questforbalance

I have a 2002 C4S and have been getting PO430 DTC for about eight months. Each time it happens it occurs one day after filling with gas. Always the same code: PO430. I changed all the O2 sensors, but still got same code. Cleaned MAF sensor, changed air filter but still got code. I then put in some Cat 1 Catalytic converter cleaner and then got PO420 and PO430. Brought the car to Porsche dealer and they diagnosed that both cats were bad. They cleared codes and a few days later CEL came back on, but this time it only had PO430. Same as before. I then removed Bank 2 cat and cleaned it but PO430 still came back on. So I bought two new Fabspeed 200 cell Sport cats and put them in. But still getting PO430 DTC. WTF is going on? I bought a EVAP valve and will change that this weekend. I am slowly but surely rebuilding this car. Does anyone know what is the problem? How do I solve this problem? Any help would be greatly appreciated. HELP!!!

TSMacNeil

I'm new to Pcars, but familiar with BMW's.

You'd be wise to check the correct function of the ECT (coolant temperature sensor)
If it is sending a lean (engine/coolant cold) signal to the ECU, the ECU will dump fuel in to enrichen...and the cats will go crazy trying to handle it....and the o2 sensors will go even crazier.
(at least that's how it works in the "other" German cars)
BTW- excessively rich mixtures will kill the cats...so if the stealer was right, there's a clue that you're rich.

You should be able to confirm proper O2 sensor operations with a voltmeter too. When working correctly, they generally "dither' between .1 and .9 vdc...swinging back and forth like a metronome. Or, I guess most guys use a code-reader these days...showing my age a little here.

Ahsai

Do you have Durametric or any generic code reader that can display real-time O2 reading? Do you use Android phones?

C4911

It is possible that you have a small leak somewhere in the system causing that CEL. Sometimes replacing the gas cap is all it takes to fix, others require a smoke based leak test to correct.

questforbalance

This is great feedback and I appreciate it. The O2 sensors are about three months old so I doubt they are bad. Besides I would imagine that the Porsche dealership would have checked the O2 sensors as part of their diagnosis. They did a cold test to determine that the cats were bad. Strange thing is that I keep getting the PO430 code. The other side is fine. I changed the gas cap also and I still am getting the code. I also went back under the car to tighten up the exhaust bolts and to confirm that everything was seated correctly. I do not have a smoke machine unfortunately so I can't do a smoke test. The ECT (coolant temperature sensor) is something that I did not think about, however that was also replaced about six months ago when I had a transmission leak repaired after the mechanic broke the ECT. Makes me wonder if the one he put on is working properly. How do I check that? As far as a small leak somewhere, gee I wish I could find that. I figured I would replace the EVAP valve as I figured that the PO430 code keeps coming up a day after filling with gas. But then I have doubts about that too because it takes almost a tankful of gas before the ECU enters the read ready state. I have a Durametric and will try to post something soon. Maybe it will provide some clues that I cannot see. But it surprises me that Porsche did not identify anything except for bad cats. I plan on calling them and seeing if they are going to charge me again for having them look over the car again. I will keep everyone apprized. If anyone can think of anything else, PLEASE do provide your thoughts. Many thanks.

TSMacNeil

The sensors themselves shouldn't be expensive. I would check the connector on the ECT to make sure it's clean and tight. If the ECT output is missing ( bad sensor or bad connection) the ECU will default to a generic fuel mapping setting...which should be good enough to not kill cats or throw a code.
However, a false lean signal (or actual vacuum leak) will result in the ECU commanding a very rich mixture, and if the limits are reached, codes get thrown and cats can grenade.
The Bentley should cover checking the ECT, but I'm not at home to check it.

TSMacNeil

Sitting in a lobby having my 996 aligned and had another point.
If you can monitor the o2 sensor voltage outputs, they will tell you what the ECU is doing-
If the voltage is fairly steady towards 1vdc and not "dithering back and forth low/high/low/high....then the ECU is commanding a rich mixture.
It should only do that for real or perceived lean condition or a real or perceived "cold start"
That means if everything else is working, you have a post-MAF (unmeasured) vacuum leak or a bad ECT signal. You can track down vacuum leaks with some carb cleaner if a smoke machine isn't in the cards.

