distributor Eng. Speed Inp. Circ No signal
• 16687 P0303 Cyl. 3 Misfire Detected
  
• 16806 P0422 Main Catalyst, Bank 1 Below Threshold

P0322 Could be caused by a faulty Engine Speed Sensor also known as a Crankshaft Pos./Engine Speed Sensor.

P0303 Might have a faulty #3 Fuel Injector, Faulty spark plug and/or faulty spark plug wire and connectors.

P0422 Either your front 02 sensor is faulty and/or your catalytic converter is fried and needs replacing.

P0422 - Catalyst below threshold.

Catalytic converter is clogged or out of medium.

Replace it.


ACTUAL DIAGNOSTIC:

Fault Code Definition
Code P0422 indicates that the Bank 1 Main Catalytic Converter's emissions efficiency has fallen below the minimum allowable limit. This threshold is tracked by a Catalyst Monitoring Oxygen Sensor located on or near the outlet of the Catalytic Converter.

Symptoms

* Check Engine Light will illuminate
* In many cases, no abnormal symptoms may be noticed

Common Problems That Trigger the P0422 Code

* Defective Catalytic Converter
* Engine misfires have damaged the Catalytic Converter
* Internal engine damage resulting in high oil consumption and/or a leaking Head gasket has damaged the Catalytic Converter

Common Misdiagnoses

* Oxygen Sensors are replaced when the real problem is a damaged Catalyst
* Catalyst is replaced when the real problem is internal engine damage, which is producing elevated emissions levels
* Catalyst is replaced when a misfiring engine is the real problem



Thanks for using FixYa - a 4 THUMBS rating is appreciated for answering your FREE question.#$@!

P0422 - Catalyst below threshold.

Catalytic converter is clogged or out of medium.

Replace it.


ACTUAL DIAGNOSTIC:

Fault Code Definition
Code P0422 indicates that the Bank 1 Main Catalytic Converter's emissions efficiency has fallen below the minimum allowable limit. This threshold is tracked by a Catalyst Monitoring Oxygen Sensor located on or near the outlet of the Catalytic Converter.

Symptoms

* Check Engine Light will illuminate
* In many cases, no abnormal symptoms may be noticed

Common Problems That Trigger the P0422 Code

* Defective Catalytic Converter
* Engine misfires have damaged the Catalytic Converter
* Internal engine damage resulting in high oil consumption and/or a leaking Head gasket has damaged the Catalytic Converter

Common Misdiagnoses

* Oxygen Sensors are replaced when the real problem is a damaged Catalyst
* Catalyst is replaced when the real problem is internal engine damage, which is producing elevated emissions levels
* Catalyst is replaced when a misfiring engine is the real problem



Thanks for using FixYa - a 4 THUMBS rating is appreciated for answering your FREE question.!@##

P0422 does not refer directly to an O2 sensor. That is a different code. P0422 is about the CAT. How many miles you have it and when did you buy it? VW has extended a warranty on the New Beetles for the CAT to 120,000 mi and 10 yrs. I had the same code and took it to the dealer to see if they'd replace the CAT in the warranty and they did. I had 47,000 miles and bought it at the end of Aug 1999, so I just slipped through. They replaced the downstream O2 sensor as well - all free of charge!

P0133 is an oxygen sensor "response too slow" code (meaning it's not getting up to temperature quickly enough, and the computer is assuming damage to its heating element). P0422 is a catalytic converter problem indication (cat is below peak efficiency). It's assuming you have a failure with the primary O2 sensor and that the cat is also bad. Change your O2 sensor first, have the codes cleared, and see if the cat code comes back or if the O2 sensor change fixes both issues.