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2003 Toyota Camry P0420 Code: Causes, Fixes, and Smog Test Tips for California Drivers

Model: 2003 Toyota Camry Fault Code: P0420 Posted: 2008-05-01 16:57

I own a 2003 Toyota Camry with a 4-cylinder engine and automatic transmission. I've been experiencing a check engine light for at least 18 months, and recently the vehicle has triggered a P0420 code — specifically, two instances of P0420 (with two symbols resembling a yin/yang formation) when scanned at AutoZone. The car has otherwise driven smoothly with no noticeable performance issues; however, the check engine light occasionally turns off but returns within one to two days. I initially took it to Toyota service while still under warranty, but they were unable to perform diagnostics due to a scheduling conflict — only offering appointments on specific weekdays that I could not attend. Now, after registering in California, I must pass a smog test, and the check engine light will cause me to fail. The P0420 code indicates a failure of the catalytic converter or related components such as oxygen sensors. While this issue can stem from various causes — including faulty O2 sensors (up to $160 each with installation) or a failing catalytic converter (ranging from several hundred to nearly $2,000 depending on whether only the cat is replaced or the entire exhaust system is involved), I'm seeking reliable guidance on what steps to take. I’ve read that some Toyota models from this era have known factory bulletins related to P0420 issues. Additionally, resetting the code prior to smog testing may allow temporary clearance — typically requiring 2–3 driving cycles with normal operation before the code reappears. Any insights or recommendations on diagnosing and fixing this issue would be greatly appreciated.

Related fault codes
P0420
Comments (3)
Anonymous 2008-05-02 06:43

For detailed information about P0420, visit: http://www.obd-codes.com/p0420. If you're unclear about any part of the explanation, feel free to ask — we’re here to help.

Anonymous 2008-05-02 08:55

The catalytic converter on a 2003 Toyota Camry is typically covered under an 8-year or 80,000-mile warranty. There are also official factory service bulletins addressing this issue. I recommend contacting your local dealer to schedule a repair under warranty.

Anonymous 2008-06-02 18:58

I've faced the same P0420 problem for years and have found Toyota's responses to be inconsistent. The code can point to multiple causes — from two or more oxygen sensors to a failing catalytic converter. In my case, I initially had engine oil sludge issues, which led to a full engine replacement — but the check engine light has returned since. From various forums and reviews, one of the most cost-effective solutions is purchasing an OBD-II scanner for around $50 from Harbor Freight or similar retailers. Before your California smog inspection, try resetting the error codes. After 2–3 normal driving cycles with consistent operation, the code may reappear — this method has helped me pass smog tests successfully over four years. That said, if a fix is needed, an O2 sensor replacement might be sufficient (though each can cost $160+ including labor), while a catalytic converter replacement could range from hundreds to nearly $2,000 depending on whether only the cat or the entire exhaust system is replaced. It's frustrating — I've noticed Toyota service often makes arbitrary choices about what parts to replace. Honda seems more transparent in this regard. Best of luck with your fix! — Moz