Fault 00575 - Manifold Pressure Sensor

**BadgerBoy** · 01-05-2009,07:17 PM

Hi all, a bit of advice please!

I have late 97 Passat 110Tdi and the car has suddenly (ie 2 days ago) started going into limp mode and throwing back the fault code 575 - the manifold pressure sensor. If I delete the code and drive very gently, the code does not return but as soon as I use any real throttle input, back to limp and the same code. Even though stored in the memory, it seems to come out of limp mode if I turn off the ignition then restart but as limp kicks in as soon as I use any real throttle input, I can't be sure.

I replaced all the vacuum pipes with silicon a few months back and have checked all these and all are fine. I have checked the VNT on the turbo is working - I don't have a vacuum pump but even sucking the pipe generated free movement of between 15/20mm. I have visually checked all related wiring that I can get to and there is no chafing/rubbing through to be seen.

After reading all the forums I could find last night (some rather conflicting advice out there!), I'm coming to the conclusion that the N75 valve is the next most likely candidate but I don't want to just go replacing this - lets just say things are a little too tight to be replacing components here, there and everywhere without a certain level of confidence they will sort the issue.

This car does have the pressure sensor at the back of the engine bay on the 2in hard plastic pipe (from the intercooler I think?) rather than the older version with the pressure sensor in the ECU.

So, the main questions: Does the pressure sensor itself ever present any problems or should I just bite the bullet and replace the N75? Or is there anything else anyone would suggest I try first?

Thanks all, your advice is much appreciated.
BadgerBoy

**martin1810** · 01-05-2009,07:57 PM

Looks like it's either the MAP sensor or the turbo sticking. You must have strong lungs to move the actuator by sucking.

**cazyp** · 02-05-2009,07:02 AM

I can move the actuator by sucking. Just because this moves doesn't mean the vanes are opening up - they are kind of on springs (hard to explain) and open depending on boost/load etc can jam due to coke build up but the actuator rod will still move. A good blast(when limp home's not kicking in!)/regular oil change will help keep them working. Otherwise Invotec turbo cleaner is always worth a try.

In my experiance the MAP sensor is the most likely candidate due to the oily/sooty air that flys past it - 2 screws on the hard pipe at the back near the bulkhead with an electic plug. Esp with the map fault code showing. Also worth checking the actuator (black plastic arm thing) on the egr has not split the diaphragm. It should close/open (plastic rod will pump in/out) as soon as the engine is turned off.

Personally i'd replace the map with a genuine vag part before the n75.

HTH.

ChillOut · 02-05-2009,08:16 AM

If you live near Poole, you buy an N75 and I have bought a MAP and we can see which, if either, it is on both cars.

But you don't live nr Poole do you !!

**ini** · 02-05-2009,09:32 AM

It is possible but unlikely to be the N75 valve.

If you have no vacuum leaks, a worn or dodgy air mass meter, or sticking VNT is more probable.

The variable vane mechanism should be very free, and by hand it is almost impossible to detect the catching/sticking that causes limp mode.

Are yousure it is not the intake temp sensor on the top boost pipe on a 97?

**BadgerBoy** · 02-05-2009,10:21 AM

Went to TPS but they didn't have a MAP in stock but car seemed a little better, fault code did not come back on the run there. On the run home, opened it up a bit more and still the fault did not return. It did seem a little down on power below 3,000rpm but once past 3,000, pretty much back to normal. And still no fault code.

Gave the Air Mass Meter a clean with electrical contact cleaner and just used the car again - and the sodding fault is back; felt it go into limp mode at about 2,800rpm. I ran the car a few miles, let it warm up properly, cleared the code then tried again and the fault is back again. I hate intermittent faults! I just don't think the AMM is the problem though.

Cazyp - Thanks for your comments - I'll try and check on your EGR actuator/diaphragm suggestion.

ChillOut - You're right, nowhere near Poole! But thanks anyway.

ini - Mine is Nov '97 and would have been one of the first AFNs with the MAP on the top pipe rather than in the ECU. From what I can tell anyway as I'm not sure where the intake temp sensor would be! I did have the top off the ECU to be sure and there were definitely no vacuum pipes running in there.

I've been hoping it's not the variable vanes sticking but I'm starting to wonder with the fact the fault went away for a little while - I wondered if maybe they had freed off temporarily but then letting the car cool allowed them to stick again. I really hope not though as I'm not sure I'm up to stripping and cleaning a turbo myself.

I shall try the electrical contact cleaner on the MAP as well but may then leave it until Wed when TPS will have a MAP in.

Cheers,
BadgerBoy

**cazyp** · 02-05-2009,03:33 PM

Unusual for TPS not to have a MAP in stock!
When my MAP failed some days/nights it didn't 'limp' much at all - it had good days and bad days!

EGR rod is easy to see - just get someone to turn off the engine while your watch it.

**BadgerBoy** · 18-05-2009,08:23 PM

Hi all,

Well, still not sorted. I had the turbo off at the weekend - I was going to strip it completely and clean it but, after taking the bolts out, it didn't want to come apart easily so I decided against as I was worried I might struggle to get it back together. However, the variable vane mechanism seemed to be moving very freely. I did detect it catching ever so slightly at the end of its travel (the rest position when no vacuum present) but the exhaust intake and outlet had only a fine layer of carbon and working the mechanism constantly for a good 5 mins got rid of the slight catching completely and I could hear the vanes moving freely if I moved the lever quickly.

Also gave the car an oil change and new air filter, checked the condition of all the vacuum and boost pipes I could see and confirmed oil feed pipe clear but the problem is still present, still throwing back fault code 00575 against the MAP. I only have a cheap code reader and was wondering would VAGcom give any more information against the code, ie. if it is over or under boosting etc?

It was mentioned in an earlier reply that the EGR valve may cause problems as well as the N75 (though unlikely) but would these not throw back fault codes specific to those items?

I'm also puzzled as to why the fault only shows up in higher gears - it feels a little down on power below 3,000rpm and then picks up a bit but only in 1st, 2nd and 3rd (though occasionally goes into limp in 3rd at around 3,100rpm) but seems to go into limp in 4th and 5th, sometimes as low as 2,300rpm.

I can't afford to keep replacing parts on the off chance it might sort it but starting to think I might have to give in and take it to a professional but if anyone has any further suggestions as to what I might be able to do myself, they'd be appreciated.

Thanks again to everyone who has tried to help so far.

**martin1810** · 18-05-2009,08:39 PM

Vag-com will tell you if it is under or over boosting. Your description sounds like overboost but you really need a code read. Have you changed the MAP sensor. I would have changed that before taking the turbo off.