shocks

Hey Folks,

Looking for some help understanding a CEL issue on my P&J 996tt I've been hitting.

Symptoms, small whine for < 10sec at start from cold, CEL would be thrown up on short journeys <12miles in commute type traffic (always low speed when CEL comes on).

Had the car in at indy and it's been narrowed down to P0491 / P0492, in investigating this the following has been done :

Pre P0491/P0492 - was throwing up
(1) MAF replaced

Post and finally narrowed to P0491/0492

(2) Electrical Secondary air valve replaced

(3) Air pump checked - confirmed working

(4) Vacuum checked through system and present

To progress Indy would like to remove engine to replace Overrun recirculation valves and/or Electrical switch over valve

So here are my questions :

- Is it necessary to do an engine out to complete this (had a look at 996 Turbo vacuum system diagram which isn't clear nor is the 491/492 troubleshooting flow mentioning engine out !)

- Is there anything else that should be checked that may be causing this ?

- Planning to replace the DVs while this work is being done ?

- Any recommendations on other preventative maintenance while undertaking this work ?

Many Thanks
S

Kevin

Is the whine the electric air pump> yes or no... They fail. It might be running but not supplying the CFM required.

You do NOT need to drop the engine to replace the Cutoff/bypass valves.

You might need to find a different mechanic or take to a Dealer for service.

JG 996T

My car threw same codes about a month ago - dealer diagnosed and fixed under CPO. If I remember correctly, a valve was leaking air, and they replaced it, no big deal.

Kev's probably right, you might want to take it to the dealer.

Macster

My references aren't handy but it reads like most of the causes have been eliminated.

Those errors (working from memory) indicate that the DME is not seeing the expected readings from the sensors which should signal extra oxygen is present.

If the secondary air injection pump runs when it should, if the thing puts out air, if the secondary air injection control valves work and when they should, then all I can think of is the problem is with hoses.

If both errors being present isn't an artifact of the system -- sometimes the DME will set errors for both banks even though only one bank has been identified as having a problem -- the failure is a common failure so the line from the pump to where the valving is and any common lines afterwards would be a good place to look.

If something is amiss whether the engine has to come out to address it I can't say. The tech should know and either you trust him in this regard or you don't.

If the engine has to come out what else you do is up to you. Certainly the tech should note anything that obviously needs attention, any fluid leaks, any sign the clutch needs attention. At this time it would be a good idea to check the dual mass feature of the FW, too.

The serpentine belt can be checked for any signs it is rubbing, which is a sign an accessory drive has excessive bearing play. All of the accessory drives can be checked for any signs of play. The idler roller/tensioner roller bearings can be checked at the same time.

I assume the clutch's boost is working ok that the accumulator holds boost after the engine has been shut off and left off awhile? If not then an accum. is called for and while you're there a clutch slave cylinder might not be a bad idea. (Shortly after the accum failed on my Turbo the slave cylinder failed and both were replaced at the same time.)

There is a test to determine if the DV's are working ok. If the tests find any issues then of course the DV's get replaced. If they are found to be ok if you want to replace them as a preventative measure, it is up to you.

In fact, to state the obvious it is up to you what else is done. I prefer to let the car/engine tell me what it needs doing before I have something done, like the clutch, DV's, coils, water pumps, and those sorts of items; but you can have done whatever your budget allows for.

Sincerely,

Macster.

JG 996T

From www.Renntech.org

Possible cause of fault
- Electrical fault in power supply or line between relay and secondary air injection pump
- Secondary air injection pump relay mechanically faulty
- Mechanical fault in electrical secondary air valve
- Pneumatic secondary air valve faulty/sluggish
- Electrical fault in secondary air injection pump
- Mechanical fault in secondary air injection pump or secondary air injection pump blocked
- Vacuum system leaking
- Air hose to secondary air injection pump slipped off or constricted

Macster

Just happen to be a dealer today killing time while my Turbo's getting serviced. I asked about the errors and based on the brief err briefing I got JG 996T's post covers the subject very well.

The tech told me that the pump can be changed with the engine in the car but depending on what else is wrong because things are so tight the engine may have to come out of the car. It all depends upon what's wrong and where.

