Carpoof

My '05 W12 D3 just started giving codes P0491 & P0492 which is secondary air injection insufficient flow. The engine was replaced about 5,000 miles ago and everything was disconnected, not sure if something got disconnected and not hooked back up or what. It runs ok other than sometimes when I floor it from a stop it will hesitate for a second and then ramp up in power (as if the knock sensors or traction control kicked in hard). It also lacks in high RPM power. The W12 has 4 banks of cylinders so I am not even sure where to start looking. Any advice is greatly appreciated! Thank you!

Jack88

I'd follow the codes, first check for reasons the air injection may not be functioning properly. Pinched or degrading wires, for example.

MP4.2+6.0

Run VCDS, report back on which banks, any results from self test diagnostics like running up the (two) air pumps, etc. Typically the codes are by specific bank. If this is a generic code reader, get the right tool for starters.

Carpoof

Thanks for the help guys! I only have a Carista scanner, it shows those codes and says bank 1 and bank 2, but I know there are 4 banks. I'm assuming it is one side of the engine? I can't afford the proper scanner to test the pumps individually. I was hoping I could just look at the pumps and associated hoses to find something obvious. Can anybody point me to where the pump / vacuum hoses would be for banks 1 & 2?

Jack88

The proper scanner to which he refers is $200, and would pay for itself the first time it prevented the old diagnose by replacing parts technique. Many would say if you can't afford the $200 tool, you probably haven't any business in a W12, but all I can say is that you may in for a rough time trying to keep one up on a budget. It seems that although there are 4 rows of cylinders, it still designates 2 banks.

Carpoof

Thanks for that info, I understand about the W12 being expensive to maintain, I just figured this was something simple enough to figure out mechanically.

Giovanni Giovino 6.0+6.0TT

Hello Carpoof,
This may help you understand the W12, the cylinders are as jack stated bank 1 and 2, the exhaust manifolds are labeled banks 1 through 4, also being you had the engine out I would be checking for connections that may have come loose, follow the combo valves on the front of the engine to the secondary air pumps, a loose air hose or cracked for that matter would cause the "secondary air injection insufficient flow " , if you had the proper Ross-Tech cable you would then be sure of actual code or fault, also then you would be able to test said secondary air pumps for running and flow.

.

richard-tx

It may help to view the W12 as two 6 cylinder engines with a common crank. If I recall corrrectly, each ecu handles 6 cylinders.

MP4.2+6.0

For the first hour + of added time with the insufficient tool...what you can do is apply power to the relevant pump. Banks 1 and 2 mean North America/Continental Europe passenger side of car + motor as you face it from front of car. Would be two minutes w/ VCDS in diagnostic mode, but a bunch more time otherwise. Take off (U.S.) driver's side fog light grill and reach in there to pump electrical connectors. May have to remove belly pan too; yet more time and hassle. If you own older Audis, getting to point you need to remove belly pan easily is a "when," not an "if." But I don't recall which pump is which (two pumps in an overall assembly, one for each side), so you will need to trace the output air lines to each side of motor/combi valves up by the cylinder head area to find the correct pump. Along the way you need basic familiarity with removing fog light grille and typical Audi wiring connectors without breaking them. Hints: use flat medium blade screwdriver to lever holding tabs slightly inward on foglight grill while pulling outward. Conversely, basically never use a screwdriver on an Audi wiring connector lock tab or you will break it 95%+ of time on a heat soaked 10 year old car, let alone a lot younger.

Fashion a set of wire jumpers with flat blade female terminals on ends of the two conductors and attach to pump. Power with 12V nominal and see if it spins up. Sounds like a small vacuum cleaner, since that is basically what it is. If one does not spin up, that's your suspect. If unsure of your connector or diagnostics, repeat on other pump nearby, which should then spin up. If the pumps do spin up, now you need to look at valves and hoses and such, skipping over low percentage areas like wiring harness, ECU, etc. For those you also need to get into W12 documentation. A guess is both pumps are off one fuse (and thus either running discounts that issue) and that pump control is off one ECU rather than both. The ECU's are divided up for core fuel and timing stuff IIRC, but only one controls for a fair number of other functions. Again, pumps, hoses and valves are probably 90% plus of action/problems here (and vacuum hoses on ones that use them; W12 does not) , so I am going light on the electronic side. On mine, I ended with a driver's side bad pump that had ingested water, apparently when the drain hose from the engine air box above (where both pumps get their air supply) got kinked and pump ate water over time. Narrowly applies to mine, but moral of that story if a pump issue and any water involved is to look further and isolate cause to avoid buying yet another pricy pump in future. Also to know, if you know W12 engine sound at slightly elevated idle in general, you can also hear the air pumps at cold start up. Best to listen with A/C off/in Econ mode to avoid added radiator fan noise. You will hear that pump/somewhat faint vacuum cleaner sound even over sound of engine even if only one pump is working. But hard to know acoustically if you are hearing both, or just one. One of the things that actually faked me out until I got into individual pump testing and I first thought it was the combo valve. But if you hear none at all, then suspect it may be more basic electrical supply. They only run at cold start up, so best to test for basic run sound after sitting overnight. You can also try to feel either one for running vibration by putting your hand right on it (through the foglight grille opening or otherwise), but you may have as short as 30 seconds after a cold start. Again, why the VCDS diagnostic spin up of these is oh so much easier.

As perhaps you can tell, I don't think much of Carista for stuff like this. Funny how in the pitch and feel good basic coding change stuff the harder diagnostics don't get highlighted. SAI is among the most challenging systems in Audis to pin down; fortunately Audi's aren't as burdened with fuel vapor/evaporative system issues like some other marques that can be yet more fleeting to pin down. Regard Carista as a lightweight typical app to set a few things and read some basic P codes. But underpowered when it matters for older Audis with more issues, get into self run diagnostics, etc. It will be your knuckles, back, frustration level and not unlikely wallet that end up paying more than the difference as a continuing owner.

Carpoof

THANK YOU GUYS FOR THE HELP! Sorry for the slow response, I've been pretty busy lately. This definitely gives me a starting point. My lower fog light grille actually got broken out when I hit a raccoon a couple of days ago so I guess that's one less thing to remove, lol. Anyway, I am going to try all of these suggestions. I have noticed a high pitched vacuum type sound when I first start the car in the morning that I never heard before, but not sure if that's it or not.