1.6TDI P0299 Boost Pressure Regulation

[dave_ph]

Hi all,

Apologies for bringing this one up again, from searching I’ve seen its been covered many times in many forums, however some are either covered very basically, or in for too much technical depth for me yet!

I just picked up a Mk6 Golf 1.6tdi Match a couple weeks ago. It’s just ticked over 100k miles, been well maintained though. On my way to work last Thursday, as I pulled onto the motorway, I got the flashing coil light and limp mode. Restarted car, was fine for the rest of the day.

Couple days later, coil light comes on straight away, restart car, alright for a few miles, then came on again in limp mode etc. Ever since, even when the light is on, there is no boost pressure at all.

I’ve scanned on VCDS and had the following 2 errors:

2 Faults Found:
7286 - Turbocharger Boost Control Position Sensor Circuit
P2563 00 [175] - Implausible Signal
MIL ON - Confirmed - Tested Since Memory Clear
Freeze Frame:
Fault Status: 00000001
Fault Priority: 2
Fault Frequency: 1
Mileage: 161670 km
Date: 2021.10.31
Time: 07:25:20


Engine RPM: 908.50 /min
Normed load value: 32.9 %
Vehicle speed: 2 km/h
Coolant temperature: 16 °C
Intake air temperature: 14 °C
Ambient air pressure: 980 mbar
Voltage terminal 30: 14.344 V
Unlearning counter according OBD: 40
Charge air pressure actuator: acknowledgment-ANG_BPA[0]: 17.737 %
Charge Pressure Actuator: activation-ANG_SP_BPA[0]: 85.001 %
High press turbocharger actuator: activation-CTL_LIM_BPA[0]: 84.998 %
High press turbocharger actuator: actual uncond volt value-V_BPA[0]: 0.986 V
Turbocharger boost control: offset open-V_BPA_BOL[0]: 0.498 V
Turbocharger boost control: offset closed-V_BPA_TOL[0]: 3.389 V
High press turbocharger actuator: status-LF_STATE_BPA_DISP[0]: 76


7384 - Boost Pressure Regulation
P0299 00 [237] - Control Range Not Reached
MIL ON - Confirmed - Tested Since Memory Clear
Freeze Frame:
Fault Status: 00000001
Fault Priority: 2
Fault Frequency: 2
Mileage: 161679 km
Date: 2021.10.31
Time: 06:35:14


Engine RPM: 2543.50 /min
Normed load value: 40.0 %
Vehicle speed: 69 km/h
Coolant temperature: 63 °C
Intake air temperature: 15 °C
Ambient air pressure: 970 mbar
Voltage terminal 30: 14.456 V
Unlearning counter according OBD: 40
Charge air pressure: specified value-MAP_SP_MMV: 2401.79 hPa
Charge air pressure: actual value-MAP_MMV: 1251.06 hPa
Air mass: actual value (mg/stroke)-MAF_MES: 576.54 mg/stroke
EGR Solen.val.: actual value-ANG_EGRV[0]: 0.000 %
Throttle valve adapter: actual value-ANG_THR[0]: 96.118 %
Charge air pressure actuator: acknowledgment-ANG_BPA[0]: 19.922 %
Engine torque-TQI_SP: 180.00 Nm


Readiness: 1 2 0 0 0

I have little knowledge of the ins and out working of turbos and actuators, however can locate the N75 valve and work out which hose goes where. I’ve visually inspected all hoses for leaks without joy. I read that you can by-pass the N75 to see if boost comes back so tried that earlier (connected the vac hose from the actuator into the “out” hose going to I’m guessing the vac pump, not the hose going to the air box!) and still had no boost pressure.

Does this rule out the N75 being an issue?

If it does, are there DIY ways to test the actuator function or pressure test the vacuum hoses? I’m pretty practical so willing to try stuff. The whole idea of getting this car was to save some dollar, so anything I can before sending to a garage is time well spent.

Thanks in advance!

Dave

[Crasher]

Put a vacuum hose on the actuator and suck on it, if you can draw air it needs replacing.

[dave_ph]

Thanks for your reply :-)

I just tried when I got home. I could draw a bit of air however it built a vacuum up after a little bit then when releasing the pressure you could hear a mechanical release. Is it normal to be able to draw a little bit of air or should it be a case of not being able to draw any? Does that mean the actuator is screwed?

Cheers
Dave

[Crasher]

If the actuator diaphragm is split, you cannot hold a vacuum so the actuator would appear to be OK. Under-boost is nearly always a vacuum control system leak but as they age we are now seeing the position back feed turbo’s throw underboost codes when in the past it would be overboost and this is due to the age old problem of carbon buildup.

[dave_ph]

Thanks for the info!

Would carbon build up result in a gradual increase in the issue (ie going into limp mode steadily more often) or would it just start to cause issues and that’s it?

My problem set in really quickly, was fine then hit limp mode once, was ok for about 20miles then no boost and limp modes constantly

[Crasher]

It tends to be all of a sudden, these electronically monitored turbo's seem to have taken longer to play up in this way than the pervious generation but the common diaphragm failure has added an extra complication to the diagnostic process as they have to be extremely carefully set up. It is quite common for other garages to fit these and then ask us to set them up.

[dave_ph]

I've done a little more testing this eve. I sucked the actuator hose and could see the actuator rod moving up and down, so I'm happy the actuator is working fine. I read that disconnecting the actuator vacuum hose to the N75 value should mean the turbo will boost if its an N75 valve issue. Doing this still gave no boost, so I'm assuming now its an issue with the turbo over anything else?

[Crasher]

The actuator in the no vacuum position is control vanes shut, you need to check at the vacuum source connection on the servo feed pipe, that the system can hold a vacuum; if it does it is likely that the N75 valve is faulty.

[dave_ph]

Hey, sorry for slow reply, been doing some testing!

So I ordered a new N75 Valve (1K0906627B 1J0906627B PRESSURE CONVERTER EGR : Amazon.co.uk: Automotive), not an OEM one, aftermarket but didn't want to spend a fortune on one that would be more difficult to send back than on Amazon!

Put the new N75 valve in, noticed that the hoses weren't as tight on this new valve but gripped. Cleared the error codes with VCDS, fired the engine up, straight away got the flashing glow plugs and same codes as before. Cleared them, took the car for a spin, still no boost. Drove up a gentle hill in 3rd gear and limp mode kicked in. Got home prepared to remove the valve again but noted it was pretty warm which the old one didn't get.

I tried sucking each of the outlets on the original N75 and all outlets would draw air from each other. On the new one, I couldn't suck through the vac outlet, so expect there may have been an issue with the original one possibly? I cable tied the hoses to try and rule out air leaks. They held firmer this time.

Took the car for a test drive, still no boost (but turbo sounded like it was spooling more) until around 3.5k when it definitely started to build boost and pull a bit harder now. Tried to go up the same hill as before, started to pull a bit in higher revs in 3rd gear but hit limp mode then pretty hard.

It seems tightening the hoses gave a little progress, but can't imagine that still being the route cause? Does this give any further clues?

FWIW - the water temp normally sits between 70-90c. If I put the heaters on, it will drop right down. I'm assuming its a dodgy thermostat and not linked to anything else?

Thanks in advance

Dave

[Crasher]

If the gauge reads low then yes, thermostat, are you still getting the same two codes?