996TT shows PSM and ABS failure under hard acceleration

[Krosus]

2004 996TT

Every now and again I get PSM and ABS failure warnings under hard acceleration which can be cleared by just switching off then on again. Usually occurs around 5000 RPM. Other than the dashboard warnings there are no other symptoms and the ABS does appear to be working (can't tell about the PSM).

Possibly related but occurring more randomly, my PCM resets itself for no apparent reason.

Anyone any ideas on this. I suspect a loose connection somewhere, but where?

[fioran0]

somewhere in the dark recesses of my mind i remember folks saying this was a MAF sensor failing.
not sure what the PCM is though. two separate issues possibly.

[Luke.]

I had the same thing on my 986s. It was a faulty brake sensor. Replaced easily enough for not a lot.

[guyvert1]

Had exactly the same on my old one, again, was MAF, are you getting any loss of power?

[steve singh]

As above - with the addition it could also be the wheel sensor.

[Krosus]

Thanks for the replies guys.

Since posting I've found a few threads on Rennlist about this problem. The MAF appears to be the number one suspect. I fitted a BMC air filter about 6 months ago and this may be the root cause. It seems that the MAF gets contaminated by oil from the filter and starts acting up.

Since it's a relatively easy job, I'll remove the MAF and check for contamination. Anyone know if the sensor can be cleaned or is a replacement needed?

I'll maybe put the stock air filter back too!

Thanks again guys

[Krosus]

guyvert1 said:

Had exactly the same on my old one, again, was MAF, are you getting any loss of power?

I hadn't thought about it until you asked but I have noticed a momentary dip in power at high revs at times. Definitely suspecting the MAF now.

Who has the best price for a replacement?

[996ttalot]

Krosus said:

guyvert1 said:

Had exactly the same on my old one, again, was MAF, are you getting any loss of power?

I hadn't thought about it until you asked but I have noticed a momentary dip in power at high revs at times. Definitely suspecting the MAF now.

Who has the best price for a replacement?

You really need to log the MAF values using durametrics. This is where it really pays instead of buying something that you might not need. Most MAF issues are associated with lower rev hestitation issues. I am not ruling it out though. Another test you can do is switch the PSM off, and then retest - if it doesn't come on then it could be a wheel sensor. If you had durametrics then you could see what pcodes it trips which would make it easier.

To clean the MAF just get some Electronic Solvent cleaner and you can unscrew the MAF with a T-20 torx bit. It is quite a simple job. "Oiling" filters have been known to cause this issue.

[SaucyBoy]

I've had this twice mate. the first time was the MAF and the second was a brake switch. Get it plugged in by an Idie to be sure.

Jim

[Ian_UK1]

Luke. said:

I had the same thing on my 986s. It was a faulty brake sensor. Replaced easily enough for not a lot.

I had this problem on a 996 (Carrera, not Turbo admittedly) and it too was caused by a faulty brake sensor - in this case the one above the brake pedal that switches on the brake lights when the pedal is pressed. These switches failed for fun in the (early) 996 - I even used to keep a spare in my door pocket!

The reason this switch can activate the warning lights is that (in adition to switching-on the brake lights) it also lets the traction control and ABS know when braking is initiated. If the control units don't get the right signal from the switch, you get the warnings.

Are the warning lights coming on when you are accelerating or as soon as you hit the anchors after accelerating hard? Whilst accelerating is likely MAF, when hitting anchors is likely brake switch.

Edited by Ian_UK1 on Tuesday 25th January 17:27

[Martian O]

Just on a side note, I've used K&N and BMC filters for years with no probs whatsoever with MAF oiling/fouling.

Edited by Martian O on Tuesday 25th January 17:46

[Ian_UK1]

Martian O said:

Just on a side note, I've used K&N and BMC filters for years with no probs whatsoever with MAF oiling/fouling.

This ^^^^

[Pope]

Check the Y pipe connections, especially the small elbow on the right - the solenoid valve to the Y pipe just before the throttle body - an air leak can give this fault as well.

[Krosus]

Sorted now.

I put the Durametric on it and it showed a MAF fault.

Bought a new Bosch MAF on Ebay. I know that is a bit of a gamble but it is a genuine Bosch. Comes in a sealed Bosch box @ £155. It actually has both the Bosch and Porsche part numbers on the body, so that gave me more confidence that it was the correct part. Next cheapest was from Emission Control @ about £165.

Problems have gone away and the performance has greatly improved. I hadn't noticed the slide in performance over time and was amazed by the amount of power I must have lost.

As I type this, the old MAF is in a zip lock sandwich bag with about 200ml of electronic cleaning solvent. A small amount of black gunge has collected in the bottom of the bag and the sheen has returned to the wires, so the old one will be kept as an emergency replacement.

Thanks to everyone for their help and suggestions and if anyone wants further details of the bits or suppliers I've used, get in touch.

[steve singh]

Good news - thanks for coming back to update.

[Mr Freefall]

Krosus said:

As I type this, the old MAF is in a zip lock sandwich bag with about 200ml of electronic cleaning solvent. A small amount of black gunge has collected in the bottom of the bag and the sheen has returned to the wires, so the old one will be kept as an emergency replacement.

Do yourself a favour, put this old one back in and see if it works. If it does, then wrap it up well and keep it in the car along with the tools to change. If it were ever to happen again and you were on a long journey, or away from home, its a simple swap out then.

Gary

[AndrewMontgomery]

Mr Freefall said:

Do yourself a favour, put this old one back in and see if it works. If it does, then wrap it up well and keep it in the car along with the tools to change. If it were ever to happen again and you were on a long journey, or away from home, its a simple swap out then.

Gary

I would be interested to see how the old one performed after being immersed for some time too. I may be trading my car for a 997 turbo but if that falls through I might replace the MAF (or immerse clean like you) as I have had the odd problem you describe.

[dbmies]

I have similar situation in that the ABS and PSM lights come on intermittently with cold start. It does not occur when I brake. The lights come on mostly when I let off the accelerator with a cold engine. Once the lights are on, the engine surges and idles poorly - oscillates around correct idle speed.
Once hot, turning the ignition off and back on clears the ABS and PSM lights and the car runs great. I never experience this problem at full throttle like some others in the thread.
Infrequently the CEL throws a code for the MAF (maybe 3 times in the past 6 months). Visual inspection detects no problem - MAF is shiny clean - and hitting it with contact cleaner did not make a difference.

Should I be confident I have a bad MAF? Anyone have the part number on hand? I replaced once before at ~40k - probably 8 yrs ago. Thanks.

996 with 86k miles

[Callughan]

Every merc I have had has done this, eventually with their version of piwis they programmed the warning off as it was actually working. Only thing that was always at the back of my mind is how wouLd I know when there was a malfunction

Edited by Callughan on Wednesday 13th February 19:33

[Fantomx]

I've just had my 996tt x50 mapped and fitted with a nuvolari sports exhaust (cat delete) inc with the map and on prolonged acceleration in 4th gear I get these psm/abs failure, this didn't occur before, a quick chat with Ken at 9e confirmed a boost leak at the higher levels.. He recommend new boost hose clips !