Help requried in diagnosing engine fault codes
 

Hello

I'm intermittenlty getting the below codes:


16804 - Catalyst System; Bank 1: Efficiency Below Threshold

16814 - Catalyst System; Bank 2: Efficiency Below Threshold

17831 - Secondary Air Injection System; Bank 1: Insufficient Flow

17819 - Secondary Air Injection System; Bank 2: Insufficient Flow

I have already replaced the top part of crank breather hose, I will be doing the bottom left hand side and the little plastic vacuum pump next along with removing the inlet manifold and replacing throttle body gasket and inlet manifold gaskets.

Is there anything else I should be looking at? I think re-doing all the vacuum tubing wouldn't go a miss.

I would start with the vacuum tubing. My car is an S8 so I don't know specifically how the system on your car is set up but I have had 2 secondary air injection faults over the last 2 years and both were leaking vac pipes. In the end I replaced all the pipework. A vac pump would be useful to test the pipe work and VCDS to output test the pump if you have access to them.

I was going to say vacuum pipes too. The valves for the SAI are vacuum driven so if there is a leak they may not be operating.

Cat efficiency below threshold seems to be a common problem with the 2.8. Big Red does it too from time to time. It may simply be time for new cats unfortunately. MoT on Friday so we'll see what readings that gets...

Vacuum pipes it is then!

Which pipes do you recommend? I knowthe part number for a VW 1m lenght of it is 059130329 but its like 39.99 on ebay which is stupid :mad:

I owned a 2002 Audi A4 3.0 up until a couple of years ago and that kept throwing up a catt efficiency code. There was some talk about the perameters being set too tight right from the factory. It always passed it's emissions part of the MOT easily.

The constant MIL light did bug the hell out of me though so I had to sort it. I tried new pre and post catt O2 sensors but to no avail. Catta clean in the fuel, also no good. I didn't want to spend the £1500 on a new down pipe and catts so waited for a second hand one to come up for sale. I took the car and the replacement catt to a local custom exhaust shop, paid em £100 to cut out the old catt and weld in the replacement. All done in situe on the car. No more problems.

I have actually had to do the same on the S8 but that was because of a rattling catt.

A problem you may come across is actually finding a second hand catt. Most breakers sell em on for recycling quite quickly after removal.

I'm not sure if that's the right part number but I did buy the genuine stuff from eBay and it was expensive. I'm sure there will be other stuff just as good and probably much cheaper but being an OEM guy (whenever I can) that's what I went for.

For vacuum any vacuum hose for £2-3 should be fine. But for diesel leak off hoses I found that cheap ones start dissolving and leaking very soon, I assume because of 7% biodiesel in the fuel these days. So in the end I bought 1m genuine hose on ebay. From dealer they only sell as roll of 5m around £160.

I ended up getting this:
https://www.ebay.co.uk/itm/VW-3-5mm-...72.m2749.l2649

Seems to have the same dimensions as the geniuine thing.

Will report on fit once it gets here.