P0421 warm up catalyst efficiency below threshold bank 1 code what does this mean? car is a 2004 lancer oz plz help

 

go to local mitsu dealer for the recall and search the forums here

 

k thanks

 

k so the light went off by itself what does that mean i didnt reset it or anything just went off on its own

 

its a common problem with our cars man you could type that code in our search field and get a wealth of info on it. Its a recall from mistu, they will first try to flash your ecu and if that doesnt work they will replace your cat free, they did that for me.

 

i got this code 1 year ago, it turned out to be my catalytic converter and 02 sensor, replaced with Obx HF cat and new 02 sensor.

the following is from AllData

P0421



TECHNICAL DESCRIPTION

The signal from the rear heated oxygen sensor differs from the front heated oxygen sensor. That is because the catalytic converter purifies exhaust gas. When the catalytic converter has deteriorated, the signal from the front heated oxygen sensor becomes similar to the rear heated oxygen sensor. The ECM or PCM compares the output of the front and rear heated oxygen sensor signals.

DTC SET CONDITIONS

Check Conditions
Engine speed is lower than 3,000 r/min .
Volume air flow sensor output frequency is at between 70 and 150 Hz .
Intake air temperature is higher than -10 °C (14 °F) .
Barometric pressure is higher than 76 kPa (11 psi) .
The throttle valve is open.
Under the closed loop air/fuel ratio control.
Vehicle speed is 1.5 km/h (0.93 mph) or more.
Monitoring time: 12 seconds x 7 times .
Short-term fuel trim is at between -25 and +25 percent.
The cumulative volume air flow sensor output frequency is higher than 4,000 Hz.

Judgment Criteria
The heated oxygen sensor (rear) signal frequency divided by heated oxygen sensor (front) signal frequency = 0.75 or 0.8 or more.

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are
Catalytic converter deteriorated.
Heated oxygen sensor failed.
ECM failed.
PCM failed

 

wish i new about the new cat,, before i already paid for it, when i got the new exhaust system installed. just got the pcm reflashed, and its messing with my tranny man,,, had to replace neutral safety switch and my tranny isn't down shifting correctly, or at least its not like it was before the reflash, granted 1st gear is a lot quicker, but thats bout it