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

- Code Popularity: 37,073 Views
- Repair Importance Level: 2/3
- Repair Difficulty Level: 2/3
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What are the Possible Causes of the DTC P0421 Audi?

NOTE: The causes shown may not be a complete list of all potential problems, and it is possible that there may be other 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
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How to Fix the DTC P0421 Audi?

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.

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What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0421 Audi 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?

The P0421 code is set when the Engine Control Module (ECM) detects rear HO2S value difference becomes closer to value of front HO2S. The ECM monitors when vehicle speed is 25-60 MPH, load is 22-45 percent and engine speed is 1000-3000 RPM.

What are Code Possible Symptoms?

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

Code P0421 Audi Description

The Engine Control Module (ECM) monitors the switching frequency ratio of heated oxygen sensors 1 (front O2 sensor) and heated oxygen sensors 2 (rear O2 sensor).
A three way catalyst converter (Manifold) with high oxygen storage capacity will indicate a low switching frequency of heated oxygen sensor 2. As oxygen storage capacity decreases, the heated oxygen sensor 2 switching frequency will increase.
When the frequency ratio of heated oxygen sensors 1 and 2 approaches a specified limit value, the three way catalyst malfunction is diagnosed.

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

Need More Information on the Code?

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Code P0421 Audi comments

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