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2002 Toyota Camry 2.4L P0420 Code: How to Identify Which Catalytic Converter is Faulty

Model: 2002 Toyota Camry 2.4 Fault Code: P0420 Posted: 2009-03-17 08:21

I own a 2002 Toyota Camry with a 2.4-liter engine and recently received a P0420 diagnostic trouble code indicating 'Catalyst Efficiency Below Threshold'. No other codes are present. Based on online research, this typically points to a failing catalytic converter. However, my OBD-II scanner does not specify which of the two converters is at fault. My car has two catalytic converters: one integrated into the exhaust manifold and another located just past the flex pipe. My budget is very limited—barely enough for one replacement—and I’m trying to determine how to identify which converter is actually failing without spending on both. I’ve also read that a faulty oxygen (O2) sensor might trigger a P0420 code. Is this accurate? Can the issue be caused by an O2 sensor rather than a catalytic converter? Any advice or troubleshooting steps would be greatly appreciated.

Related fault codes

P0420

Comments (5)

Anonymous 2009-03-18 05:15

The P0420 code can indeed be triggered by a faulty oxygen sensor, especially the downstream O2 sensor. To accurately diagnose which component is at fault, you’ll need a lab-grade scope to monitor O2 sensor voltage signals during engine operation. While I’m not familiar with your specific model, most 2002 Toyota Camry 2.4L vehicles have two upstream and two downstream O2 sensors. You can also contact your dealership with your VIN to check for any Technical Service Bulletins (TSBs) related to this issue.

Anonymous 2009-03-18 07:23

Thanks for the input! The dealer confirmed there are two oxygen sensors—one upstream and one downstream. It sounds like I’ll need a full inspection at the shop, which is what I’m planning to do next.

Anonymous 2009-03-18 08:58

The 2.4L 4-cylinder engine in this model has only one oxygen sensor upstream of the catalytic converter and one downstream O2 sensor. The most likely cause of the P0420 code is either a failing catalytic converter (there’s only one) or a faulty downstream O2 sensor. With proper tools and knowledge, you can diagnose the downstream O2 sensor without professional help. However, given your situation, it may be best to let professionals handle the repair.

Anonymous 2009-03-18 19:25

Thanks for the clarification! I’ve taken photos of both catalytic converters—both look similar under the hood (though one appears slightly more worn). The first photo shows the second converter (after the flex pipe), and the second shows the one integrated into the exhaust manifold. I can see that the upstream O2 sensor is located before the first cat, and the downstream O2 sensor is after the flex pipe. I haven’t taken it to a shop yet—just waiting for funds. Emissions inspections are coming up soon.

Anonymous 2009-03-18 20:02

Ah, now I understand! You might want to reach out to Toyota’s service department and inquire about TSB #02404, which may be covered under an extended emissions warranty. Here's the full bulletin: http://www.justanswer.com/uploads/skyvi...04_cam.pdf Component Description: 12. ENGINE AND ENGINE COOLING: ENGINE Bulletin Number: 02404 Bulletin Date: JUL 2004 Vehicle: 2003 Toyota Camry Summary: MALFUNCTION INDICATOR LAMP ON WITH DIAGNOSTIC TROUBLE CODE P0420 (NHTSA ITEM NUMBER - 10009703)