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P0422 OBD-II Trouble Code: Main Catalyst Efficiency Below Threshold

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P0422 code definition

The P0422 trouble code detects that the efficiency of the main catalyst in the first bank is below the standard threshold.

What the P0422 code means

The P0422 trouble code is a generic OBD-II trouble code. The P0422 code suggests that the catalyst efficiency is below the normal threshold in the first engine bank, which is generally the bank that houses the number one cylinder. The efficiency of the catalyst is determined by the powertrain control module (PCM), which uses exhaust and temperature information from both the upstream and downstream oxygen sensors to decide on the efficiency. When the readings from both sensors are determined by the PCM to be too similar, then the efficiency of the catalyst is likely below threshold, and the P0422 trouble code will be triggered.

What causes the P0422 code?

The most common cause for the P0422 trouble code is a malfunctioning catalytic converter. However, there are a many other issues that can result in the code (or that may cause the catalytic converter to malfunction), including the following:

What are the symptoms of the P0422 code?

The P0422 trouble code will usually result in the check engine soon warning light illuminating on the dashboard. It is common for there to be no noticeable symptoms with the vehicle (other than the trouble code and the warning light), but it is also common for the vehicle to have diminished engine performance, a hissing noise and hesitation when the throttle is engaged, and an engine that stalls or will not start.

How does a mechanic diagnose the P0422 code?

The P0422 trouble code will be diagnosed using a standard OBD-II trouble code scanner. A trained mechanic will use the trouble code scanner to assess the P0422 code and search for additional trouble codes. Following this, the technician will reset the trouble codes and restart the vehicle. If the code does not return, it was likely falsely triggered, and there is no issue.

If the P0422 code (and any accompanying trouble codes) returns, the mechanic will inspect all of the wiring and connectors near the catalytic converter. If any are loose or damaged, they should be replaced, and the codes should be reset to see if the issue is resolved. After the wires and connectors, a technician should inspect the catalytic converter itself, and should also search for leaks in the exhaust system.

If an issue is noted with the catalytic converter, the mechanic will inspect other areas of the vehicle to try and find the cause of the catalytic converter damage, as they are usually the result of an issue elsewhere in the engine.

Common mistakes when diagnosing the P0422 code

The most common mistake made when diagnosing the P0422 code comes from not properly following the OBD-II trouble code diagnosis protocol. Failure to follow the protocol may result in replacing the catalytic converter without addressing the issue that is causing the converter to fail, or failure to address other present trouble codes.

It is also common for oxygen sensors to be replaced erroneously. While an oxygen sensor could be part of the issue triggering the P0422 code, it is unlikely to be the primary problem. Oxygen sensors should be inspected before being replaced, and should not be assumed to be the sole problem causing the P0422 code.

How serious is the P0422 code?

The severity of the P0422 code can greatly vary. If the issue is a faulty catalytic converter, the vehicle may not start, or may frequently stall. In this case, the car will be close to not drivable. However, if the catalytic converter is not the problem, the car should experience little to no issues driving. However, the code should still be addressed as failure to do so may ultimately result in serious damage to the catalytic converter.

What repairs can fix the P0422 code?

Some common repairs for the P0422 trouble code include:

Additional comments for consideration regarding the P0422 code

If the issue causing the P0422 trouble code is a faulty oxygen sensor, then the code will be accompanied by an oxygen sensor trouble code as well.

Auto manufacturers are federally obligated to include a 100,000-mile warranty on catalytic converters. Mechanics should always check to see if the catalytic converter is still under warranty if it is malfunctioning.

Need help with a P0422 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
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