Another ABS/PSM light issue......

Hi there, Got a strange ABS/PSM light issue. Car is a manual MY00 3.4 C4 with 102K (miles). The problem can be almost forced at will - when driving, if I maintain a speed (for example, 35 mph) for about 2 to 3 mins, the lights will come on. A turn off and back on, and the lights go. I've an OBD reader on it and the only thing I could find at the time was error code 4460. What I've done to remedy the problem:- 1. Changed the brake light switch (not calibrated though - didn't think it necessarily the problem due to the lights only coming on whilst the vehicle was in motion) 2. Checked all the rings in the hubs (whilst changing my brake discs) 3. Checked and reseated the ABS sensors. My problem is that I live NOWHERE near a dealership (or Indy) with a Durametric. I'll try the brake switch calibration in the meantime, but what else should I check? Thanks in advance, Dan

How's your battery? When my battery is undercharged, I see this issue fairly frequently (a couple of times a week). When the battery is fully charged, no issue. If you have a maintainer/trickle charger, charge your battery overnight and see if the issue presents again. Do you have stock tail lights, or are you running aftermarket LED lights?

New battery tbh. No LEDs - all stock fittings. Dan

Note the voltage next time you're driving and the lights come on. When you're cruising along, voltage should be a tick under 14. If you're seeing 12.5-13V, might be time to check the alternator wiring and/or voltage regulator. I'd be a dollar (not a pound) that your voltage will be a bit low when you see the lights.

Thanks out of interest, is there a method to see the voltage whilst the car's running? Don't really want to put a multimeter out the window I seem to recall there being a method of using the ac display to show additional info (such as voltage) DAn

I also realise that there's a volts meter in the binnacle But I don't think that's as accurate

Out of interest, why would the voltage drop occur regardless of time in the car (ie having time to heat up etc).... especially if I can get the issue to occur on command (when I drive at a constant speed?) Genuine query - going for a quick drive now anyway DAn

The voltmeter on the dash is sufficient for determining if you're getting the correct output from the alternator.

thanks

Just got back from a drive. Voltage stayed ROCK solid at just below 14v all the way (and the lights came on after about 500m of constant 50mph driving. Am I looking at Durametric? Dan

I'm thinking brake light switch.

I'd thought this initially, so I changed it. However, I didn't know you had to calibrate it? Don't even know how to do it

Out of interest, reading around the net, there seems to a link to a faulty MAF. Although there are NO performance issues. (I recall that a failing/faulty MAF can result in seeing the car hunting for revs at idle.) Am I barking up the wrong tree here? DAn

It CAN be the MAF - but since the MAF is an expensive part, I look for other causes first. Since your voltage is constant, my alternator/voltage regulator theory is out the window - and since your taillights are not aftermarket/LED, that avenue is a non-starter as well. If you know anyone else who has a 996, see if they'll let you switch MAFs for a day. Even if yours is going out, it won't hurt his car any to run with yours for a day - and if the issue remains unresolved, you won't have spent $200 to replace a perfectly good part...

I've also asked a "local" Indy how much for a go on their diagnostic computer..... Will see about a MAF Thanks Any other suggestions? Dan

Quotes source post: 12481607

You shouldn't have to calibrate the brake light switch. It's simply a plug and play solution. Depending on the version of brake light switch you purchased, some of them will allow you to adjust the "plunger" on it. If this is what you are referring to as the calibration, you'll have to find the sweet spot on where it hits the brake pedal engagement. At this point, I would take the car to an indie or dealership to have a Durametric/ PIWIS or equivalent scan although I know you said you are nowhere near one. Perhaps best to order a Durametric scanner. One or two uses will often pay off in itself.

You can also try going MAFless for a bit, since you are able to recreate the issue reliably. Running the car with the MAF unplugged won't harm your 996 in any way, and you'll have a data point if you don't see the issue with the MAF disconnected. As far as setting the brake switch, there are a couple of posts indicating that you need to get that dialed in correctly to eliminate the OBD code you posted:

The later/newer model brake light switches do not allow adjustment of the plunger. It is simply fixed. P.S. - I like your new avatar, 5CHN3LL.

Cool, thanks for that clarification. RE: the avatar, I was lucky to catch Johnny in full meltdown. I'm resisting the urge to go crap in his "oh noes I gots no spare tire" 997 thread... ( https://rennlist.com/forums/997-foru...our-997-a.html )

I would find a Durametric, they are excellent, used mine many times, saved me a lot of money. I had this issue by the way, it was the brake light switch. My symptoms were. 1. ABS/PSM failure light and message to drive directly to workshop 2. After restart this CEL disappeares 3. Light comes on again sporadically 4. The break lights did not work every time I pressed the brake pedal. Back up to a large window or ask a friend to stand behind the car whilst you brake. I found it quite fiddly replacing the switch. Also while searching for a solution to this problem on-line, there were this talk about it being the MAF. And the explanation was; that the MAF produces spikes in current when failing, which results in a false positive error message. Easy to check if you can lend a MAF from a friend, same MAF for 996 and 997 Carreras. If it is the MAF, buy a Bosch MAF not a Porsche branded one, half the price and the exact same one.

I think I stumped the mechanic in Colorado Springs. The dealer sure didn't help any and still charged me the minimum fee. symptom: ABS and PSM lights come on after driving for 3-5 minutes on 2004TT. No difference in driving or engine. The difference for me is I do have an ABS issue. If I approach an intersection and ease-up at the last second rather than holding the brake to full stop, I can get some ABS pulsating. I don't drive in the rain but the streets here are pretty nasty beat up but that doesn't seem to be a common thread. ABS sensor replaced and mechanic tried a new brake switch. The pulsating happens less now and it doesn't force the lights on but it still pulsates on what appears to be solid ground. I bought a new MAF sensor even though it wasn't hunting RPM's at idle but he said the lights come on even quicker with that installed. The lights ALWAYS come on after driving for 3-5 minutes. Rather than throwing out the ABS Control Module, the mechanic is searching for wires that might be over-heating after driving. The ABS wires are not pinched and have enough slack. If I understand correctly, the PSM is going to come on if the ABS drops since ABS is required for PSM. Here are the repairs in the last year or so: new alternator and new battery (it was time.) new clutch assist So, am I doomed to replace the ABS control module? I wish there was a way to put one in and see if it works and remove it if not. I can't figure out why Pelican has this part for $1619 G99635595551 and this part for what appears to be the same thing for $3837 996355955CX. Your help is appreciated (no dumb answers when we're chasing a ghost.) Thanks, --L

Apologies about the delay in replying - stopped receiving notifications for some reason! Not done anything about it yet (life getting in the way), but the car has a service coming up, so will ask them to look at it at the same time. Thanks for your advice so far Wil let you know the outcome Dan

was this resolved?

I had a very similar problem recently where my lights would come on any time I went over 5k rpms. I had no braking or light problems, and nothing performance-wise to give any hints. By coincidence (long story) I had a known good MAF, so I swapped it out and the problem went away. I have a Durametric and it never gave me any codes to work with (lights went off at restart, just like yours). If you have the option, I like Schnell's suggestion, because you will drop around two bills for a new one. R