A problem cropped up last night. Car had been running for about 10 minutes and during that period had a minute or so of sustained boost, through 3rd and 4th. Then traffic on this dual carriageway then meant progress backed off to 50-60 in 5th. A few minutes later I was queued at a set of traffic lights, then moved off in 1st and detected a 'rise and fall' of boost. Went to 2nd and there was no boost. I recognised this as limp mode, so pulled in and turned off the ignition to see if a reset would clear it. No such luck though and this 2nd start was accompanied by the CEL light.

So I completed my journey in non-turbo mode then hooked up VAG-COM, with the following result:

17964 - Charge Pressure Control: Negative Deviation

P1556 - 35-10 - - - Intermittent

Readiness: 1 1 0 0 1

I cleared the fault had no effect, the error returned immediately. I've had this one before so have checked the pipework in case something's popped off. Car's been jacked up etc, but I can't spot anything, however. The Ross-Tech wiki does also mention the turbo VNT mechanism as a possible cause, but the turbo is as new, have been overhauled and upgraded by TD. Plus I can't hear any odd noises, nor hear anything such as escaping air that might suggest a boost leak or broken pipe.

Sorry for the long post, but thought I'd include as much info as possible. So, what's left to check?

Cheers,

Steve

Edited 20 December, 200817 yr by Wardy
Updated VAG-COM fault code

Hazarding a guess - either popped off turbo pipe likely right at the turbo mount (which may be noisy) or blown turbo....

Double check all the pipework especially at the air intake of the turbo...

Same happened to me once and it was a pipe loose on the turbo itself IIRC...

Good luck mate

Bas

Oops - no that wasnt it that gave me the same symptoms- it was that the MAP sensor got disconnected.(Water injection bungling)

Better check that too, especially if you're running a FMIC and the symptoms had a pop at the start...

Sure someone will come along and coldly point out exactly where the fault is based on the scan but till then...

Cheers for that Bas. There was no 'pop' as I've had before with pipe related issues, just this slight surge then nothing....

And there doesn't appear to be any odd turbo-related noises. I might have to have a closer inspection of the pipework fitted directly to the turbo.

Cheers,

Steve

Thinking on, something that's probably worth mentioning is that when I cleared the code in auto-scan within VCDS, when it scanned again as part of the clearance procedure, the fault code was right back there again. Now the engine obviously hadn't been run in between, so does this point me towards a sensor fault/failure of some kind?

Steve

black box on the O/S wing top

Vacuum box you think then Ric? Hmmm, changed that for a new one quite recently

You reckon I should pop the old one back on and see what happens?

Steve

got to be worth a try Steve

also check all the vac pipes to/from the unit

I had a similar issue with a 115 PD engine'd Golf and it turned out to be the air flow meter. Know anyone with a VAG car locally that you can have a loan of thier AFM to try??

Well I'm now probably more confused

Popped the old vac box back on this lunchtime. Then cleared the 17964 code and it stayed off when I re-scanned. On test drive however there appears to be some boost, but not nearly enough. Engine check light has stayed off however :confused: So the issue appears slightly better, but by no means fixed.

On returning from a 6 mile or so test drive, I re-scanned and the code had re-appeared again. But still no re-appearance of the engine light.

Think I've run out of things I can try personally; will try Awesome next I think, to see what can be discovered. Fingers crossed!

Cheers,

Steve.

What a coincidence, I've had the same problem this morning with mine! Dealer has ordered a new vacuum box to be fitted on Saturday, am hoping that will cure it.

Here's my vag-com reading, bear in mind I've removed the EGR too:

Address 01:Engine

5 Faults Found:

19557 – Motor for Intake Manifold Flap (V157): Open or Short to Ground

P3101 – 35 -10- - - Intermittent

19558 – Motor for Intake Manifold Flap (V157): No Signal

P3102 – 35-00 - -

17564 – Manifold Pressure Sensor (G71): Open/Short to Ground

P1156 – 35-10- - -Intermittent

17964 - Charge Pressure Control: Negative Deviation

P1556 – 35-00 - -

18000 – Altitude Sensor / Boost Pressure Sensor: Implausible Correlation

P1592 – 35-00 - -

Readiness: 1 3 0 1 0

How much was the new box, out of interest?

