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I have an Audi A3 1.9TDI 2000 (engine AHF - not PD - 110ps) - it's done 233,000 miles (new turbo fitted at 147,000 miles)!

I've been getting inermitent loss of power/turbo over the past month, and a fault code is being generated > 17964 - Charge Pressure Control: Negative Deviation
P1556 - 35-00 - -

A month or so prior to that I was also noticing that the turbo kicks in later e.g 2200revs as opposed to around 1500revs.

I have read through the FAQs and started off by replacing all the rubber vac hoses. I also checked all pipes are connected, cleaned the EGR valve. I've also used VCDS-lite to check the MAF output and also the boost pressure (via Measured blocks function) and in both cases the actual values are matching to expected values. I've also checked the turbo actuator rod and this is ok.

When the problems occures you'll a surge, then power loss - and the car is obviosuly in a limp mode (and dtc 17964 is generated). Switching off/on then seems to reset and power returns.

I can't work out what it is, but the one common thing seems to be that it happens within 5-10mins of a cold start (especially first thing in the morning, such as today when it was 5degree Centigrade.

I'm wondering if a temperature sender somewhere is faulty?

Has anyone else had a similar fault or has any ideas???

Thanks-in-advance.
 

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Did you try switching the N75 with the egr solonoid? Or maybe the actuators on it's way out, did you test if it holds vacuum ok? It might be worth checking the map sensor too and maybe giving the plug the once over with some switch cleaner.:)

welcometomyturbodies
 

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How did you check the turbo rod? there's a writeup in the FAQ on how to test it, isolate the problem to the vanes or the actuator using a hand vacuum pump w/gauge. If no gauge you don't really know if it's working or not.
 

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I have this exact same problem. I put a new engine in my TDI PD Bora a few months back and it runs perfectly, bar this one minor issue.

I live on a steep-ish hill and my car only goes into limp-mode if I go up the hill right after the first start of the day, if I go down the hill it doesn't happen.. but like you said, it resets then runs perfectly normal all day long after a simple engine restart and doesn't do it again until the next day or sometimes a few days later.. very odd.

I checked the vacuum hoses and air flow meter, and then thought it was something to do with cold-starting but no evidence & no dtc's stored at all so I am stumped. Realistically, it's not a major problem seeing as it happens quite rarely, just glad to have my car back on the road again after the palava I had before, but it is slightly irritating.. mainly because I don't like not being able to get to the bottom of it :umm

Sorry I have no helpful information or advice of any use to you but thought I'd post to show that you aren't the only one with this mystery.
 
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