Ive been lurking for a while, this is my first post. I have had an issue with my CRD for a while now, error codes p0234 and p0072 would come up often when I drive 60-70 up a hill, they would typically clear themselves in a day or so. This would sometimes be accompanied by a loss of power, and the trans would not want to shift to a lower gear. On several occasions I used the overdrive switch to force a shift, and the engine would rev up to 3k or so, but only deliver additional power very gradually.
A couple days ago I towed a light trailer to the dump (no hills), and coming home power became very sluggish at low speeds, and two more codes came up, p0700, and p0770. Now it is sitting and waiting for my attention.
I am hoping that addressing the tranny codes will ultimately address the other codes, as those have persisted through a thorough intake cleanout and new EGR
Should I change the indicated transmission sensors, or is it likely more complex than that? Any simple tests to perform? It may very well be over my head...
Thanks!

Others may want to weigh in but my
1. P0234 - BOOST PRESSURE SENSOR NEGATIVE DEVIATION - might be the sensor or might be sticky turbo vanes which can be checked per GDE by "Underneath the vacuum actuator on the turbo is rod extending downward connected to the vane mechanism. If you pull off the vacuum line at the turbo, the arm should drop about 1/2 inch and then raise back up after reconnecting the vacuum line. It is a bit difficult to see the rod, but this is the easiest method to check for proper VGT vane movement."
2. P0072 - AMBIENT AIR TEMPERATURE SENSOR CIRCUIT LOW - unfortunately while the FSM contains some diagnostic information it omits any information about the location of the sensor. I wonder if it's the MAP sensor (see Sir Sam's NOOB guide) which the parts fiche calls an "air temperature/boost pressure sensor" so it may relate to both these codes. A cheap replacement is Bosch 0 281 002 845 or GM PN 55206797
3. P0700 - a generic transmission code that just says a transmission code is stored and you will have to get someone with an appropriate code reader to pull the code. Any decent tranny shop should be able to as the 545RFE is a widely used DCJ tranny.
4. P0770 - 4C SOLENOID CIRCUIT - appears to point toward a transmission solenoid issue.

Don't get a new EGR either clean the one you have, email me if you want how to, or bypass/get a tune to turn it off.

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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

Sound like you might need a new MAP sensor.

Also, its common for this transmission to develop problems with the solenoid pack. The solenoid pack can be replaced by draining the transmission fluid, removing the pan, and removing the valve body.
While you have it apart, you should definitely replace the transmission filters and may want to consider installing the TransGo HD2 shift kit.

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U.S. Army Retired

Thanks,
We replaced the air temp sensor, cleaned out some of the connections, replaced the alternator which had a bad clutch. It seemed fine, but shortly popped back with the p0700 code and p0988 transmission fluid pressure sensor/switch "E" code, and seems to be in"limp mode" with low power. There seems to be some bypasses wiring in harness from previous owner, and I'm wondering if it may be a harness issue. Is there a way to tell if it is a wiring issue vs sensor?

Where are these wiring bypasses?
Are they near the TCM or down at the transmission?

I say try replacing the transmission pressure sensor first to see if that fixes it.

Edit:
It appears that the p0988 code points to the solenoid pack.
Have you checked the fluid level? Maybe it's low?

_________________
U.S. Army Retired

Add some ATF+4, these transmission are most happy with a little overfill....
Have you serviced the transmission? If not, drop the pan and change the oil and both filters and refill with fresh ATF+4 and add a little above the full mark...

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Supporting Vendor and Moderator of LOST
05 Jeep Liberty CRD Limited
Ironman Springs/Bilstein/Shocks
Yeti StgIV Hot Tune
Week's BatteryTray
No FCV/EGR
Samcos/ProVent
SunCoast/Transgo
Carter Intank-pmp
2mic.Sec.Fuel Filter
Flowmaster/NO CAT
V6Airbox/noVH
GM11 Bld.fan/HDClutch
IronrockArms/wwdieselMount
98 Dodge Cummins 24 Valve

Thanks All,
The fluid level is normal, though I will top it over a bit as per WWs' recommendation
The wiring bypass runs from the TCM down to the tranny (can send pics if need be).
For what its worth, if I pull over and shut the motor off, the tranny usually goes back to normal shifting, for a while anyway.
I am thinking I will open the tranny, install a TransGo HD2, replace the solenoid pack, filters, and see where the bypass attaches in the transmission. Sound reasonable? Anything else I should do while I'm there? Any estimate on how long that will take me in my driveway? I have some experience, but it's been a while...
Thanks again, I'm dying to not see a little yellow engine on my dash.

Can anyone tell me how to test the solenoid pack? Either in or out of the tranny, so I can confirm I am addressing the right problem? Also, a heat sensor code came back, after we replaced one by the radiator, is there one in the tranny to replace? I got my backup vehicle registered, hoping to do this work ASAP...

I'm sure there is some sort of special tool set for testing the solenoid pack but I dont know what it is. A good transmission shop might know.

Which temp sensor code?
Engine temp?
Transmission temp?
Intake air temp is the MAP sensor.
And there is a sensor on the lid of the air filter box. Make sure its plugged in.

_________________
U.S. Army Retired