Mechanics

MIL CODE P0420

1999 Honda Accord

Engine Performance problem
1999 Honda Accord 4 cyl Front Wheel Drive Automatic 104000 miles

i have a problem with the same code (P0420) coming back. I own a actron auto scanner model cp9180. I look the code up and I get catalyst efficiency below threshold bank 1. And when I look at the freeze screen all different reading seem to be within their value range meaning they seem to be reading normal except for the (st ftrm1 %= -7.7) (lt ftrm1 %= -9.2) (st ftrm3 %= -100.6) (lt ftrm3 %= -100.6) these mean short term fuel trim bank 1 =st ftrmX bank 1 and bank 3. Bank 1 and bank 3 long term air to fuel ratio correction factor = lt ftrmX. I really don't know what all this really means. I recently did a small tune up plugs, oil and oil filter, air filter. The only other thing I could think of is to change plug wires and distributor cap and rotor. I am a little mechanically inclined more than the average joe. But these newer cars there is a lot of electronics that run the vehicle. So if you could please help me with any info or point me in the right direction I would be very greatful. Thank you for your time and effort.
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Rgo82
February 24, 2010.




Hi rgo82, Welcome to 2carpros and TY for the donation

Check and test the oxygens sensor/s, coolant temperature sensor, and for exhaust leak if all are okay its gonna end up being the catalytic converter

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

Tiny
Rasmataz
Feb 24, 2010.
Well I have some of that info for you. This is all the info the scanner has provided to me in the freeze data

ABSOLUTE TPS % = 21.1
ENG SPEED RPM = 2209
CALC LOAD % = 65.0
MAP KPA = 66
COOLANT IN F = 161
IAT IN F = 123
VEHICLE SPEED IN MPH = 56
FUEL SYSTEM 1 = CLOSED
FUEL SYSTEM 2 = N/A

UNDER THE I/M MONITORS
MISFIRE MONITOR = OK
FUEL SYSTEM MON = OK
COMP COMPONENT = OK
CATALYST MON = OK
HTD CATALYST = N/A
EVAP SYSTEM MON = INC
SEC AIR SYSTEM = N/A
A/C REFRIG MON = N/A
OXYGEN SENS MON = OK
OXYGEN SENS HTR = OK
EGR SYSTEM MON = OK

UNDER O2 MONITOR TEST
O2 BANK 1 SENS 1
TEST ID $30
MAX = 2.0(S)
MEAS = 0.4(S)
MIN = 0.0(S)
MOD $0E

O2 BANK 1 SENS 2
TEST ID $45
MAX = 0.800(V)
MEAS = 0.565(V)
MIN = 0.290(V)
MOD $0E

I ALSO HAVE A QUESTION ON HOW TO TEST THESE SENSORS THAT YOU MENTIONED. TO I TEST THE RESISTIVITY OF THE SENSORS IF I GET A HIGH RESISTIVITY THE SENSOR IS GOOD IF I GET 0 RESISTANCE THEN THE SENSOR IS DEAD. PLEASE CONFIRM IF THIS IS TRUE OR IF THERE ARE DIFFERENT WAYS TO TEST. I REALLY APPRECIATE THE TIME AND EFFORT TO ANSWER MY QUESTIONS.
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Tiny
Rgo82
Feb 24, 2010.
Testing the oxygen sensor:

Tiny
Rasmataz
Feb 25, 2010.

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