Ahsai

Since you have Durametric, you can check the coolant sensor readnig at start up and when moving to see if they give reasnoable values.

You can log the O2 sensor voltages on all 4 sensors on both banks. After engine has warmed up, at idle, precat sensors should swing between 0.2-0.8v about once a second. Post cat sensors should read about 0.7v almost steady most of the time. If you see the post cat reading kind of following the precat readings, your cats are shot. Now repeat the above but drive the car around. The pre cat should swing a few times a second when the post cat will still be around 0.7v most of the time. If you accelerate, both pre and post cat reading will hit ~0.9v almost instantly When you let off the gas quikly, both reading will go to 0v almost instantly.

Also, compare the post-cat readings on both cats. If it's not stable at 0.7v in bank 2 (P0430) most of the time, your bank2 cat is marginal. Should be obvious once you overlay the readings from both banks.

TSMacNeil

I don't know what this Durametric is, but I haz to have one.
Lol

morganabowen

I had a similar problem when I replaced my cats with the Speed Venture X pipe and high flow cats. After the installation, the codes were clear; however, about a week later, I had P0430 & P0420 codes pop up. I went back to my mechanic, and he checked and could not find anything wrong and we decided to replace the 02 sensors. Since then, no problems and it has been about 1200 miles since the installation of the Speed Venture equipment. In other words, you may need to run your car a few miles until everything settles. Good luck

TSMacNeil

FWIW- and I don't mean to suggest I know whats wrong with your car, by any means...

The testing of the ECT is found in Bentley 24-11.
Overview:
remove the plug from the sensor- with key "ON" should see the standard 5vdc reference voltage (Motronic uses a "bus voltage" of 5v)
If no 5vdc in the plug, check wires back to the ECU for continuity.

Sensor resistance tests: (with ohmmeter)
32F = 5-7k
68F= 2-3k
180F= .4-.8k

The ECT is a thermistor, which is to say a variable resistor based on temperature...the above values show the acceptable resistance for the sensor. (Replacement sensors should be about $20)

**after reviewing the original post- you might confirm that your fuel tank vent lines are clear and open (able to vent) I missed the "full tank" correlation.

BTW- Checking a cat is easy with a cheap digital thermometer from Home Depot:

Once warmed up:

Outlet temperature should be almost double the inlet temperature.
(as measured on the inlet and outlet of a cat)

Werd

questforbalance

Well, here is a quick update. Since it is cold as hell here in New Jersey and we have ice on the ground I decided to contact the Porsche Dealership who told me the original cats were bad. They agreed to look at the car for no charge. Um, that sounded like a fair deal. So I brought the car there. They checked the car and said that the Bank 2 cat (passenger side) is bad. They also said that since these are aftermarket cats, they cannot say with any certainty that I will not have a problem with the other side. What a PITA! So I called Fabspeed and they told me that I need to put an O2 extender on and that will fix the problem. Um, that sounds like a bandaid. I am thinking, now what? I asked if they checked out the health of the o2sensors, they said yes, and that everything else in the car is working fine. I am thinking I may change the o2 sensors as Larry did. Or maybe I will just drive it for a few thousand miles since the o2 sensors that are in there are about three or four months old and maybe 3,000 to 4,000 miles old. Any thoughts?

alpine003

Spend $10 and get the extenders. If they solve your problem, consider yourself lucky that a $10 fix would let you move on with life(especially on a Porsche).

FRUNKenstein

OK, this may be a stupid question, but I think my cats are bad and don't want to get in the same situation as the OP - replacing them and then still getting a CEL fault. The question - other than a rattling noise, is there a definitive test to tell if a catalytic converter is bad?

Ahsai

Yes, check out post #8 above. Oh, if you use an Android phone, I can tell you an even better and accuate way. Let me know.