Tech Tip: Audi’s Check Engine Light Is On, Trouble codes P0421and P0431
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Tech Tip: Audi’s Check Engine Light Is On, Trouble codes P0421and P0431

The Check Engine Light (CEL) is on. Trouble codes P0421 (16805) and P0431 (16815) are set.

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Vehicle Applications:  
2002 Audi A4 Quattro 3.0L, Vin T, Eng Cfg V6, Eng Des AVK
2002 Audi A6 Quattro Avant 3.0L, Vin T, Eng Des AVK, USA/Canada
2002 Audi A4 Quattro Avant 3.0L, Vin T, Eng Cfg V6, Eng Des AVK
2003 Audi A4 Quattro 3.0L, Vin T, Eng Cfg V6, Eng Des AVK

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Customer Concern: The Check Engine Light (CEL) is on. Trouble codes P0421 (16805) and P0431 (16815) are set.

Potential Causes: Defective catalyst or leaking exhaust

Tech Tips: Refer to Volkswagen Technical Service Bulletin (TSB) Group 26 Number 05-03 and Group 26 Number 05-04 for more information concerning this trouble code. If the catalyst appears to operate well, but the trouble code returns, the Engine Control Module (ECM) may need re-flashing.

Tests/Procedures:  
Attempt to force catalyst readiness codes, with a full-function, factory-compatible scan tool, as follows:
1. Clear all trouble codes.

2. Enter Engine Address Word 01, Function 04 “Basic Settings” and Display group 198.

3. Simultaneously press the brake and accelerator pedals and the engine speed will increase to 2,200 rpm. Observe field 2 and 4. Field 2 must show Catalyst B1 OK and field 4 must show Catalyst B2 OK, if the test passes.

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4. Once the test indicates catalysts are OK, then depress the accelerator pedal completely (swiftly) and then release it (brief acceleration to at least 4,000 rpm).

5. Using an infrared thermometer, measure catalyst inlet and outlet temperatures. A good operating
catalyst will be at least 150° F hotter on the outlet.

Courtesy of Identifix.

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