I'm trying to understand the Trouble Code - P0421 text as follows:

WARM UP CATALYST BELOW THRESHOLD - BANK 1

Any insight would be much oblidged

 

usually this is caused be poor spark wires or plugs. If the ignition system is in poor condition or recently repaired because of misfire it could indicate that the front converter is now burnt up and requires replacement.

 

thanks for the feedback, I'll try changing the spark wires and plugs first and cross my fingers......

 

your telling me i borrowed a obd2 tester, read this code, figured it was a sensor and cleaned everything out (o2 sensor(s), thermostat, water temp sensor, exc exc exc...

when all along it was those shitty splitfire plugs I put in 2 weeks ago.

ain't that some ****?

/me goes to but oem plugs

can't wait to find out if these bosch 7mm wires are ganna be the cause of a code in the near future, their has to be something wrong with them they were only 20 bucks at a local shop.

 

So you went to all that trouble to borrow an OBD2 tester, download the codes and then what - wrong interpretation?

Well, you were right the first time. the error code P0421 refers to the first O2 sensor on the exhaust manifold coming off the engine block where the four ports merge into one pipe.

This particular code was generated in my case besause the heater (wires #2 and #3) on the O2 sensor has gone open circuit - resitance is infinite.

Now that I know what to replace, all I have to do is figure out how to get the old sensor out of the exhaust manifold, and then locate a reasonably priced O2 sensor. Would you happen to know what tool will get this sensor out? An extended 20-21mm socket comes to mind, but then I suppose one has to cut the wires to get the socket into place.

Where did you get your O2 sensors from?

You will probably do alright with the new ignition cables. They aren't the problem associated with this error code, and that comes direct from the service shop at the local dealer (Houston).

Let me know what happens once you clear your trouble code light.

 

hey.

well i didn't get any new sensors, i just removed what i thought would be the problem (o2 sensors, thermo sensors, exc) and the front heated o2 sensor shouldn't be considered for removal unless the resistance between terminals C & D is out of range. The range for the 1.8's is 13ohms @ 68f room temp. Use any generic ohm meter and check the resistance. Make sure you start the car, run it for a second, let it cool back down to room temp for 10 minutes and keep key in ignition with systems charged but engine not running.

Remember some ohm meters require calibration before testing (calibration is usually required) which means hold the terminals of the tester together for a few seconds then probe the points you want to measure.

If its out of range, check a shop manual for proper removal.

points C & D are as follows.

from front of connector:

AC
BD

from REAR of connector (when you look into the prongs)
CA
DB

california uses different sensors, 3 wires. I dont know how they work, I think they are entirely computerized and don't output analog-measurable feedback.