Error code 491 492

Hi, I'm new to Pedro's Board and I appreciate the info from its members. My problem, my engine light on my 05 Boxter comes on every 3 to 4 k . Error code 491 492, Dealer in Raleigh NC found small amount of oil that has harden coming out of the manifold on one side of engine. They tell me that it's possible that oil leaking into some secondary air passage that supply air to the Catalytic converter need to be cleaned out. They quoted about $400 just to drop manifold and wasn't sure on how long to clean out air passage. Not sure where oil is coming from possible a leaky valve? I hate to spend a lot of $ only to find the engine light will continue to come on after they clean the air passages....any one have similar problem ..

My info is:

P0491: Factory Fault Code 591 - Fan output stage 3 Open circuit, below limit, or above limit

P0492: Secondary air injection system, Bank 2 Below limit.

Looks like something related to the secondary air injection system. The errors are rare in my experience.

I did a search and found this:


P0491 Secondary Air Injection System, Bank 1 - Insufficient Flow
P0492 Secondary Air Injection System, Bank 2 - Insufficient Flow

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 Check the fuse and relay to start. Also, make sure the secondary air is plugged in. Sometimes when work is done on the car the tech remove the pump and then forgets to plug it back in when they put in back together.

The air injection ports can get blocked but that is most often found in the air cooled engines (993) and arises from when the valve stems/guides/seals wear and allow oil to pass which can form carbon and block the air injection ports into the engine intake.

Most often with the newer cars the water cooled engines it is a switch or a hose or a connection that is the cause of a secondary air injection related problem. In the highlight paragraph above, note any blockage or restriction causes are down on the list of possible explanations.

I note both banks have faults, so the failure is I would guess a common one to both banks. Hard to believe oil leaking into both banks enough to block all or enough of the secondary air injection ports. Does the engine smoke at start often? (It can smoke once in a while which is normal. I'm looking for this smoking at start to appear too often. How often is too often? Well, one rule of thumb is when it happens if you can remember when it last happened, that's too often...) Does the engine smoke when warm when you step down hard on the gas pedal? Or when you lift off the gas pedal? What is the oil consumption? Heavy? Do you run the oil level too high? Over the max line?

Absent any signs of smoking which would be, could be, present if the oil was getting past the valve stems/guides/seals I'd have to say in my opinion, let me make this clear, my layman's opinion, the problem is not due to some secondary air injection ports being blocked.

However, as I mentioned above, I'm not a mechanic. So, I guess it boils down to if you trust the place where you are taking the car.

Those two codes are:
P0491 Secondary Air Injection System (bank 1)
P0492 Secondary Air Injection System (bank 2)

The most likely is that a vacuum hose has come loose but less likely is that one of the changeover valves is failing or that there is a problem with the wiring (usually caused by rodents). Did you have any work done in the area of the back right of the engine compartment at some point?

Edited 1 time(s). Last edit at 09/08/2013 04:16PM by Laz. (view changes)