This should be an incentive to as best one can eliminate the easy to get at possibilities.

Oh, one tech suggested the O2 sensors could be weak and slow to react to the extra air injected by a perfectly functioning seconary air injection system. I didn't see any reference to the sensors in the details posted by JG 996T but it is worth considering.

With the proper diagnostics computer -- and in some cases even with just a feature rich over the counter OBD2 scan tool/code reader (for instance my 'ancient' Actron provides me with the ability to run some sensor tests for my Turbo -- various O2 sensor tests can be done and bad sensors possibly id'd. If the tests can be run and if one or both sensors are flagged as bad or even questionable it is cheaper to replace these sensors than it is to possibly drop the engine. If the sensors are deemed in need of replacement then afterwards the error codes are cleared and the car driven and used to see if any more secondary air injection errors occur.

Sincerely,

Macster.

Macster

Just an update. I asked and got an 8 page print out of the P0491/P0492 section from the Turbo Obd Diagnostics manual. O2 sensors are not listed as a possible cause of the errors.

To the OP: Send me a PM with your email address and when I can -- I'm out of the office today and I may be out until Saturday -- I'll make a PDF of these pages and send the PDF to you.

Sincerely,

Macster.

shocks

Guys thanks very much for the replies !

Macster - YHM ! Defo interesting as on checking on the codes I missed that there is a P0175 for Oxygen Sensing adatpion - idle range on bank 2.

Thinking aloud I wonder if P0175 could be the cause and the mask of P0491 being triggered ?

Notwithstanding the still there whine when start from cold, which is why we were chasing down the vac system and SAI setup.

Macster

Well, as I mentioned while one tech said the sensors could be suspect, another disagreed. (This highlights a problem with asking these questions cold and that is the question comes out of the blue, with nothing more to go than in this case two error codes and the tech unable to speak to the owner directly, and knowing nothing of the car's history, condition, servicing, etc. So, I always give the techs the benefit of the doubt when I get what appears to be conflicting info.)

Anyhow, if there's a P0175 error present this signals at least one #1 sensor (on bank #2 IIRC) is questionable...

(P0175 - Oxygen Sensing Adaptation, Idle Range, Bank 2 - Below Limit)

As before I'm away from my references but give me a chance to look this up tomorrow (I return to work Wednesday, just heard from my manager) and I'll respond with what you can do to identify the cause of the P0175 error.

Until you've had a chance to delve into this further, I would not replace both or even one of the #1 sensors based on the presence of the code but I would run whatever sensor tests I could to if a sensor is bad to give the DME every chance to flag it as bad.

If it proves that both or even one sensor is bad I think it is clear that the sensors get replaced before dropping the engine to deal with a suspected secondary air injection system problem.

If the sensors are found bad and replaced the error codes must be cleared and the car driven some more. If the air injection system has its own fault this will be caught and the check engine light turned on and the codes will point the finger at the secondary air injection system.

Sincerely,

Macster.

daytrip00

I got these two codes. It was a leaking diverter valve (#2 in the above picture). You said you checked for vacuum leaks, so that might not be it, but from my research, the vast majority of the time, those codes come from a failed diverter valve. (JG 996T, it seems, had the same issue).

Kevinmacd

Yup, bad divertor valves. Replaced mine with Champion, and has been fine ever since. Before getting those codes, the air pump would come on on cold startup, and make noise that was not usual, then the codes popped up a little time after. I chose to get the Champions because the Bosch are failure prone.

Macster

P0491 PDF sent to the email address you provided in a PM.

Sincerely,

Macster.

tvurt

I had the same codes from a cracked "y" fitting that is not on this picture but is made of hard plastic and sits right where the #3 is. Found it with a boost test from the turbos and replaced it in about 10 mins with a nut driver. $47.

Do a boost test from the turbos and get some soap .. . . .

Angelus

Hi Shocks, when did you start noticing the whine? Does the car perform different?

As you've got an X50, is there any differences in the vacumm system to the normal Turbo?

If the engine does come out, are you getting the coolant pipes welded?

Lee.