I am getting the generic code P0299 Turbo Underboost along with P1250 Vacuum Reservoir Control Circuit Open. The second code comes on first. Sometimes it is Vacuum Reservoir Control Circuit High. The boost comes and goes during the drive. It only seems low on boost right off idle. Higher RPMS are fine. If I clear the codes, it runs fine for a while, throws the code, then it may run normal for a while. It can't be a hole in the inter cooler hose because sometimes I have full boost as normal.
The Shop Manual just says to check for a short. Does anyone have any experience with this?
What is vacuum reservoir and why would that mess with the boost?

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2006 Limited, navi option, dealer tune, Mr Gasket lift pump, Stant 13519 thermostat, Sears P1
Mopar bull bar, roof basket, pet barrier, step rails, off-road fuel cell

Try bypassing the boost pressure solenoid although I would not rule out hoses, even with intermittant boost, unless they have been inspected off the vehicle and after removal of the mesh covering especially if they are 1st gen OEM.

If you want pictures for the bypass shoot me an email.

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Sold to LOST member my 05 Ltd, GDE Stg II turbo + TCM tune, SunCoast TC w. Transgo kit, Steiger window regulators, Samcos, Fumoto valve, 2nd gen filter head with Lub. Spec. bleeder, Hayden clutch & 11 blade fan, inverted spare, P-1 battery, BF Goodrich Long Trail TAs, Etecno1 glow plugs, timing belt at 50K miles/8 yrs

Sounds pretty close to this diagnosis: http://townhall-talk.edmunds.com/direct ... f0f784a/48

Re: Error code P1250 and P0299 [jeepon] by dasboot72
Feb 15, 2010 (8:39 pm)

Replying to: jeepon (Feb 15, 2010 2:37 pm)

Hi, I have been a Chrysler/Dodge/Jeep mechanic for 15 years. I am also the only diesel mechanic at my dealer. The P0299 Boost pressure sensor positive deviation, is a common code in the Liberty diesel. TSB # 25-001-05 Rev. A describes this condition. Essentially your PCM needs to be flashed (Reprogrammed) and the EGR valve replaced. The P1250 Vacuum Reservoir Solonoid open circuit DTC is also a code I've seen in the past. You most likely need a new Vac Res solonoid. It is located on top of the Vac Reservoir which is on the passenger side of the engine compartment. It is a kind of stepped cylinder with 2 vacuum lines going to it and an electrical plug. Hope this helps.


? Mark

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2005 Liberty CRD
2004.5 Cummins 5.9L TD, F1s, NV5600 6-speed in a '93 GMC Suburban

Yep- bad solenoid. Thanks guys! The bypass test worked.

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2006 Limited, navi option, dealer tune, Mr Gasket lift pump, Stant 13519 thermostat, Sears P1
Mopar bull bar, roof basket, pet barrier, step rails, off-road fuel cell