code 420 03' Camry

[TerryWalter]

Hi All,

Have a 03 Camry with 2.4 L motor and 147.000 miles. Had a blown head gasket (stripped threads on 2 head bolts) repaired about 2 1/2 years ago at 109.000 miles. Other than that car has ran good.

For the past year or so the check engine light has been coming on and going off with a 420 code. During the summer the light stays mostly off and as the weather starts getting colder the light comes on and stays on longer.

We get about 28 mpg and the car runs great. No power loss or slugishness, etc. I measured the temperature before and after the converter and it read as follows, 350 before and about 390 after the converter.

According to our local Auto parts store it could be a number of things (see attached document) like air leak or AF sensor error besides the converter. How can I tell which parts need replacing? The sensors each run about $120.00 and the converter is about $220.00 and I install it myself. I don't mind spending the money but I don't want to throw it away on parts that have not gone bad yet. Any help would be appreciated.

[Brian R.]

First check for leaks in the exhaust system between the engine and the cat converter (loose connection, rusted area, or burned out seal)

If no obvious problem with exhaust leaks, test the HO2 sensor after cat converter (remove connector and measure resistance between terminals +B and HT - should be 11-16 ohms). Replace if out of spec. This is the most likely problem

Then test the HO2 or A/F ratio sensor before cat converter (remove connector and measure resistance between terminals +B and HT - should be 1.8 - 3.4 ohms or 11-16 ohms depending on whether you have an HO2 or A/F ratio sensor). You most likely have an A/F ratio sensor.

If both these test good, cat converter is bad.

If you need to replace a sensor, bring your VIN to a Toyota dealer and get the correct part number for your engine. There is only one that works correctly, but at least two available. You don't have to buy the part from Toyota, but you have to have the correct part number. Get the DENSO part number from the DENSO web site, using the Toyota part number:

http://densoproducts.com/resultsApp.asp

Then check Amazon.com for the DENSO part. Most likely they have the best prices.