P1250 Boost Pressure Control

[Richard Hamilton]

2000 996 Turbo Tip, UK spec, completely standard, 63000 miles.

I had a long-ish drive today – about 190 miles, almost all motorway. On the way back I was cruising at about 3000rpm for about 45 minutes. I pulled off the motorway to a roundabout and onto another major road. As I pulled away the car didn't seem to pick up the revs quite as quickly as normal. Looking at the boost gauge, I was only getting 0.4 bar at WOT and high revs. I normally get up to 0.7 bar. I tried several times, but it wouldn't go beyond 0.4. As I got back towards my office I slowed down to give the turbos a chance to cool down, as I normally do. The engine was running as smooth as silk.

On the way home this evening (a couple of hours after the run) I didn't get much of an opportunity to reach high revs at WOT, but I was able to reach 0.6 bar on a couple of occasions. When I got home I did a diagnostic check and it showed P1250 – Boost Pressure Control. (See attached report). It shows a single instance of a boost pressure of 1.68 bar! The diagnostic sheet says to check the adjustment of the bypass flaps, or change the turbocharger.

So, two questions:

1) Would the P1250 fault have caused the DME to go into a restricted boost program, and if so would it have reset when I switched off? No doubt I am going to have to get underneath to check the flaps, but has anyone had any experience of this issue?

2) I'm not sure if this is related, but it sounds like the SSSHHHUUUSSSHHH noise at high boost has been getting a little louder than it used to be. Where does this noise actually come from? The diverter valves, the by-pass flaps, or somewhere else?

RJH_Error_P1250_140509.pdf

[wross996TT]

Could be the wastegates or bad DVs (yes that is likely the sound you hear). Check to see the WGs are not broken and perhaps replace the DVs. Likely your car went into limp. A reset (battery disconnect) should work unless the faults are still there. GL

[Chuck Jones]

Bill: doesnt that sound more like wastegates than DV's?

If you need another set of DV's....I have an almost new set along with the F hose that I took off my car and replaced with EVOMs that you can have if you need diverter valves....but they are the original OEM plastic ones in good condition and the price is right...but you do pay for the shipping.

[wross996TT]

hey chuck...well it is strange..you would think that blown DVs would do anything but create an overboost situation...but it has happened. I thought first wastegates, but it is hard to do diagnostics via the internet (the sound symptom)....we're just guessing I suppose.

[Richard Hamilton]

Thank you both for the helpful comments. I think the first thing I need to do is get underneath and check the wastegate linkage and actuator. I found a post here http://www.renntech.org/forums/index.php?s...ost&p=43150 where the same fault seems to have been fixed by freeing up the wastegate flaps. (I can't imagine what sort of lube he used that would last more than 5 seconds though). The diagnostic sheet for P1250 says to check the bypass flap settings, so that's the logical place to start. Unfortunately I can't get on to it until next week, but I will report back.

The car is driving fine with normal boost at the moment, so I guess it goes into the restricted-boost program when the error occurs, and resets when the engine is restarted. It's a UK car, so that's probably why I didn't get a CEL, whereas you might on a US car.

Thanks for the kind offer Chuck. I might take you up on it if it isn't the wastegate flaps.

Does anyone have any links, articles or documents with an explanation of the turbocharging system specific to the 996TT? I know a bit about the basics, but it would be nice to read up on how the whole system works. I have the workshop manuals, etc, but they aren't very good in this respect.

[Richard Hamilton]

Well, it seems to have been a simple fix. A clip had come off, and one of the pressure hoses was loose on the intake manifold distributor. Popped it back on, and it all seems OK now (fingers crossed!)