su20

I've been reading all the posts I can on this code, but can't decide where the most likely root cause is, I hope you guys can help...

2002 C4S 47k miles

My CEL lit up in late June, so I pulled the code with my Vag-Com (PC based software for Audi's, so it only can access the generic OBD codes on my 996, but it does allow data logging). It was P0174 - Fuel Trim; Bank 2: System Too Lean. I reset it, and started reading on the forum. I never noticed any problems with how the car was running, either at idle or under load.

In mid July it lit up again, by the time I got to checking it again, I had two codes:

P0174 - Fuel Trim; Bank 2: System Too Lean

P0507 - Idle Control System RPM: Higher than Expected.

I cleared the codes again, warmed it up, and tried to log MAF, short term fuel trims, and long term fuel trims, but I'm not sure I was using the logging function properly so I don't trust the data logs from this first check. I did notice, though, that the LTFT's were different, 6.3% rich on bank 1, and something like 3% on bank 2. I'm not sure if the difference points in any way to an O2 sensor rather than an MAF. But I found a thread on cleaning the MAF, so I got some electronics cleaner and did that. I ran it for about 10 minutes, re-checked the LTFT's and they were 3.1% bank 1 and 0.8% bank 2.

I drove locally for about 3 weeks, and the CEL has re-appeared, this time a new variation:

P0174 - Fuel Trim; Bank 2: System Too Lean

P0171 - Fuel Trim; Bank 1: System Too Lean

So I cleared them, warmed it up, and logged some more data:

I've seen Loren post a couple times that if you check the MAF readings at idle and at 2500 rpm, you can tell if it's working. In one post I think he put the values for both (actually idle and no load 3000 rpm) but the ranges are in kg/h. My logging software shows g/s. The values I got, averaging a group of readings:

741 RPM, 3.33 g/s

2540 RPM, 11.49 g/s

Assuming g/s is grams per second, these convert to 12 kg/h and 41.3 kg/h, which is just on the bottom edge of the 12-24 range at idle and below the 50-80 range at 3000 RPM (although I measured at 2500 RPM). Could this be the problem?

Also my LTFT's have now adapted to 2.3% on bank 1 and 1.6% on bank 2, much closer together.

I've done my best to visually check for intake air leaks, but I don't know if there is an easier way to do a more thorough check without special equipment. And I don't know how to get the oil fill tube off the engine block to check it, if that's even necessary.

I'm looking for advice on what to do next. Clearly I'm trying NOT to take it to a dealer for fear they'll just start replacing things. My dealer wants $308 for each of the four O2 sensors (Pelican has them for about $125). I could take it to them for a diagnostic, they'd do that and it might be worth it, then just replace whatever needs it myself.

I can log additional info if it would be useful.

I appreciate any advice you guys have.

This is good info. I am running Pilot Sports on my C4S right now, and the rears are wearing extremely quickly. My driving style is similar to yours, so I may try this option next.

I just checked the Michelin site, and Pilot Sport A/S Plus in the following configuration is withing the 2% tolerance:

(sorry I can't get this formatted into columns... tire size, then Michelin part number, then diameter, then revolutions/mile. Difference is 1.3%.)

Mich part dia rev/m

225/40ZR18/XL 21977 25.08 829

285/30ZR18/XL 20061 24.76 840

difference -1.3% 1.3%

Just wanted to close the loop here.... I replaced the switch, and [so far] everything is fine. If you want to do it yourself it's an easy swap, just do a search for the thread titled "Driver Side Vent Removal" and you'll see a nice diagram and instructions that Loren posted, makes it easy.

Thanks for the help, everyone. :renntech:

We'll be paying that kind of tax soon!

Just ordered the switch, $113. Should make you feel a bit better. :D

The bi-xenons have a special ballast attached to the back of your headlight assembly. Regular bulbs will not have this. Sound like the ballast may be going bad, similar to a 2x4 troffer light in a typical office ceiling space. I would get it tested by a an electrical shop.

You could be right, but I'll probably try the switch first. Unless I can find a suitable electrical shop near me, and I can't think of any off the top of my head. Sounds like enough people have had to replace the switch that I'll take the gamble.

Thanks, John... I better order one before the almighty dollar starts giving up its recent gains against the euro! Not sure why you guys get hammered over there, do you get taxed as heavily on parts as on the cars themselves?

...I would have to say it's like the flourescents sometimes they just don't hit right and do not light the first time. I'd have to say you don't have much to worry about...

Thanks. I wasn't too worried until they went dark while I was moving! :drive: Have to fix that, too much at stake.

Recently (now that it has gotten cold, not sure that's relevant), I've had a couple instances where I turned on my lights and they failed to come on. A couple times cycling the switch resolved the issue, but then when I was driving one dark night (in my rural, deer infested area of PA) I flicked to high beams and all lights went out! Luckily I pulled on the fogs and it was enough to get me stopped without driving into the ditch...

