autobahnNY

I had my check engine light checked out. It came out as: catalyst efficiency below threshold, bank #2 (Code 0431). Any ideas what's actually wrong? I reset the ECU by disconnecting the battery. So far the car is running strong and check engine light hasn't return. Thanks.

85percent

bad oxygen sensor on your exaust. it's telling your ECU that something's wrong with exaust output. if you don't replace the sensor, the check engine light will most likely return within a few days..

autobahnNY

Exactly..I received some info from Renntech org. Basically saying the same. I reset the ECU by disconnecting the battery. The car has been running strong. If the light returns, the cat should be replaced according to the OBD II manual.

deliriousga

You need one of these http://www.autotap.com/products.html if you're going to be doing your own OBDII diagnostics. It has more than paid for itself ($180). It reads the entire system, plugs into a laptop or PDA (you choose) and records everything. It will also clear out your error codes with a click of the mouse.

I had a stalling problem in one of the other cars so I plugged the AutoTap in and recorded my trip to the office. I could read the mixtures and sensors as each stall happened when I played it back later. Helped me figure out it was a $3 tube to the PVC valve that was causing a vacuum leak.

autobahnNY

Thanks. That will definitely be a future purchase.

jumper5836

I have this problem now. I first noticed that at warm idle. Its rpm is 100 lower then normal. Then there is a rattle.
Engine light came on 1 week later, so I brought it in and it is the catalytic converter.

deliriousga

How many miles do you have on it? Just wondering when to start listening.

Did they say if the rattle you hear is the internal scrubbers coming loose and rolling around? That's what happened with my Jeep and if one of those babys goes down the pipe it can clog up the works and the engine dies. Like a potato in the tail pipe.

autobahnNY

I didn't get any of those symptoms. The car is running great, probably a faulty code. I'm keeping a close eye on it though. Thanks for the input.

85percent

a bad oxygen sensor will typically drop your RPMs a little lower than usual, because since the ECU is reading bad signals from the faulty sensor, it directly effects the rate of your RPM's. which also may cause your engine to stall if it gets bad enough... as for the rattling, i'm thinking something was loose in your cat, and probably had something to do with the bad o2 sensor since its in the same area...

i wouldn't just keep an eye on it, i'd replace that sensor.. its sort of important for your ECU to get correct readings..

autobahnNY

My car is running fine. Faulty codes are thrown in error at times. That's why the OBD II manual says reset and if it comes back on then you have a problem.

85percent

90% chance it will come back... so i'm assuming it will.. if so, yea replace it..

jumper5836

I am thinking something is lose in the cat also, not a common thing though.
I have 2 wait 2 weeks for a service appointment. Damn Cayenes have ruined Porsche service.

GaryN

Hi jumper5836,
I had similar rattle only at idle, it was the heat-shield that covers the CAT (the one screw had vibrated off). As this is such a common problem with 996's and 986's the OPC's use a new type of bolt and nut/washer system. I had mine done last weekend (I should have taken a photo of the new bolt & nut system they use now for you guys).
The lower rev's at idle (believe it or not...mine also did that...) was the MAF (Mass Airflow Sensor) sensor (it's next to the airbox on-top of the motor (piece of cake to change, took 20 minutes - you need a TORX 25 socket).

Cheers
Gary

autobahnNY

Update: Two weeks and well over 300 miles of driving and no check engine light. Still running strong.