2003 Toyota Camry Check Engine Light Won't Come On

SOURCE: 2003 toyota camry

P0420 is a cat code. Sometimes, you can replace the upstream & downstream air/fuel & O2 sensors, run some good fuel injection cleaner thru it, and that might fix the problem. If not, you may need to replace the cat. Note that the cat is covered under warranty for 8 yrs/80,000 miles. Toyota will replace it if it has gone bad, for free.

SOURCE: check engine light/2003 toyota CE

your car engine may have some hidden problem, suggest you take it to dealer workshop to have you car ECU scan and it will resolve the problem once and for all.

SOURCE: 2001 toyota corolla check engine

Mass Air Flow sensor! Just remove your air filter cover. Go to Auto Zone and purchase some solvent. Spray past the air filter and it should correct the problem. If not, replace the Mass air-flow sensor. This is commonly mistaken for an oxygen sensor. Mine did this and I followed these steps and it fixed the light. BTW, the light stayed on for 5 years before I fixed it. Never hurt anything. It's normally something to do with emissions. Dummy lights. :)

SOURCE: 2003 Toyota Camry Se V6 has a check engine light

I had the same problem, then took my car to an expert repair shop who diagnosed the sensors and
found no problem with the car. They notified the DMV who was unaware of the problem, who then told the repair shop (John's Bascom Automotive) that they will adjust their computer system to allow a "two speed idle test". My bill was $95 and I still have to pay for a smog test after driving around for
a couple of days to clear the computer monitors, a fair amount and I gladly paid it.

John advised me that I'd get no satisfaction with Toyota or the DMV. I went to the dealership where I
bought the car and they said that the smog stations don't know what they're doing. They charge
about $100 and work around the P0500 code but it takes them about two hours to do this. I told
them that I should have been notified about the dyno none-compatability by Toyota and that Toyota
should have notified the DMV beforehand. I wonder how many speed sensors are being replaced by
unknowing smog shops around the state. I got Toyota's main customer support phone number and
will call them Monday. I'm going to get my pound of flesh ($95 worth) from the DMV next week also.

traderralph

SOURCE: Toyota camry 2001emission not ready (Readiness == Fail )

The P0420 code, usually associated with a weak cat converter, is in fact often caused by an ageing (weak) downstream O2 sensor. On both my cars at around 150K miles replacing the downstream O2 sensor was all that was needed to clear the code. No cat replacement was necessary. If one actually spends some time reading the diagnostics procedure for this code, they will find that the O2 sensor diagnostic is the first thing to do before replacing the cat converter. The downstream sensor, the one after the cat converter, gets "lazy" with age. This means that it no longer produces voltage signals as it used to. The result is that the voltage swings that come out of it begins to follow very closely the voltage that is generated by the upstream O2 sensor. When this happens, the car computer thinks the cat converter does not do its job (which might as well be the case too, but the O2 sensor is the first thing to try). With a code scanner with live data stream you can see the voltages coming from the O2 sensors. Check-out my write-up on the 2002 Toyota Prius cat converter replacement on http://www.pbase.com/kocho/exhaust_prius
- I got some details there. And see my comment for Dennis above here too