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Welcome to Hartech, the UK's leading Independent Porsche engine specialists, located in Bolton, UK

MAF Sensor - Is it Dead?

D

dterry

New member
Joined
12 May 2011
Messages
28
All,

I went out in my car on Friday, it was running fine. On Saturday I decided to give it a wash and needed to move it on the drive. I started it fine, and then as I reversed and then stopped the tickover increased to 2000 rpm for a few seconds and then the ABS and PSM warnings came up on the dashboard. It then started to tickover really lumpy and was hunting a little. I stopped the engine and started it again and immediately the ABS / PSM warnings came on and the tickover was really lumpy and the car was almost stalling. It didn't rev cleanly with small presses of the accelerator and did stall a couple of times. It also smelt "rich".

I have plugged in my Durametric and have a fault code P0102 (Porsche fault code 115 - Hot film MAF sensor) which when cleared immediately re-appears. I also have a code 5525:Incorrect data transfer with DME master control unit on the ABS module which will not clear.

I visibly checked all of the visible cables to the MAF and all seem good.I also cleaned the MAF with IPA solvent as this is something I have done in the past with other cars and it can improve them. However this morning it still has the faults when I put the MAF back in.

I have logged some values with the durametric on tickover and small throttle blips this morning. The values were.....

Mass air flow (HFM) - Sat at 0, never moved
Mass air flow (KG/H) - 32 at tickover, up to 110-115 at I blipped teh throttle to approx 1900-2000 rpm
Hot Film MAF (Volts) - Sat at 0.4 and never moved

Does this signify a dead MAF?
Are there any other things I should check for before throwing £200+ at a new MAF?
Do they really just "die" like this?

I have a multimeter and am capable of using it, is there be anything specific I could check to ensure its not a wiring fault etc? Are there any fuses worth checking?

Cheers
Darren
 
After reading a number of sites it appears that the two codes are probably related and I have decided to buy a new MAF sensor.

I rang a few suppliers and despite them all listing the sensor on their websites I only found one with available stock and they also happened to be one of the cheapest at just under £176 inc VAT and Courier delivery.

http://www.airmassmeterspecialists.co.uk/index.php?cat=911__996_

I'll let you know if it fixes the issue, although I do have an additional finding.....

When starting the car it idles normally for 1-2 seconds and then the ABS/PSM lights come on and the idle speed starts hunting / gets lumpy.
 
It may very well be my mind playing tricks on me, but I swear the service guy at my local PCO told me last week that the car could in fact throw a PSM and ABS error if the MAF dies.

:dont know:
 
Yes, MAF errors ahow as PSM/ABS lights.
 
Out of pure curiosity, do you have any idea as to why that is GT4?

From a systems engineer (me) standpoint, it seems like a unusually absurd design, but there must be some sort of value somewhere that messes with the defautls or acceptable ranges of the ABS system when the MAF goes bad?
 
They ran out of warning lamps, so they started combining them (to allow additional information to be communicated without adding new lamps)

Other options (in similar scenarios of new messages needing to be communicated with limited resources, would be to have a flash sequence, but some Porsche warning lamps can already flash to mean IMMINENT FAILURE etc, so that option was eliminated)
 
Ah see there, see there. That's actually pretty amazingly smart when you think about it.

Guess my experience with software on servers where we have infinate possibilities to throw error codes and tracefiles means I've never had to think about that sort of error reporting.

I'm impressed, not only with the way they solved the (now quite obvious) problem, but also with your knowledge on these matters.

I'm such a happy camper when I can learn something new, thanks :)
 
The DME and ABS/PSM modules communicate via the CAN bus. If the ABS/PSM module receives an implausible signal from the DME (due to a faulty MAF, etc) it throws the ABS/PSM fault lights.

So why doesn't the CEL come on? The reason is that RoW cars do not light the Check Engine light for MAF faults. It only triggers it for some emissions-related faults. On US cars, it will throw a CEL, as they are programmed differently.
 
As I understand it the ABS and PSM need to modulate the throttle when intervening, if the MAF is not working the ECU does not know exactly what the engine is doing and therefore cannot control it, so ABS and PSM are disabled when the engine cannot measure itself effectively.

It is my understanding that the 5525 code is a side effect of a MAF failure. Basically saying that the engine cannot work out torque figures, so therefore cannot control torque via PSM.

I am not sure about the Porsche, but on an Audi TT there is a simple formula that can be applied to the MAF figure (from VAGCom) to give a reasonably accurate BHP figure, so air mass is in some way related to BHP, but I am not sure how closely on the Porsche.
 
Also - I did have a thought that maybe a pipe had come off somewhere and was sucking in air post MAF on my car which would also mean that the MAF would not give a reading.

I proved this was not the case by holding a sheet of paper over the air intake and starting the engine - Air is definately being sucked through the airbox as it tried to pull the sheet of paper into teh airbox opening. So air is passing the MAF. It now looks more and more like the MAF has failed (hopefully), or the wiring between MAF and ECU is damaged / shorted /broken (Hopefully not and what I can see looks OK).
 
dterry said:
As I understand it the ABS and PSM need to modulate the throttle when intervening, if the MAF is not working the ECU does not know exactly what the engine is doing and therefore cannot control it, so ABS and PSM are disabled when the engine cannot measure itself effectively.

It is my understanding that the 5525 code is a side effect of a MAF failure. Basically saying that the engine cannot work out torque figures, so therefore cannot control torque via PSM.
Click to expand...
That's what I said. The signal from the DME is implausible to the ABS/PSM controller.
 
Hi Darren

Sorry to hear about your issues but hope "Terry" has been behaving otherwise.

The car did the same thing shortly after I got it (5 years and 50,000 miles ago) and it was sorted by replacing the MAF.

Cheers

Dave
 
dterry said:
I am not sure about the Porsche, but on an Audi TT there is a simple formula that can be applied to the MAF figure (from VAGCom) to give a reasonably accurate BHP figure, so air mass is in some way related to BHP, but I am not sure how closely on the Porsche.
Click to expand...

Power output is related to air/fuel mass flow on any correctly tuned engine.
 
Dave said:
Hi Darren

Sorry to hear about your issues but hope "Terry" has been behaving otherwise.

The car did the same thing shortly after I got it (5 years and 50,000 miles ago) and it was sorted by replacing the MAF.

Cheers

Dave
Click to expand...

Hi Dave,

Terry (I have to change that name) has been behaving perfectly apart from this issue.

Ther was one other issue that was my own "Special" moment when I flattened the battery and decided to remove it to charge it in the garage overnight rather than leaving a lead trailing across the drive. I stupidly closed the bonnet (or is it a boot) and then remembered it was electrically operated only!

New MAF should be here tomorrow and will hopefully be fitted before (or at) the weekend.

Darren
 
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