Han Solo

I'm getting check engine light and my Durametric shows - P0421 Bank one catalyst warm-up efficiency below threshold. I'll clear it but it will come back after 20-30 miles. What's the prognosis doctor? Oh, this is on my '07 Cayman S with 58,000 miles.

Macster

I'm away from my references but I can recall this one from memory (thanks to my 02 Boxster that emits a P0430 every once in awhile..)

If the eror code is accompanied by error codes related to aging sensors replace the sensors indicated by the error codes, clear the error codes, and resume driving the car. If the code comes back the converter is worn out (unable to store oxygen) or perhaps has suffered some internal mechanical failure that has affected its operation.

Converters are warrantied by federal law for IIRC 7 years and 80K miles -- this should be covered in one of the books that came with the car -- so you should get the car to a dealer for 1) confirmation the converters are covered; and 2) get the bad one replaced.

I have nursed my Boxster's sub-par converter for years now running a top tier (mostly Shell, but Chevron works too) gas and buying from a busy station, and once every two years (but not always, sometimes I get lazy or the car is just behaving ok... switching away from 'supermarket' gas to a name brand gasoline really keeps the eror code at bay) before an emissions test running a bottle or two of Techron through the gas tank.

Keep the plugs reasonably fresh -- replace every 60K miles -- replace engine air filter every so often, avoid overfilling the engine with oil, and then drive the car.

Oh, I found pushing the engine a bit harder -- nothing harsh just rev the engine a bit higher, use a bit more throttle -- seems to help forestall the CEL and error code. It still comes on though almost always in cooler weather.

Sincerely,

Macster.

BGB Motorsports

Does the car have stock exhaust manifolds? This is typical for cars that have race headers but you would get it for both banks 1 & 2. I could be wrong, but I would think that the ECU thinks that the cat is going bad.

It's running the same process that it runs to check for cats at warmup. However, I have seen faulty O2 sensors be the cause of this. But your fault would most likely be in conjunction with an O2 sensor fault. It's probably the cat. I would try and find a junkyard set of cats or maybe call LA Dismantler or something like that.

Han Solo

Update - I swopped the two post-cat O2 sensors and it hasn't thrown a code yet.

Macster

Give it time. You just have *not* driven the car enough/the right way for the DME to complete its tests of the readiness monitors, the testing of the vital sensor/control systems in the car and their operation.

Converters of course being one of the top 3.

Sincerely,

Macster.

Han Solo

What was interesting was the codes started almost immediately after changing the clutch and flywheel (that's a whole 'nother story). We disconnect the exhaust after the cats and drop the whole assembly. Makes me wonder if shaking those components about didn't loosen up some junk to cause the code.

Macster

There might be some connection. The converters live in a horrific environment when working. They are of course designed for this, but the heat and cold and vibration takes its toll.

The exhaust system when removed needs to be treated like glass. Before the converters became part of the exhaust manifold the exhaust manifolds were battleship tough.

The exhaust manifolds with built in converter are still are quite tough or we would have more failures but the insides of the conventer? Not so tough.

I think I hear a metallic buzz coming from the occasionally bad converter on my car. There has never been any reason to remove that converter but if it ever comes off I'll be the first to give it a rattle test. I suspect the unit has suffered a mechanical failure. I note the other side is working just fine and both have covered the same number of miles subjected to nearly equal doses of exhaust gases.

Sincerely,

Macster.

Muzzy

I have exactly the same problem and had all 4 sensors replaced. Everything was fine until about a month went past and the error code came back. It now comes back on every day or so. Also, I can hear a metal shaking sound when I rev the car slightly harder.

I'm starting to think I have a cat that is going bad...?

If this is the case, which cat would be Bank 1?

Han Solo

Passenger side. Cylinders 1-3.

Muzzy

Is that passenger side in US? So would be my drivers side (I'm in England)....