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sprinkles08, ASE Certified Technician
Category: Car
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Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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dodge ram 1500 5.7: Have a duel fuel / LPG 2004 dodge Ram 1500

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Have a duel fuel / LPG 2004 dodge Ram 1500 5.7 changed from gas to LPG it ran a bit rough which was strange, pulled over lightening bolt warning came on. It runs ok now but will not go into overdrive and the tow / haul won't work. displays ? PO129 barometric pressure is low.

Any ideas

Hello and welcome to JustAnswer!


It sounds like the transmission is in limp-in, which would give you only third or third and fourth gears.


The P0129 is pretty surely being set by a bad MAP sensor, which is on the front of the intake. It reports intake vacuum to the powertrain control module, when the key is initially turned on or at wide open throttle the PCM takes a barometric pressure reading from it. P0129 sets when the barometric pressure is out of a possible range, this code set with no other MAP electrical codes pretty much guarantees a bad sensor.


The MAP sensor couldn't cause limp in but may cause driveability symptoms mimicking it. I'd go ahead and replace the MAP sensor first and see how it does.


If it still won't shift then the first thing that will need to be done is read the fault codes from the trans controller. If it's in limp-in then there will be codes stored in the TCM and diagnosing the problem will first require knowing what codes have set.

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