1996 Toyota Camry P0420/Check engine light

Tiny
BERNC032
  • MEMBER
  • 1996 TOYOTA CAMRY
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 160,000 MILES
I had my car checked at a place to see why my check engine light came on. It said P0420, catalyst system efficiency below threshold-bank 1, and gave the possiblities of air leak in exhaust before rear HO2S (bank 1), AF sensor error, fuel system fault, and faulty catalytic converter. What does bank 1 mean? What might fixing the fuel system fault problem entail? If bank 1 means most likely cause, what would fixing the HO2S entail?
Do you
have the same problem?
Yes
No
Friday, February 26th, 2010 AT 4:50 PM

2 Replies

Tiny
RASMATAZ
  • MEMBER
BK1 means where the no.1 sparkplug at-could be 02 sensor to include the CTS and defective Cat

Causes Of Converter Failures

Fouling, clogging, melt-down and breakage of the ceramic substrate inside a converter are common conditions that can cause problems. Plugging is usually the end result of a melt-down, which occurs because the converter gets too hot. This happens because the engine is dumping unburned fuel into the exhaust. The excess fuel lights off inside the converter and sends temperatures soaring. If it gets hot enough, the ceramic substrate that carries the catalyst melts.

The unburned fuel may be getting into the exhaust because of a bad spark plug or valve, but an overly rich air/fuel mixture is another possibility. In older carbureted engines, a heavy or misadjusted carburetor float may be the underlying cause. But on newer engines with "feedback" carburetion or electronic fuel injection, the engine may not be going into "closed loop" (the normal mode where the computer regulates the air/fuel mixture to minimize emissions).

A bad oxygen sensor or coolant sensor may be giving the computer bogus information. A sluggish or dead O2 sensor will make the computer think the exhaust is running lean, so the computer will try to compensate by making the fuel mixture rich. A coolant sensor that always indicates a cold engine will also keep the system in open loop, which means a steady diet of excess fuel. But it might not be the sensor's fault. A thermostat that's stuck open or is too cold for the application can prevent the engine from reaching its normal operating temperature. So if your converter has failed and needs to be replaced, the engine should be diagnosed for any underlying problems before the new converter is installed.

Another cause of converter clogging and contamination is excessive oil consumption. Worn valve guides or seals can allow oil to be sucked into the engine's combustion chambers. The same goes for worn or damaged rings or cylinders. Oil can form a great deal of carbon, and metals present in the oil can contaminate the catalyst. A compression check or leak-down test will tell you if the rings are leaking, while a fluttering vacuum gauge needle will help you identify worn valve guides.
Was this
answer
helpful?
Yes
No
Friday, February 26th, 2010 AT 4:58 PM
Tiny
BERNC032
  • MEMBER
It's probably unrelated, but I noticed in the last few weeks that the RPM gauge has been creeping up beyond 3-4 when I accelerate whether it's going up hill or to overtake someone on the highway. And the car is a bit louder than normal when I accelerate. I think I've had a bad calatytic converter before (first car, about 6 years ago, diagnosed by mechanic). It sounded like I'd tricked out the exhaust on the car when I accelerated and was speeding away, but really I was barely moving.
Was this
answer
helpful?
Yes
No
Friday, February 26th, 2010 AT 5:30 PM

Please login or register to post a reply.

Recommended Guides