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P0420 Diagnostic Trouble Code Discussion for July 2014

Catalyst Efficiency Below Normal (Bank 1)

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Trouble Ticket Help Requests for DTC P0420
Help Request Posted
2001 Toyota Sienna LE 3.0L MIL Lamp on VIN: 4T3ZF13C71
P0420: Catalyst Efficiency Below Normal (Bank 1). replaced rear oxygen sensor about 3 day before same trouble code came back on have any ideas as to what may be the problem?
July 20, 2014
1996 Nissan Pickup SE 2.4L Stall VIN: 1N6SD16S9T
P0420: Catalyst Efficiency Below Normal (Bank 1). Vehicle intially came in for Stalling at stops. Scanned the vehicle and came up with the afore mentioned codes. Owner declined to do anything about it at the time. Three weeks later the stalling was worse so they brought it in for repairs. Road tests to verify...
July 21, 2014