I've looked around on the site, and haven't seen this exact problem, but the related ones seem to point to the light switch. Is this so obvious to those of you in the know that I should just order the switch, or is there something else I should check?

'02 C4S with Bi-Xenons, both work normally (color, intensity, leveling, etc.) when they're working...

Thanks for any insight.

Hi,

You should try and get a 3-way kit from any manufacturer with a 3 way crossover. Most of the 3-way kits I've seen come with 6.25", which may be too big to fit.

Alternatively, use a 2-way kit with a 5.25" mid bass driver and a tweeter and use the in dash receptacle just for the tweeter.

I used two Alpine PDX4.150, totalling 8 channels. I bridged two of them for the sub and used the other 6 for everything else: two for the rears and four for the fronts.

What you should NOT ever do is wire different sized speakers in parallel. The results are guaranteed to be absolutely horrible: different sized speakers will have completely different frequency responses, in some frequencies you will have unnatural boosts, in others sound will seem to disappear into a hole. Do not do that, your amps will not complain, but your ears will.

Check my install in the 996TT DIY section of this site.

Have fun!

Obrigado, Luis! Great advice. I checked out your system, it rocks.... you've got some serious scratch tied up in that, must sound awesome.

Thanks again,

Todd

I'm planning to replace the Bose "upgraded" CDR-220, amp, and speakers in my '02 C4S in stages, and have been reading everything I can find on the forum - lots of great advice. I'm planning on decent speakers and probably a 5-channel amp (5th channel for subwoofer so I'll only have one amp). What is confusing me is how to hook up 6 speakers to 4 channels, in particular... what is the best way to connect the four front speakers to the front channel of the amp?

I think there are two options as far as I can tell:

- Use a crossover to split the channel between the dash and the door, using the door speakers as mid-bass speakers. Would this keep the load at 4 ohms?

- Wire the dash speakers and door speakers in parallel, which would effectively make the front channel 2 ohm

If I did the latter, I believe most amps are 2 ohm stable and this would actually give me a bit of a boost in power to the front speakers, but would this cause a problem if the rear panel speakers were hooked up as a 4 ohm load? I suppose I could add resistors to the front circuit to bring it back to 4 ohm.

If I did the former, would I have to buy additional crossovers and where would I install those?

I appreciate any advice!

Congratulations! It's a beautiful car. Enjoy it... from behind the wheel... every chance you get. This is when you will really appreciate this car. Welcome to the madness!

Shall we start talking about mods? :clapping:

http://www.renntech.org/forums/index.php?showtopic=7592

Loren, if there is a hall of fame for 'giving back to porsche owners', you're in it man! don't know what drives you, but you're awesome!

Audi got this one right.... effect is the same, when you turn on the rear fog, only the left rear fog lights (driver side in the US). But both rear lights have a separate bulb socket for a fog light, they just omit the bulb from the right! I swapped the bulb over, and sure enough the right side lit. Clever.

Too bad porsche didn't do it this way, would save some work.

I don't think the database is a good idea...

A database to track failure info will only keep those who eagerly consult it from driving their cars, for fear of the same thing happening to them. If 1 in 1000 have a certain transmission failure at 31,000 miles, and another 1 in 2000 have a sunroof failure at 26,000 miles, [etc.] what are you going to do with that info?

Quit worrying and drive it. When it breaks, fix it. When you're tired of fixing it, buy a civic.

Thanks for the help, I wanted to be sure not to break anything.

I'm going to do a couple DIY mods at the same time - trim my remote unlock wire to 130mm, and install a hardwired garage door opener. The only instructions I can find to remove the a-pillar trim are for a cab, where you remove the screws around the base of the sun visor. C4S trim runs in one piece from the dashboard all along the top of the door to the seat belt trim on the B-pillar (and doesn't come anywhere near the sun visor base, as far as I can tell). Not sure if this is the same for all 996 coupes, or only certain ones.

Can anyone tell me how to remove this?

:renntech: (I know I'm sucking up!)

What kind of tires are you using? That plays a much bigger part than any electronic nanny or awesome drive train you have. If you don't have snow tires on, your not going anywhere.

I may try BLIZZAK tires when the Pirelli's wear out.

I wouldn't recommend that... Unless you're only driving in extreme cold, your Blizzaks will wear out extremely quickly. Winter tires, in addition to having tread patterns optimized to snow and ice, are made of compounds that remain compliant in cold temps. When it's warm, they wear like silly putty. Summer tires are optimized for warm temps, which is one of the big reasons they suck in snow - AWD or not. They're like rocks.

I think you'd find winter tires would make your car very useful in snow and cold. But you should either find a trusted shop to swap your tires each winter, or get a second set of wheels to keep the winters on.

Or drive something else when it snows. :)