CEL Help!

[mjp911]

I have a CEL problem that is driving me nuts. Car is indicating codes P0136 and P0140 (P0136 porsche fault code 17 - o2 sensor aging behind cat bank 1;

P0140 porsche fault code 12 - o2 sensor behind cat conv bank 1) When I reset CEL, it stays off for a while, but then comes back. It usually comes back while traveling under light acceleration/coasting - sometimes within a few minutes of being restarted (eg after stopping for gas). I had all the O2 sensors replaced - same problem. One of the aftermarket mufflers from the PO was making strange sounds and blew out its packing so I replaced both of them too - still same problem. Funny thing is the CEL won't come on at the track or when driving briskly - only under light acceleration/coasting. Any ideas would be greatly appreciated. Also, if anyone has an electrical diagram for the O2 sensors etc, that would be appreciated - I suspect this is an electrical problem - maybe the signal or other wire shorting out. [/size]

[Loren]

P0136 Oxygen Sensor After TWC, Bank 1 – Signal Implausible

Possible fault cause

- Short circuit to ground in signal wire

- Intercore short circuit

P0140 Oxygen Sensor After TWC, Bank 1 – Open Circuit

Possible fault cause

- Open circuit in signal wire or ground wire of oxygen sensor

- Oxygen sensor heating faulty

Either the wiring is damaged or that oxygen sensor is bad.

[mjp911]

Thanks Loren. I had all the sensors replaced so I think it is an electrical problem with one of the wires, as you note.

[RR GT3]

Good morning all - I have virtually the same problem. The exhaust system on my car is FabSpeed headers, cats, mufflers. Just replaced the cats under warranty. Replaced the 4 O2 sensors and checked wiring. Was able to avoid CEL long enough to pass NJ emissions inspection. Spent almost 8 hours on track over two days at the Glen with no problem. Spent 30 minutes in traffic today, just like mjp911, and on comes the CEL. The computer indicates O2 sensors which can be reset.

My next thought is that the system is not hot enough and I'm tempted to wrap the headers just to see. Comment?

[Loren]

Good morning all - I have virtually the same problem. The exhaust system on my car is FabSpeed headers, cats, mufflers. Just replaced the cats under warranty. Replaced the 4 O2 sensors and checked wiring. Was able to avoid CEL long enough to pass NJ emissions inspection. Spent almost 8 hours on track over two days at the Glen with no problem. Spent 30 minutes in traffic today, just like mjp911, and on comes the CEL. The computer indicates O2 sensors which can be reset.

My next thought is that the system is not hot enough and I'm tempted to wrap the headers just to see. Comment?

What are your fault codes?

[RR GT3]

I knew that would be asked as soon as I wrote this. I don't remember well enough to say for sure. I think maybe I'll take a "smoke" break and go check. Be back soon. Thanks.

[RR GT3]

Well the "break" took longer than expected because the computer was dead. The codes are:

PO430 Porsche fault code 45 - catalytic converter efficiency bank 2

PO420 Porsche fault code 40 - catalytic converter efficiency bank 1

Thanks,

Warren

[Loren]

P0420 40 TWC conversion, bank 1 - above limit

Possible fault cause

- Oxygen sensor ahead of and after TWC exchanged

- Valve lift fault

- Aged oxygen sensor after TWC

- TWC faulty

P0430 45 TWC Conversion, Bank 2 - Above Limit

Possible fault cause

- Oxygen sensor ahead of and after TWC exchanged

- Valve lift fault

- Aged oxygen sensor after TWC

- TWC faulty

What O2 sensors did you buy? Many aftermarket sensors give errors. If this is the case you will need Bosch or Porsche O2 sensors.

[RR GT3]

That was a better question than you might think. I checked my invoice and there are no sensors on it. I cannot imagine my shop missing that cost but I need to check. I was sure we put new ones in but it seems only the cats were replaced. I'll get back to you. Thanks, Warren