Exhaust warning light - o2 sensor or cat?

[Milos2504]

My exhaust emission warning light has been coming on and off in the last few months. Last time I had the car services they just cleared all the codes and didn't mention it, when I asked about it they said it could be the sensor going bad.

Since then I have notices a few weird things.

- When I start the car in the morning it sort of struggles a little - the car starts, but it seems like a few months ago it used to start much quicker.
- Some mornings I hear a banging noise, it sounds like the exhaust is loose so I go outside the car to check it but everything seems fine
- And the Exhaust warning light comes on for about a week then goes away then comes back on after a while.

I did a bit of research and saw that it could be a catalytic converter going bad. How do I check if this is the case, or would it just be the o2 sensor? Can I replace the sensor myself, is there any DIYs on this?

Any help is much appreciated

[gazzmo]

I assume you are not running an exhaust mod / dp?

Who services your car and clear warning lights without an explaination? If it is an O2 sensor then I would get a Vagcom scan to see which one as there are 2 one each side of the cat, then I would swap the sensors over and rescan to see if it is the same location fault if it is then it is either the wiring to the sensor or bad cat. If the fault changes to the other location then good chance its a bad sensor. Don't go getting one until having it scanned.

Changing the O2 sensor is not hard just need a 22mm open ended spanner have the car raised to gain access, the front sensor needs to be unplugged from inside of the engine bay just toward the cabin from the ABS control box, there are DIYs out there if you get stuck.

[Milos2504]

They didn't clear the code because the warning light turned off before I went to the mechanics, but I don't know if there is a history of error codes that come up from service to service.

I service the car in VW Centre Belconnen, in Canberra. I guess I will have to give them a call.

[Milos2504]

Went past VW Centre today and I was told I have to replace the charcoal canister, which apparently costs $250 but has no affect on the car or performance, so I decided to leave it. Has anyone had this problem before? If so where would be the best place to buy one, and can it be replaced without VAGCOM or does it need some sort of coding?

[vdubmotorworx]

Common on golf 5. Open the bonnet and look to the left front and you will see the canister with a round valve on top with a rubber pipe going to the engine and plastic pipe towards the fuel pipe area. You can lift out and fit yourself no vcds required. The filter will be full.

[Milos2504]

Common on golf 5. Open the bonnet and look to the left front and you will see the canister with a round valve on top with a rubber pipe going to the engine and plastic pipe towards the fuel pipe area. You can lift out and fit yourself no vcds required. The filter will be full.

Thanks mate, do you know where I can buy them from? Do they really cost $250?

[vdubmotorworx]

Not sure on price. Just ring another dealer parts department and quote on the part only

[snerlo]

Just so that you know, i think it was this light we had on over 12 months ago and we were told that the canister is getting clogged due to overfilling when refueling. You know how the pump generally clicks, and then you try and squeeze a few more seconds worth in the tank, don't. Just pull out and close the cap. Apparently this is the cause. Don't overfill your car. Dunno if this is true but we used to squeeze some more in the tank and now we have stopped!

[Corb13]

I have had the same issue with a little bit of a rough start and engine light on, my mechanic said the same thing about refuelling and not filling it past the click due to overflow. I havent refuelled since and it has come back on. Getting it checked again today.

[Milos2504]

Thanks for the advice guys. I don't overfill it that often maybe I've done it couple of times.. But I definitely don't do it any more..
I think that once the filter gets clogged up it just needs replacing but considering it doesn't affect the performance I don't really want to spend money on it. I would rather buy VCDS cable for a bit more money and turn the light off myself every time it comes on