No turbo boost when car is warm (1.4TSI)

**Paul_OH** · 01-09-2013, 05:29 PM

The N75 is the charge pressure control solenoid. I'm not exactly sure what the correlation is between the 2 but when I had the N249 error code, replacing that valve only didn't solve it - only when the N75 was changed also. My N249 Diverter valve was completely screwed though with a torn diaphragm - make sure that the new one fitted is the newest type with a piston instead of diaphragm (VW upgraded it a couple of years ago).

**Mattlock** · 01-09-2013, 05:35 PM

Originally Posted by Paul_OH

The N75 is the charge pressure control solenoid. I'm not exactly sure what the correlation is between the 2 but when I had the N249 error code, replacing that valve only didn't solve it - only when the N75 was changed also. My N249 Diverter valve was completely screwed though with a torn diaphragm - make sure that the new one fitted is the newest type with a piston instead of diaphragm (VW upgraded it a couple of years ago).

Ok. This makes a bit more sense and matches with the reading I've been doing. Forge Motorsport make a valve-based replacement that still hooks in to the stock ECU and it seems to only replace the N249, supposedly eliminating the N249 failures.

My mechanic went out of his way to tell me that the part had been revisions by VW and I had that newer part fitted last week.

**Mattlock** · 04-09-2013, 09:29 AM

So, my mechanic has been through the car again and cannot find any fault codes for the problem but on a test drive with me acknowledged that the problem is still there (can't really miss it).

He ran some specific diagnostics on the N75 and in isolation it appears to be playing up. He wants to understand why there's no fault code for it so he's going to play with it next week whilst I'm overseas before simply replacing the N75.

**Mattlock** · 15-09-2013, 06:22 PM

Originally Posted by Mattlock

He ran some specific diagnostics on the N75 and in isolation it appears to be playing up.

The car is back after a holiday with the mechanic (I was overseas all week anyway). They confirmed it was the N75 that was causing the issues. They replaced it and drove the car cold and hot to make sure it was well and truly fixed.

They said that for some reason the TSI doesn't report in as much detail as the GTI and that apart from voltage nothing else about the N75 is reported up as a fault code. Therefore you only find it's faulty when you run specific diagnostics against the unit.

So it's ended well with the car being returned to full boost after replacement of both N249 and N75. Now for the APR Stage 1 tune...

**The One** · 15-09-2013, 09:04 PM

Originally Posted by Mattlock

The car is back after a holiday with the mechanic (I was overseas all week anyway). They confirmed it was the N75 that was causing the issues. They replaced it and drove the car cold and hot to make sure it was well and truly fixed.

They said that for some reason the TSI doesn't report in as much detail as the GTI and that apart from voltage nothing else about the N75 is reported up as a fault code. Therefore you only find it's faulty when you run specific diagnostics against the unit.

So it's ended well with the car being returned to full boost after replacement of both N249 and N75. Now for the APR Stage 1 tune...

APR stage 1 tune on the 1.4L Twin charged... People are mad.

**Brendan_A** · 16-09-2013, 05:33 AM

Originally Posted by The One

APR stage 1 tune on the 1.4L Twin charged... People are mad.

Why???

**The One** · 19-09-2013, 06:54 PM

Originally Posted by Brendan_A

Why???

CAVD, more like CAV Disaster.

Haha, just trolling

**Paul_OH** · 04-04-2014, 12:22 AM

Lucky the Mk5 version is BLG then and not CAVD

FYI, my N75 failed again, I was able to pick it straight away however again it showed no error code on my Ross-Tech cable nor my mechanic's software. He explained however that the valve suffers a mechanical failure internally and whilst operating properly electrically they fail to carry out their intended function.
Once it was replaced it was all back to normal. As mentioned earlier in this thread I had previously changed to the piston type diverter valve and this was still operating as normal. The mech also confirmed that the N75 has a new revision number from last year onwards (previous part # was a 2006 designation) so VW have obviously identified that there's a problem and upgraded the part.

**Mattlock** · 04-04-2014, 01:40 PM

How long did your last N75 last?

I am assuming that when mine was replaced in September last year, it was done with the revised part. If it fails again, I may switch to the Forge Motorsport unit.