jasper

Heads up.

2002 996

I just got the car back on the road after a major brake job which included a new vacuum assist servo.

A few hours later I got an error on the dash: ABS fault PSM fault drive to workshop.

Sounds serious...or so I thought.

I was all prepared to start pulling and checking and cleaning my ABS sensors when I found this thread over at Pelican:

http://forums.pelicanparts.com/porsc...lem-cured.html

In that case the fault originated with a flaky brake light switch behind the brake pedal. In my case it was simply a burned out brake light. Either way - when your computer doesn't see a brake light signal it throws an ABS code - which throws the PSM code.

I replaced both brake light bulbs (first time ever by the way) and the problem went away.

Cheap and cheerful.

silotwo

I had something similar just last week. Car had the rear bumper repaired and when I picked it up the same ABS/PSM drive to workshop message was lit up like a Christmas tree. There is a history with my local dealer of all repairs requiring multiple return visits - so I even called and asked the service manager to thoroughly check the car out BEFORE I picked it up. Guess that didn't happen. Anyway, I left the car and according to the dealer it was a fluke, they reset the codes and so far they have not returned.

When they first told me that they didn't do anything that would cause it, I did mention that yes, they had the taillights out. And no, I was done believing that malfunctions that happen during repairs they perform can no longer be written off to "coincidence" of "bad timing".

I also thought I had a serious problem on my hands; luckily it turned out to be a non-issue and I am back to enjoying the ride.

ogun228

Most likely brake light switch.

jasper

Well, I'd argue that burning out a brake light is more likely to occur than a brake slight switch failing, but yes as I stated in my original post ABS PSM codes caused by a faulty brake light switch has been well documented.

The point though is that in my case a burned out brake light bulb also caused the code.

jasper

Whoa - hold the phone. Seems that I jumped the gun. After a day of no drama the ABS and PSM failure codes are throwing again.

I'm on to step 2 which is to check the brake switch. Hopefully that's it but I have my doubts since the errors come up during straight ahead driving rather than while I am operating the brakes.

Nevertheless - it's still the most likely problem at this point. As I explained earlier I seriously disturbed the brake pedal assembly while I was installing my new brake booster.

jordanturbo

MAF code, clean or replace MAF

jasper

A bad MAF will throws a ABS PSM error onto the dash? How does that make any sense?

jordanturbo

Google is your friend, search "ABS PSM MAF" You will see lots of article, it has been discussed many time on rennlist and other places, too lazy to link now.

It happened to me about a year ago, basically I was driving, my ABS and PSM light came on, car ran slightly off, but nothing really to be considered out of the ordinary. I scanned the codes with my scan tool, I did a little research and found that the cause was a fault in the MAF reading incorrectly. I cleaned it and it was fine, I replaced it a couple weeks later when I did a major tune up, and it never gave me problems again until I popped my motor

jordanturbo

LINKY

Its been a while, so I cant exactly remember what the specific codes were, and why they PSM/ABS lights are related to it

Aother LINKY

Another Another LINKY

jasper

Wow - thanks for that Jturbo.

I don't think I'll be bumping this up on my priority list because the car runs fine and I did fiddle with the brake pedal but it absolutely will go on he list if the obvious issues don't pan out.

thanks

jordanturbo

It may be worth looking at sooner rather than later, an incorrectly reading MAF can lead to random misfires, few enough even to trigger a check engine light. If you are dumping unburnt fuel into your exhaust it can screw up your cats. A MAF fix is a lot cheaper than cat replacement.

May be worth bucking up and taking it to someone that has a scanner that can read ABS and PSM fault codes (standard OBD2 readers will not) to confirm. An easy way to confirm if it is your brake switch is see if your brake lights work, if they do, your switch is most likely fine, and replacing it wont get rid of the ABS and PSM light.

jordanturbo

Lastly instead of just throwing parts at it, if you are at all competent in electrical, and have a multimemter, you can measure the voltage off the MAF sensor (it should have set parameters that the sensor sends) if it is operating outside those parameters, the MAF is bad, I used this trick when trouble shooting my blown motor.

It may take a little extra time and money initially, but diagnosing a problem correctly from the start can save a lot of money long term. Throwing parts at a problem until it is fixed can get pretty costly.

jasper

OK - so I removed the brake light switch and exercised it while hooked up to my multi meter. I seemed to function as it should. pins 1&4 would make with the plunger in and pins 1&2 would make with the plunger out.

I extended the plunger completely (that took quite a yank) and reinstalled it while holding the brake pedal down with my hand. Then I slowly released the brake pedal.

Heck I figured let's have a look at that MAF sensor so I removed the airbox (which wasn't strictly necessary), Checked the air filter (dirty-ish but not too bad), and removed the MAF by undoing the two safety -torx screws holding it to the airbox.

The metal probes inside the end didn't look dirty - but I doused them with electrical contact cleaner a few times and blew on them to dry them off.

Then I put it all back together and went for a drive. It didn't throw any codes but I've been at this too long to believe I solved the problem. We'll wait and see what comes up and when something does I reckon I'll read the codes and fix what they tell me to fix rather than throwing parts at it.

It isn't all that bothersome. The car runs fine and the brakes feel great. I don't think I have ABS or PSM while the errors are up - but whatever.

jasper

OOps - just saw your post.

All good advice and this is something I will do if (when) the codes come back.

The warnings clear every time I restart the car and I actually drove home today without any errors coming up. If it is the MAF I wonder if the voltages are sometimes in spec and sometimes out.

My brake lights work fine by the way....very early in this thread I discovered one bad brake light bulb but that was a red herring.

Thanks for the tips JT.

jordanturbo

Those were my symptoms exactly, except my would turn on all the time. Ever time I started the car there would be no lights, then within a minute they turn on. Reason for this is that the computer does not take data from the MAF right at start up (it doesn't use O2 data either), it relies almost solely on Crank Angle and Position sensor. If you actually have a scanner and look at MAF and O2 values on start up, they are always out to lunch which is why the car has a high idle and once the car feels the MAF and O2 data is accurate it will start using its data.

The reason mine would turn on every time was that I had a K&N intake with a filter that was over oiled from the manufacturer, and the oil from the filter contaminated and killed my MAF.