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Discussion Starter #1
Bought 2002 PT Cruiser for my son this past summer (Aug 2012). No problems with transmission until winter hit here in Texas last month (Dec 2012). The transmission goes into limp mode when the outside temperature dips down to the 30's. When the temperature is warmer (50's and up) it runs fine with no problems. Sometimes when running errands on a cold day it may come out of limp mode on a random basis. Also, when this happens the check engine light comes on with the P0700 code. Any advice on what to look at first (based on the fact that this outside temperature related) would be very helpful and appreciated.
 

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Welcome to Allpar. P0700 is just a PCM (powertrain control module) code telling you that a code is stored in the TCM (transaxle control module). It has no real diagnostic value. You need the fault code stored in the TCM for diagnosis.
You may get the needed code in the instrument cluster self test (see video) if it appears in the odometer display, otherwise you will have to find someone with a more specialized scan tool that can read Chrysler TCMs.

http://youtu.be/2mtmyl5VDFY
 

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Welcome to the forum. Another item to think about, which may clear the problem of limp mode is a changing of the transmission fluid. As fluids get colder they tend to thicken, and when they get thicken then contaminants tend to remain in the fluid more. The contaminants, as the fluid warms up or is warmer, tend not to stay in the fluid as much, thus when cold they could be causing problems. Key point is, when it is warmer the transmission doesn't go into limp mode. I would be real surprised if ice and moisture outside the transaxle is causing a temporary short of sorts that disappears when it gets warmer.
 

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Low fluid levels will get even lower in cold temperatures and rise as it warms.
Checking the level on the dipstick is always a good and easy first step in diagnosis. Fluid condition can determine whether it should be changed. Fluid additives do wear out. ATF+4 is a synthetic with excellent cold operation properties. Use ATF+4 only.
Going into limp-in will generate a TCM fault code that also has diagnostic value.
 

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cold temperatures can affect many things,some electronic components can fail in lower temperatures
as well as a weak battery causing computer faults.
 

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I had the off-roader problem as he noted.

My bad batery wires made the PCM throw deceptively faulty code(s). My local dealer tried to soak me with the code repairs when in reality it was the $45 in battery cables that were the real problem.

As a result I have zero faith in the dealer.
And I didn't let him do the unneeded repairs.
 

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Discussion Starter #7
Thanks to everybody for the input so far - here is an update on my situation.

Did a transmission filter/fluid change and it did not make any difference. I used ATF+4. Ran it up to Autozone and they were able to get some additional codes (P0605 & P0731). I replaced both of the transmission speed sensors.

Temperature has been warmer the past two weeks so no symptoms until this morning when the temp dipped back down to the 30's. It started out in limp mode (w/ check engine light on). I turned it off after a mile and restarted it - it then drove normally (check engine light on) to work. Drove fine to the house after work - made one stop on the way and the check engine light went off on the last leg of the trip.

Right now I'm leaning towards replacing the TCM. I will try to have a transmission shop take a look at it but I'm not sure if they will find anything on their courtesy inspection since the check engine light is off and the temp is forecast to be warmer for the next week or so.

As always, any advice is greatly appreciated.
 

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Even with the 'ck eng' light off, a fault code is still stored in either module (just don't disconnect the battery, it will wipe out the memory). It just means that the fault isn't active at this time.
P0605 (internal ROM-write fault) may mean automatically replacing the computer (PCM or TCM) module. I always like to see the code happen a 2nd time to be sure. There is no fix other than module replacement.
P0731 (gear ratio error in 1st) may mean that clutch slippage occured. Could be low fluid or loose valve body bolts or worse.
Neither fault code was for the speed sensors and the old ones are probably still good.
 

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Discussion Starter #9
For what it is worth, it did take me a few drive cycles to get the transmission fluid up to the proper level after I did the fluid/filter change. I'll cross my finger that was the source of the P0731 code. Going to try to swing by a transmission shop to get the codes read again today - if the P0605 & P0700 come back up is there anything else I should try before committing to a TCM replacement?
 

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disconnect battery,pull left front wheel and fender liner.
disconnect and remove pcm.
look for moisture in the connector and inspect the condition of the box.
my 01 pt trans controller was corroded so bad it had holes in it.
moisture will wreak havoc on any electronic device.
during my investigation,i found moisture in almost all
connectors.
 

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Discussion Starter #11
Another issue which may or may not be related is that at idle the needle on the tachometer is just above zero rpm and nowhere near the "1" (or 1000 rpm) mark which I would typically expect the needle to be just under at idle based on the normal sound & performance at idle. When I press on and let off the gas the tach needle goes up and down as it should in relation to the motor speed.

My basic school of thought is that this would not be related because the tach would be dependent on a signal from the crankshaft position sensor. Since there is no crankshaft position sensor errors and the motor runs fine with no observable issues with performance (holding idle, accelerating, etc) I'm assuming the problem is with the tach in the instrument cluster.

If I am off on my logic - please set me straight.
 

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Discussion Starter #12
Also, back to the original P0605 issue, I will give removing, inspecting, cleaning connections, and reinstalling the TCM a try this weekend since cold weather is forecast again next week.

If the P0605 fault happens again after that, is there anything else to try before I buy and install a pre-programmed TCM? Also, when a TCM is pre-programmed with the mileage and VIN is the pinion factor set (or reset) in that process?
 
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