QuestionQUESTION: Roland:
Have a Chrysler 300m which had the speedometer go out. Changed the ouput speed sensor and the speedo did not come back. But the car then threw a P0715 code for the Input Speed Sensor. I changed that and the speedometer started working again. The car will start out okay and use all gears (auto or manual mode) but then for unexplained reason, do a hard downshift going into a stop. After that, it reverts to limp mode. Can then shut off the car and restart, and all the gears work again. Until the next intermittent hard downshift which throws it back into limp mode. The only code thrown upon the limp mode, is a P0700 for generic TCM malfunction.
Would like to know what may be causing the hard downshift and why it then goes into limp mode.
ANSWER: Hi Steve,
There are too many possibilities for that to be specific. It may be an issue simply with the transmission control relay being flakey as when it 'opens' it causes an immediate limp mode. But other things can cause limp mode. So for now, try switching out the trans relay with another relay having the same part number in the powerbox under hood. If that doesn't do it, then a specific code should show up soon.
Roland
PS Please 'rate' my answer, and where you see the question about a nomination of me to be 'volunteer of the month' consider a 'yes' response. Thank you
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QUESTION: Roland
Thank you for the info, it was helpful. I swapped the TCM relay for another relay and that made no difference. I finally got the car in to a Chrysler dealer to read the transmission codes with a DRBIII. This is what it turned up. P1792 battery disconnected, but we knew that. P0731 Gear ratio error in 1st, P1790 Fault immediately after shift, P0715 Input speed sensor, P0720 Output speed sensor. After talking with the tech, although I have replaced the input and output speed sensors with new ones (from NAPA), he said the tolerances of after-markets are not strict enough, and maybe I should try Mopar ones. I've been reading many others comments that after-markets have fixed their problems. So my question is, does it seem reasonable that I should try Mopar sensors before looking at other problems? And, if it is an electrical problem (low voltage or something else), would the DRBIII codes have indicated such. I was glad that it did not return a code indicating a bad TCM module/computer. Thank you for your help.
ANSWER: Hi Steve,
It is good you did another readout and found the 0731. That might be due to an issue with the replacement sensors (I don't have any info about the likelihood of that) or a problem with one of the three wires that connects them to the tcm, or it could be an internal transmission problem that would require a partial or full rebuild. So I would start with the wiring, then the sensors before the last step. At the turbine sensor check the continuity of red/black wire to pin 52 of the tcm, and the dark blue/black to pin 13. At the output sensor check the light green/white to pin 14 of the tcm and the dark blue/black to pin 13. Shake the harness gently while measuring the resistance (continuity) which should be 0 ohms.
Then you might try Mopar sesnors.
If all is the same, then there might be a chance that the solenoid pack or valve body is the issue and those are replaced without removing the transmission but rather dropping a pan and disassembly of the internal parts that way. But the cost may be more than you want to pay on a chance.
Roland
PS Thanks or the rating/nomination/kind remarks.
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QUESTION: Roland,
I'm finally getting back to the Chrysler. I traced the wiring from the input and output sensor harnesses back to the TCM. All four wires test good continuity. I've switched the sensors to the Mopar sensors, although I was doubtful that Mopar would have a much higher tolerance. When I first start the car, I can manually shift 1st, 2nd, 3rd while at a standstill. As soon as I start going, it kicks into limp mode again. It has also thrown the check engine light, codes 1684 (battery) and P0700 again. Same as before.
Does the TCM have a "learning phase" after changing sensors? And if not, does this mean it is probably internal solenoids or pressure switches or something worse? And what is the normal cost if the solenoid pack or valve body needs to be changed out?
Thank you for the guidance.
AnswerHi Steve,
The learn procedure is not needed after a sensor change as far as I know. There are about 28 different trouble codes that are associated with limp-mode so it is difficult to genralize a cause. My thought would be that if you haven't done a readout using a plug in code reader that can access the etax controller that you do that now. The 0700 means there is such a stored code. Then you would have a better idea what is needed to be done. An Autozone or similar nationwide parts store will often do that for free or an independent shop will do it for $40. Get the specific code number and let me know what it is. I don't have experience with the costs of valve body/solenoid pack repairs. In your vehicle the two are mounted together and are accessed by droping the pan underneath the vertical shift rod, to which they are attached.
Roland
