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P0420 Diagnostic Trouble Code Discussion for September 2012

Catalyst Efficiency Below Normal (Bank 1)

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Trouble Ticket Help Requests for DTC P0420
Help Request Posted
1996 Mercury Grand Marquis LS 4.6L MIL Lamp on VIN: 2MELM75W7T
P0420: Catalyst efficiency below limit b1. ... check engine light on. The code were p0171,po174, and p0430, explained the situatuion to the customer and replaces mass air flow meter and waited to see if p0430 returned. the code did return so we replaced the left converter asssembly and told the custome...
September 05, 2012
2003 Chevrolet Impala LS 3.8L MIL Lamp on VIN: 2G1WH52K13
P0420: Catalyst System Low Efficiency. repeat P0420 code.replaced conv 3x. no coolant loss,uses 1 qt oil per service, replaced o2 both,conv temp 550 frt/650+ rear, hot rear O2 600-640mv fairly flatline. calc load max of 87%. when code stores(freeze frame)closed loop,LTFT has been 126 and 129 not ri...
September 17, 2012