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Check Engine Light - Low Catalyst Efficiency


akellen
09-17-2003, 12:53 PM
I have a 2000 Passat GLX (2.8L V6). Lately, I've been getting the check engine light every 100-200 miles. The light generally comes on when I'm driving at freeway speed; often upon deceleration. Using my code reader, I get two trouble codes: P0421 - Warm Up Catalyst Efficiency Below Threshold (Bank 1) and P0431 - Warm Up Catalyst Efficiency Below Threshold (Bank 2). I doesn't seem like the problem can be "real," since I get both codes at the same time. Any idea what could be causing this?

tallngangly
02-07-2004, 03:39 PM
Yesterday the same codes popped up on *my* 2000 2.8L Passat. Did you ever figure out what was wrong? Any info would be appreciated.

boschmann
02-08-2004, 04:09 PM
If both codes are coming up at the same time, I wouldn't suspect cat or O2 sensors. Make sure the vehicle is getting to proper temperature, mainly that the thermostat isn't stuck open.

tallngangly
02-11-2004, 06:24 PM
Thanks for the suggestion, boschmann. It looks like the coolant temp is acting OK (based on the display in the instrument cluster), but I did notice something odd when warming up...

Normally the auto transmission will delay the upshift to 2nd gear until ~3000rpm when starting cold (so that the cat will warm up more quickly), however it isn't doing this anymore. It upshifts just like it does when the vehicle is at normal operating temp. Obviously, this might be the cause of the warm-up cat performance problem, but then the question becomes why doesn't the transmission delay the upshift any more? Puzzling.

boschmann
02-12-2004, 10:53 PM
I would check the temp issue a little further. Does your scanner have a way of monitoring the coolant temp data from the ECT sensor as the vehicle warms up? Alternately, you can check resistance at the sensor: 1500-2000 Ohms @ 86F with a progression to 225-275 Ohms @ 194F (operating temp).

tallngangly
02-22-2004, 04:38 PM
Well, after about a week wth the MIL light on, it went away and hasn't returned. If/when it returns, I will try to do some more sleuthing....

Trillion4245
02-27-2004, 01:54 PM
Follow this thread & find a tip >
'AGAIN! Check Engine & Emissions Workshop Warnings'

warangel
03-01-2004, 05:36 PM
the best procedure for working on new cars,is to buy the service and electrical manual from yor dealer this will tell you where all the parts are and auto codes. invest in a scanner with obd1 and obd11 auto xray scanner forv about 400.00 dollars this will save you a lot of headaches and a lot of money. the mechanics have you by the balls when you have any electrical problems,the scanners are easy to use, if you could use a copmputer you could use a scanner.the top of the line are the auto xray 5000 or the 6000 x-ray. :smokin:

warangel
03-01-2004, 05:38 PM
the best procedure for working on new cars,is to buy the service and electrical manual from yor dealer this will tell you where all the parts are and auto codes. invest in a scanner with obd1 and obd11 auto xray scanner forv about 400.00 dollars this will save you a lot of headaches and a lot of money. the mechanics have you by the balls when you have any electrical problems,the scanners are easy to use, if you could use a copmputer you could use a scanner.the top of the line are the auto xray 5000 or the 6000 x-ray. :smokin: not fair to post one message every thirty seconds

hyundai jw
08-03-2006, 12:16 AM
i have a 2000 accent 1.5l sohc with a code PO422 that says the main catalyst efficiency for bank 1 is below threshold for the current engine operating conditions. I had the guy at autozone reset the computer for me but 35 miles down the road the light came back on. What is it that I need to replace on the car to get it back to normal operating conditions?

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