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P0421 Diagnostic Trouble Code Discussion for June 2008

Warmup Catalyst Efficiency Low (Bank 1)

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Trouble Ticket Help Requests for DTC P0421
Help Request Posted
2002 Kia Optima SE 2.4L Stall, MIL Lamp on, lacks power VIN: KNAGD12682
P0421: Catalyst Efficiency Below Normal (Bank 1). the car runs fine at idle, but under load when driving has low power and will not accelerate over 40 MPH without stalling. The computer codes lead us toward the catalytic converter, however a vacuum test to check for exhaust restriction indicates no restrictio...
June 19, 2008