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P0420 and Front Sensor

11-25-2011, 10:30 AM
In July 2010 the CEL came on in my daughter's '98 Camry 4cyl (California emissions). I Don't remember the code but I replaced the rear sensor and CEL has been off for the last 16 months (23K miles). Now at 135K the CEL is on again with code P0420. I've checked for exhaust leaks are there are none.

Question: What are the chances it's the front sensor? The FAQ lists front sensor as the second most likely cause after leaks. Yet none of the posts I've read here (after searching for P0420) talk about replacing the front sensor.

11-25-2011, 09:41 PM
I hope this helps:

TSB No. EG013-04

Quote: “Some 2002 - 2004 model year Camry vehicles equipped with the 4 cylinder (2AZ-FE) engine may exhibit a M.l.L. ON" condition with Diagnostic Trouble Code (DTC) P0420 (Catalyst System Efficiency Below Threshold, Bank 1) in the Engine Control Module (ECM) (SAE term: Powertrain Control Module/PCM). The ECM (PCM) logic has been modified and a redesigned catalyst has been provided.
NOTE :The repair procedure in this TSB is similar to TSB No. EG013-04 "Excessive Sulfur Dioxide Odor." The recalibration of the ECM (PCM) should only be performed ONCE.”

Good luck,

11-26-2011, 06:59 AM
Somick, Thanks for the info. My daughter's Camry is a '98 (Gen4) so that TSB probably doesn't apply.

Since I have a short window of opportunity (she was home from school only for the thanksgiving holiday) I went ahead and replaced the upstream sensor (Bosch - $117).

Will post in a week or so on whether this resolved it.

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