Catalyst Error

sinlessUK

sinlessUK

Member
Had this come up in VCDS but no lights appeared on the dash. Question is which CAT or sensor does this relate to in the following link http://tinyurl.com/jclgelu

16804 - Catalyst System; Bank 1: Efficiency Below Threshold P0420 - 35-00 -

This used to appear and still does after a new exhaust system, including CAT, (No3 in the link above). Only thing I've haven't changed are the sensors or No1 CAT.

Kindest Regards
 
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Hi it is worth checking to see if the system has any leaks. Likewise check that the small corrugated egr pipe has not cracked-either will allow oxygen rich air to enter the exhaust flow tricking the sensors. Cheers Mike
 
a2sumo said:
Hi it is worth checking to see if the system has any leaks. Likewise check that the small corrugated egr pipe has not cracked-either will allow oxygen rich air to enter the exhaust flow tricking the sensors. Cheers Mike
Click to expand...

Shall check the EGR pipe but CHB replaced that for me just over a year ago. Do you know which sensor produces this code? Pre or post CAT as neither have been replaced.

I've got the MOT next Monday :(
 
So it's passed the MOT (Tuesday). Drove home and halfway into the journey the ‘Engine Light’ came on (no loss in performance) so pulled over and did a full VCDS scan. Only error to be found was the one above. Went into VCDS > 01.Engine > Readiness and everything says passed, (usually the Catalyst is failed/incomplete). Strange as to why it has only just decided to come on and tell me now. Anyway I cleared the fault, ‘Engine Light’ off and away we go.

Now up until today, (Thursday AM) I’ve had a juddering/misfire when maintaining engine speed. Only happens with little or no load on the engine. If I maintain the speed, it free's itelf up and then happens again.

Could the sensor be dodgy causing it to misfire and need replacing?
 
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I have the two sensors that are just below the outlet manifold if it turns out you need them. I took them from Hilaries car for safe keeping for a forum member (or me!) if I needed them.
 
I had a painstaking process of fixing this error.

Primary catalyst was replaced and error still appeared.
Ultimately, reason was burnt exhaust valves and head had to come off with all valves reseated and error subsequently fixed.

Can't quite remember the details why this triggers the error, but 1yr on code hasn't ever reappeared.
Was rather expensive - around £2000 more than the car is worth for all of this work, done by a VAG specialist.

Hope you get it sorted- they're worth the investment.

Pete
 
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