I only have that one error, but for mine any EGR issues have been mapped out by Jabba for the Allard bypass pipe.

Steve

Have you checked the Map Sensor Steve?

Hi

Mark says check the VNT it working.When engine is cold , you can check it is getting full movement 13 to 15mm`s

Sorry

Sarah

How much was the new box, out of interest?

I only have that one error, but for mine any EGR issues have been mapped out by Jabba for the Allard bypass pipe.

Steve

I think the box is going to be around £120 inc vat, and under an hour's labour which is £70 at the most.

Have you checked the Map Sensor Steve?

Not yet Stu. What would you check? Just that the physical connecion is present, or anything else?

Cheers,

Steve,.

Well I think your earlier deduction of a fault without starting the car is a good point, so first making sure it is plugged in and then if necessary changing it.

Have you got any other codes?

You can test the N75 as follows -

Actuator diagnosis

With the actuator diagnosis the following parts are activated in the sequence indicated:

1 - Exhaust gas recirculation solenoid valve -N18-

2 - AC compressor engagement

3 - Solenoid valve for charge pressure control -N75-

4 - Change-over valve for intake manifold flap -N239-

5 - Glow period warning lamp -K29-

6 - Radiator fan control

7 - Glow plug relay -J52-

8 - Low heat output relay -J359-

9 - High heat output relay -J360-

10 - Fault lamp

♦ Actuation of the individual control elements is limited to 30 seconds.

♦ If the actuator diagnosis must be repeated without the engine being started in the meantime, switch off ignition for about 20 seconds.

♦ Fuses according to current flow diagram O.K.

Procedure

– Connect vehicle system tester. Start engine and select address word 01 „Engine electronics“

Enter function 03 Output Tests

You should try to hear the N75 click Steve.

Cheers Stu - I'll work through the above. There's no other codes at all.

Steve

Sorry to hear of your problem, Steve. Hope you get it sorted soon.

Too much tinkering, perhaps? Oops, I felt that.

Good luck.

Yes indeed; it's all the turbo's fault!

New vac box (or solenoid valve block to give the proper term) was procured for the VW dealer and fitted this lunchtime. Still the same symptoms, so that's it out of the equation.

DV, MAP sensor or VNT mech left then, plus it's still possible I've missed a pipe connection issue. So it's booked into Awesome on Tues morning, who have very kindly managed to squeeze it in at short notice.

But if anyone else has any more thoughts in the meantime, feel free to shout

Cheers,

Steve

Does that mean I get my valve block back then?

Yes it does, if you want it

Can't rule out that it wasn't playing some part in the issue, but on the other hand could still be 100%.

Any more ideas for possible resolution, o great one?

Steve

It wont be the map sensor as that is correlated against the atmos sensor on the ECU.. will throw a implausible correlation code if it was.

Maybe a holed pipe between the vacume box and VNT solenoid, or a sticking VNT mech..

What a coincidence, I've had the same problem this morning with mine! Dealer has ordered a new vacuum box to be fitted on Saturday, am hoping that will cure it.

Here's my vag-com reading, bear in mind I've removed the EGR too:

Address 01:Engine

5 Faults Found:

19557 – Motor for Intake Manifold Flap (V157): Open or Short to Ground

P3101 – 35 -10- - - Intermittent

19558 – Motor for Intake Manifold Flap (V157): No Signal

P3102 – 35-00 - -

17564 – Manifold Pressure Sensor (G71): Open/Short to Ground

P1156 – 35-10- - -Intermittent

17964 - Charge Pressure Control: Negative Deviation

P1556 – 35-00 - -

18000 – Altitude Sensor / Boost Pressure Sensor: Implausible Correlation

P1592 – 35-00 - -

Readiness: 1 3 0 1 0

The 18000 code usually indicates a dodgy MAP sensor... (the car will stay in limp mode while its there)

The other ones worry me, as iirc all those sensors are on the same section of the wiring loom :eek:

The 18000 code usually indicates a dodgy MAP sensor... (the car will stay in limp mode while its there)

The other ones worry me, as iirc all those sensors are on the same section of the wiring loom :eek:

They worry me too!

Turns out that it wasn't the vacuum box, but the Thrust Sensor in the intercooler. Part was £37.95 + vat and an hours labour. Car drives well now

Part number is S038906051C