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P0421 Hyundai Code - Warm Up Catalyst Efficiency Below Threshold Bank 1

- Code Popularity: 24,439 Views
- Repair Importance Level: 2/3
- Repair Difficulty Level: 2/3
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What are the Possible Causes of the DTC P0421 Hyundai?

NOTE: The causes shown may not be a complete list of all potential problems, and it is possible that there may be other causes.
  • Three way catalyst converter Bank 1
  • Exhaust tube
  • Intake air leaks
  • Fuel injectors may be faulty
  • Fuel injector leaks
  • Spark plugs may be faulty
  • Improper ignition timing
  • Engine Control Module (ECM)
⚠ Does your Hyundai have Safety Recalls? → Check here

How to Fix the DTC P0421 Hyundai?

Review the 'Possible Causes' mentioned above and visually examine the corresponding wiring harness and connectors. Ensure to check for any damaged components and inspect the connector pins for signs of being broken, bent, pushed out, or corroded.

Code Tech Notes

As the code description implies the P0421 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 P0421 code is combined with other codes, try fixing the other codes first.

Search for P0421 Hyundai Questions and Answers: Search here →

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0421 Hyundai code, it typically requires 1.0 hour of labor. The specific diagnosis time and labor rates at auto repair shops can differ based on factors such as the location, make and model of the vehicle, and even the engine type. It is common for most auto repair shops to charge between $75 and $150 per hour.

When is the Code Detected?

- Three way catalytic converter Bank 1 does not operate properly.
- Three way catalyst converter Bank 1 does not have enough oxygen storage capacity.

What are Code Possible Symptoms?

  • Engine Light ON (or Service Engine Soon Warning Light)

Code P0421 Hyundai Description

The catalyst’s efficiency is demonstrated by its ability to oxidize CO and hydrocarbon emissions. The Powertrain Control Module (PCM) compares the output signals of the front and rear oxygen sensors to determine whether the output of the rear sensor is beginning to match the output of the front oxygen sensor. Air/fuel mixture compensation keeps the frequency of the front oxygen sensor high due to the changes from rich-to-lean comvustio. The catalyst causes the rear oxygen sensor to have a lower frequency. As the catalyst wears, the rear oxygen sensor’s signal trace begins to match the front oxygen sensor’s signal trace. That is because the catalyst becomes saturated with oxygen and cannot use the oxygen to convert hydrocarbon and CO into H₂O and CO₂ with the same efficiency as when it was new. A completely worn catalyst shows a 100% match between the frequency of the front and rear sensors.

OBDII Code P0421 Hyundai - Warm Up Catalyst Efficiency Below Threshold Bank 1 - AutoCodes.com
P0421 Hyundai Code - Warm Up Catalyst Efficiency Below Threshold Bank 1

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Code P0421 Hyundai comments

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