P0420 Code on 2003 Toyota Camry XLE

When I purchased my 2003 Toyota Camry XLE from a friend, he indicated to me that the check engine light was on.  The central Ohio Toyota dealer had told him that it was probably just an oxygen sensor and to not worry about it.  The car would produce a little more pollution but would run fine.  The dealer had quoted him in the neighborhood of $700 to replace both sensors.  The dealer also wanted $95 to determine what had triggered the check engine light to come on.

After I obtained the car, I took it down to the local Advance Auto and had them read the code for free.  Result – P0420:

Catalyst system efficiency below threshold – bank 1

Probable cause:
1 – air leak in exhaust before rear oxygen sensor;
2 – Air/fuel sensor error;
3 – Fuel system fault; or
4 – faulty catalytic converter.

This Toyota has an air/fuel sensor in the front which is supposed to be more accurate than an oxygen sensor.  From what I understand, the computer can take readings from the air/fuel sensor and make finer adjustments with the air/fuel ration than a normal oxygen sensor.

On my way over to have my mechanic check it out, the check engine light turned off.  My mechanic spent a couple days with it trying to get it to turn back on but with no luck.  I consulted the original owner who said that it would come on during the winter months and turn off during the summer months. I’ve seen speculation that gas company change their fuel mixture from winter to summer and perhaps the Camry doesn’t like the winter formulation.

After a bit of research on the internet, it appears 2002-2004 camry’s have a known issue with the front catalytic converter failing and giving this code.  Toyota even put out a service bulletin to that effect as well as stating that the ECM would need to be recalibrated and that they had a redesigned converter:

TSB EG024-04, July 1, 2004

M.I.L. “ON” DTC P0420 [Note: M.I.L. = Malfunction Indicator Lamp = Check engine light]
‘02 – ‘04 Camry (2AZ-FE) (Non PZEV)

Some 2002 – 2004 model year Camry vehicles equipped with the 4 cylinder (2AZ–FE) engine may exhibit a M.I.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.

MODEL Camry (2AZ-FE)
TMM Kentucky Line 1: 4T1BE3#K#4U323000
TMM Kentucky Line 2: 4T1BE3#K#4U869000
Tsutsumi Japan: JTDBE3#K#40283686

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.

Recalibrate Engine ECM (PCM)
R & R Catalytic Converter Assembly

All 2002 – 2004 model year vehicles equipped with manual transmissions require replacement of the catalytic converter assembly only.

I’m hoping not to have to replace the front catalytic converter. In the meantime, I picked up a new air/fuel sensor and installed it. At the time, the Camry had about half a tank of gas in it. My gas mileage immediately jumped from 19.48 (previous tank) to 23.25 (current tank of gas). I’ll be interested to see what my next mpg reading is (new sensor will have been in for the entire tank of gas this time).

Removing air/fuel sensor from Toyota Camry

I’ve read elsewhere that a bad catalytic converter will go through oxygen sensors rather quickly. I imagine if I just keep an eye on the mpg, I’ll know when there’s a problem.

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