PSM and ABS off (again)

[Gimme Shelter]

996 TT: did a 100-mile round-trip today. On the way there, after about 10 miles, and the first chance to open the car up (on a dual carriageway), on came the ABS and PSM warnings, which stayed on all the way there. Return trip, started the car, no warning lights. After about ten miles, dual carriageway, foot down, on came the ABS, PSM and Engine Check warnings. *Exactly* the same symptoms as in January, when an air mass sensor (MAF?) was diagnosed, and a new one fitted, which seemed to sort the problem. Now ([]) that was only 250 miles ago. Do these cars eat air sensors? Or is there another diagnosis, or even a deeper root cause, which is destroying air sensors? (Being a Bank Holiday, I haven't had the car diagnosed this time, of course. I'm just getting a bit fed up.)

Any help appreciated.

 

[Gordon Attar]

My understanding was that this problem was a known sensor issue usually a power steering related sensor, I dont have the info to hand will try and get later.

Not sure why a diagnosis MAF sensor would have any relationship to PSM or ABS

 

[minny]

The ECU uses information from various sensors to keep the engine running within tight parameters and when PSM detects a skid it first tries to control it by braking a wheel to correct the skid. If that is not enough it will also cut power to the engine and this is where a faulty air mass meter can cause the PSM and ABS light to come on. Faulty abs wheel sensors, mismatched tyres with different rolling circumferences, low voltage from a failing battery or alternator, faulty brake light switch can also cause these fault lights. Best to get a diagnostic check with a Durametric/PST/PIWIS which should point to the problem quickly.

 

[Richard_Hamilton]

As Min says, a diagnostic check is the first point of call.

The reason why a MAF sensor problem can cause the ABS/PSM light to come on is that the DME and PSM/ABS modules communicate with each other. If the DME sends an implausible signal (caused by a dodgy MAF) to the PSM/ABS controllers, it will throw the ABS & PSM lights. On RoW cars, a dodgy MAF will not switch on the Check Engine light, but will store a fault code in the memory.

Again, as Min says, an ABS sensor or brake light switch are the two other common culprits.

 

[Buddy]

I had the PSM Fail warning come up once and found that all of the items controlled from the column switches were inactive, indicators, lights, trip computer, WHY Diagnosis showed that a fault in the Chrono system had caused the faults and so a replacement Chrono was installed. Covered by warranty but I was told in excess of £500.

I thought that as this was an optional item and the majority of the rest were std fitment it seemed strange but then it depends where the power supplies are through obviously not separated.

 

[Gimme Shelter]

Thanks, guys. I'll get a diagnosis from my indy (Northway) and let you know.

 

[AndrewEllinas]

I had this problem and a change of brake light switch sorted it - fingers crossed!

 

[a d ousley]

HI HAD SAME FAULT ON MY 996 TURBO ABS PSM WARNING ON DASH DIAGNOSTIC CODE SAID MAF SENSOR BUT PROBLEM WAS JUST INTERCOOLER RUBBER HOSE HAD BLOWN OFF ITS JUST A PUSH FIT AND THE CLIPS WEAR OUT IT HAPPENS IF OVER BOOST ON TURBO WHICH USUALLY HAPPENS WHEN YOU PUT YOU FOOT DOWN MINE WAS THE LOWER CONNECTION BEHIND REAR WHEEL LINER BUT ALSO TWO TOP CONNECTIONS IN ENGINE BAY JUST ABOUT VISIBLE I HAD MY DIAGNOSED AND REPAIRED AT PORSCHE SPECIALIST AUTOFARM THEY SAID COMMON ON TURBO COST £175 TO REPAIR BUT NOW I NO WHAT IT IS IF IT HAPPENS AGAIN TAKES ABOUT TEN MINS TO REPAIR HOPE THIS HELPS CHEERS ADAM

 

[Gordon Attar]

Further to earlier note, it was Steering angle sensor, looks like a large polo that went around steering column part number 996.652.211.01

 

[Gimme Shelter]

Thanks, guys, for all the info (we ought to compile a list of these minor faults that cause the ABS etc lights to come on).

I took the car to Northway yesterday. They found it was a little rubber hose that had become detached from a turbo boost equalising valve (or some such) - it's a small grey rectangular unit, smaller than a matchbox, that sits just behind (rearwards of) the throttle body, just to the right of the inlet ducting above the centre of the engine. To be fair, I should have noticed that the turbo boost gauge wasn't reading sensible figures. With the hose reconnected, the boost gauge gives readings you'd expect, moving from 0.0 bar at a gentle cruise smoothly up to about 0.6 bar at full welly. With the hose disconnected it was apparently sticking at 0.0 bar then jumping suddenly to high figures.

Northway spent nearly an hour in total, diagnosing the problem, test driving the car, and showing me the problem and the remedy. They refused to charge for any of this - top people.

 

[Gordon Attar]

David
I didn't realize that was you sat in reception yesterday I was mainly talking to Ray, I was the one stood on the yard talking to Lee just before you went for your road test .

 

[Gimme Shelter]

Gordon
Well, my Goodness, it's a small world!