VW POLO 2003 1998 cc petrol Engine Light On

14 Dec 2009
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United Kingdom
My Car Engine Light is ON. I had a scan with VCDS Light. The result is as follows:
VCDS-Lite Version: Release 1.1
Monday, 24 September 2012, 18:14:52.
Control Module Part Number: 03D 906 032 C
Component and/or Version: 1,2l/2V SIMOS3 00HS2501
Software Coding: 00031
Work Shop Code: WSC 00788
VCID: 1E4F5D7B89B9
Additional Info: WVWZZZ9NZ3Y205478 VWZ7Z0C6794547
1 Fault Found:
16804 - Catalyst System; Bank 1: Efficiency Below Threshold
P0420 - 35-00 - -

Any idea how I can pinpoint this fault ? Looks like I am in trouble.

Any help will be appreciated.
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Is the performance of the car affected? You'd be surprised how many times this fault flags up - only to cure itself in time.
Its an exhaust catalytic converter or lambda sensor issue really - but fitting new parts doesn't always give a cure.
John :)
I did not notice any change in Engine performance.

I have done scan in other items. It found additional faults:
2 Faults Found:
01598 - Drive Battery Voltage
07-10 - Signal too Low - Intermittent
00906 - Shareware Version. To Decode all DTCs
28-00 - Please Register/Activate
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you will need to get someone who knows what they are doing with diagnostics and take a look at the live data readings for lambda sensor switching etc
Lambda sensor No2 was the trouble with a Lupo with similar codes. Ensure the connections to both lambda sensors are clean off all corrosion, clear the codes and see how you go. As already said, don't go pegging money at it until you know more.
I have cleared the codes. I drove around 15 miles today. No engine light has come on. No sure if the performance is down a bit. Took it to the garage near my home to check. Nothing found with a scan.
The Engine Light is back on again after many months. Had a scan and same error code.
I had this code on my old Audi as well as P0421 as it was a V6.

The Audi/VW ECUs are notoriously fussy about the performance of the catalytic converter. To the point that sometimes these codes are triggered when fitting non-OEM cats. It basically thinks that the cat is not performing as it should.

This can be down to a malfunctioning lambda sensor but more often it is just that the cat is getting old and isn't performing as well as it should (as far as the ECU thinks). If you are not failing MOTs on emissions and not seeing a drop in performance or MPG then don't worry about it. I drove mine around for over a year with this happening and passed to MOTs in that time.

Clear the codes as the MIL comes on. Don't leave the MIL lit though as that may hide other codes.

If you do fail an MOT most garages will start wanting to replace cats and lambda sensors randomly as they can't be bothered (or just can't) diagnose these faults properly. Find someone who can or you will end up spending a lot of money
Update on my car:

Today I took the car to the garage. The technician has found a leak in the front exhaust pipe which is just after the cat converter. I think the rear Oxygen sensor is inserted into it. I will order a new pipe, clamp and get it fitted. Will let you know how it goes.
Someone just PM me about the outcome of the problem. The pipe was replaced and problem was solved.
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