[alexwhittemore]

I posted a thread in the N51 forum a couple days ago about leaking oil. On the advice of a local indy, I went and had the engine cleaned both from the top and from the bottom with the splash guard removed to get a clearer picture of the source. That was Monday, and I can now see clearly two things: there's oil dripping off the transmission housing (not off the drain plug area, anymore), and there's oil around the secondary air injection valve where it connects to the head. As well as the before-cat 02 sensor wire.

In addition to the obvious oil leaks, what prompted me to look into this in the first place was cat trouble codes 2CA9 and 2C78 (O2 sensor heater circuit and O2 sensor circuit no activity detected) - seems to indicate a shot O2 sensor. I also have 2A00 (secondary air injection system flow) - suggesting that the mass flow sensor for that system is shot, or else the valve is stuck or something.

So I guess my two questions are, 1) is this familiar to anyone, and 2) if I'm having emissions control hardware problems (O2 sensor and secondary air system), is repair covered under the SULEV 150k mile warranty in CA, even if the underlying problem is an oil leak of some kind?

[alexwhittemore]

Update: The O2 sensor and VCG were replaced under the extended emissions warranty. It's unclear how everything related, but all problems with the secondary air system seem also to be cleared up by the gasket replacement.

[kkasson]

The ECU monitors the secondary air system through the O2 sensors, so if the sensor was bad that's probably what caused the secondary air codes. The SAP pumps clean air into the exhaust at start up, so the computer expects to see lean readings from the O2 sensors while the pump is commanded on. If it doesn't see those lean readings from the O2 sensor then it thinks the pump must not be providing sufficient air to the exhaust, so it throws a low flow code. So if the sensor is bad it can fool it into thinking the pump isn't working.

Glad to hear it was all taken care of under warranty!

[alexwhittemore]

Originally Posted by kkasson

The ECU monitors the secondary air system through the O2 sensors, so if the sensor was bad that's probably what caused the secondary air codes. The SAP pumps clean air into the exhaust at start up, so the computer expects to see lean readings from the O2 sensors while the pump is commanded on. If it doesn't see those lean readings from the O2 sensor then it thinks the pump must not be providing sufficient air to the exhaust, so it throws a low flow code. So if the sensor is bad it can fool it into thinking the pump isn't working.

Glad to hear it was all taken care of under warranty!

That all would make plenty of sense - except that I think there's a dedicated mass flow sensor in the post-pump secondary air line before the valve? Could have sworn I saw that in the service manual.

Not that it still couldn't be the cause - it'd make sense to distrust one reading on the basis of the other. But I'm curious if the VCG can leak badly enough to alter airflow.

[kkasson]

Originally Posted by alexwhittemore

That all would make plenty of sense - except that I think there's a dedicated mass flow sensor in the post-pump secondary air line before the valve? Could have sworn I saw that in the service manual.

Not that it still couldn't be the cause - it'd make sense to distrust one reading on the basis of the other. But I'm curious if the VCG can leak badly enough to alter airflow.

I don't believe so, but I could be misremembering or they may have changed it at some point. But as far as I know, it's just the pump and intake/output hoses, and the valve on the head. The valve cover isn't directly connected with the SAP system, the valve is mounted on the side of the head and goes directly into the exhaust. On the E46 the valve was vacuum controlled, but the E46 M3 didn't have a vacuum line on the valve. It was controlled just by the SAP pressure. I think the E90 valve is the same, it just connects the air hose directly to the exhaust.

I'd guess what happened is the oil leaking from the VCG traveled up the O2 sensor wires and damaged the sensor. Or it may have even been coincidence that they went bad at the same time.

EDIT: Ah, so it looks like the E90 M3 does have a sensor on the SAP hose but the 328i doesn't.

[alexwhittemore]

Originally Posted by kkasson

I'd guess what happened is the oil leaking from the VCG traveled up the O2 sensor wires and damaged the sensor. Or it may have even been coincidence that they went bad at the same time.

EDIT: Ah, so it looks like the E90 M3 does have a sensor on the SAP hose but the 328i doesn't.

Interesting - maybe I was reading in the manual the general case which included the sensor in the assembly that'd be present for an M3. Weird that they'd include a sensor on the M3 if they decided they could get away without one on the cheaper cars.

The indy theory was coincidence, and I'm inclined to believe him. He thought that if they were related, oil maybe fouled the sensor. But the sensor body itself was dry (he very kindly put the car on the lift to check quickly, free of charge). The wires were soaked, but not all the way up to the connector and I'd be surprised if that was a direct cause of failure.

All in all, pleased it all was covered under warranty up here at 108k miles. Bringing it back in to the indy next week for a brake fluid flush it's long overdue for, I think they earned the business.